MICROPOWER DIRECT Glossary Of Power Conversion Terms

Alternating Voltage: A voltage that periodically switches direction of flow from positive to negative. — A — The average value of an AC voltage, for a pure sine Absolute Maximum Ratings: Peak perfor- wave, is zero. One cycle (or period) is the time it mance ratings for a power supply. If exceeded, takes the voltage to rise to its maximum value in one permanent damage to a power supply could direction, return to zero, rise to its maximum value in occur. When specified, these specifications are not the opposite direction and again, return to zero. The given as continuous ratings, and proper operation number of cycles per second is the AC frequency. is not implied. Ambient Air: The air mass immediately surround- AC: Abbreviation for alternating current. See Al- ing an operating power supply. Reliable operation ternating Current. of power supplies requires sufficient surrounding air AC/DC: Abbreviation for alternating current/ mass and flow to prevent thermal runaway caused direct current. by heat dissipated by the supply. AC Current: See Alternating Current. Ambient Temperature: The average tem- perature of air immediately surrounding a power AC Front-End: Part of a distributed power system. Temperature measurements should be system that will convert ac line voltage to a made about 0.5 inches from the body of the power semiregulated dc voltage level. An AC front-end supply. See Operating Temperature and Storage will typically provide power factor correction and Temperature. universal (~85 VAC to 265 VAC) ac compatibility. An ac front-end’s output voltage is usually 350 Ambient Temperature Range: The tempera- VDC to 400 VDC. See Power Factor Correction. ture range of air surrounding a power system over which it can be safely operated. Ambient tempera- AC Line: The ac power distribution lines. See ture ranges are often extended by using forced air Alternating Current. flow or power derating requirements. MicroPower Direct AC Line Filter: A filter placed in the ac line to American National Standards Institute: MPD, a leading worldwide provider of pow- condition high frequency noise variations. (ANSI) A US based organization that develops er conversion products, was founded by a AC Voltage: See Alternating Voltage. standards for prod- ucts, processes, and group of industry veterans in 1999. Located Accelerated Stress Testing: (AST) See Highly systems, etc. They in Stoughton, MA, we are committed to de- Accelerated Life Testing and Highly Accelerated also accredit stan- livering innovative, high quality power con- Stress Screening. dards developed by verters at the lowest possible prices. Active Current: The portion of an alternating other organizations. current that is in phase with the voltage. Active We currently off er over 5,000 low cost American Wire Gauge: (AWG) A standard current equals the average power divided by the standard “off -the-shelf” high performance for sizing wire by cross sectional area. AWG has effective voltage. See Average Power, Effective power converters. Our product lines include been used in North America since 1857, it is also Voltage, Reactive Current. DC/DC converters, AC/DC power supplies, known as the Brown & Sharpe wire gauge. The high brightness LED drivers, IGBT drivers Adjustment Range: The range limits over which cross-sectional area of each gauge is an important & controllers, and switching POL regulators. power system parameters may be varied. Typically factor for determining its current-carrying capacity. used with the output voltage of a power supply. Ampere Component selection and layout are care- Often called Trim Range. : (A) The base unit of current, equal to: fully considered at the design stage to op- E Aging: The operation of a power supply under I = timize product reliability. All manufacturing tightly controlled conditions (input voltage, output R is in ISO9000 registered factories under load, ambient temperature, etc.) for a predeter- Where: I = Current strict quality control system guidelines. All mined time. Aging is used in reliability testing to E = Voltage products are supported worldwide, and car- screen out or stabilize marginal units (infant mor- R = Resistance ry a standard three year warranty. tality). See Burn-in. Amplifier: See Error Amplifier. MPD power products have been designed Alternating Current: A periodic current that into a wide variety of products and sys- will symmetrically switch direction of flow from Anode: The “positive” terminal connection to a tems by a very diverse customer base. End positive to negative values. Over a set period of diode, LED etc. See Cathode. time, the average value of an AC current, for a products range from computer peripherals Apparent Power: The product of input rms volt- pure sine wave, is zero. The time period it takes age times input rms current. High rms values in AC to test instrumentation to telecommunica- the current to go from zero to maximum positive tions equipment to process/industrial con- input switch-mode power systems, where the input and back to zero (the positive alternation), then to current is distorted results in high apparent power. trols to medical devices and more. maximum negative and return to zero (the negative alternation) is one cycle. The number of cycles per Applied Voltage: The voltage presented to a second is the AC frequency. circuit point or system input, as opposed to the voltage drop resulting from current flow through applications. Low (or narrow) beam angle LEDs an element. are typically used in indicator applications Assembly: The complete power system, power where a higher luminous intensity is required supply or power converter that is fabricated from (for improved visibility). Also called View Angle, subassemblies and/or various components. Viewing Angle or Beam Spread. Beam Lumens Asymptotic Breakdown Voltage: A voltage : The total lumens contained level, that if applied over a long period of time, within a light beam. will break down insulation. Beam Spread: See Beam Angle. Attenuation: Attenuation typically refers to the Benchmark: A performance standard. Used in loss of power over a length of cable (or board Figure 1 Simplifi ed Balun Filter product, system or component testing. trace), when used regarding power systems. is operating, it reduces the voltage and regulates the Bench Power Supply: A cased power supply Automatic Test Equipment: (ATE) Equipment current to the circuit. This protects the lamp from with displays and controls that are used to precisely (typically a combination of hardware & software) burning out, and the resultant regulated current adjust operating characteristics. Usually an ac used to test/stress power conversion products output produces a steady light output input device, bench supplies are sometimes called or systems. Balun Filter: An input line filter that include a Laboratory Supplies. Autoranging Input: An ac power supply input differential wound transformer often used within Binning: LEDs are sorted as part of the manufac- circuit that senses the input voltage level and au- power supplies. They show high impedance to turing process. Binning helps minimize operating tomatically switches the input to the appropriate common mode signals and low impedance to tolerances in customer shipments. Sort criteria range (i.e. 90 VAC to 130 VAC or 180 VAC to 264 differential mode signals. Also called a Common might include intensity, color, forward voltage, etc. Mode Filter. VAC). Sometimes called an Auto Select Input. Bipolar Junction Transistor:: (BJT) A three Auxiliary Output: A secondary output that is Barrier Strip: A connector that includes a pro- layer, three terminal component whose construc- used to supply low power levels to housekeeping tective barrier between adjacent terminals. Often tion consists of two PN junctions. The two basic circuits etc. It operates separately from the main used on moderate/ high power AC power supplies types are PNP or NPN (which refers to the arrange- output of the supply. or on applications where a wiring harness is used. ment of the N & P type material used). The bipolar transistor acts as a current controlled switch. Average Current:: (IAVG) The average value Baseplate: A metal plate or substrate to which of current flowing in an ac circuit. For a perfect circuit components are mounted or the power Birmingham Wire Gauge: (BWG) A standard sine wave, the value would be zero. The value of supply is attached. It is used to draw heat away used for sizing wire. BWG diameters are larger average current is equal to 0.637 times the value from critical circuit components and (sometimes) than corresponding AWG diameters (for a given of peak current. to provide mechanical stability. See Heat Sink. wire size). Sometimes called the Stubs Gauge.

AVG Pk Baseplate Temperature: See Case Tem- I = 0.637 I Bleeder: See Bleeder Resistor. perature. Average Power: (PAVG) In an ac circuit, the Bleeder Resistor: A resistor that provides a average value of ac power. For resistive circuits, Basic Insulation: The level of insulation required path for current drain. Often used in filter circuits it equals the square of the rms current times the for the proper operation of a power system or to provide a discharge path for capacitors. In circuit resistance, as given by: component and for a minimum level of protection high-voltage power supplies, they can serve as a against electrical shock. It is sometimes called safety circuit. Also called a Drain Resister. PAVG = (Irms)2R Functional Insulation. See also Insulation, Bleeder Power: The power dissipated (as heat) Where: Irms = rms value of the circuit current Double Insulation, Reinforced Insulation and across a bleeder resistor. R = Circuit resistance in ohms Supplementary Insulation. Block Diagram: A simplified diagram of an elec- Average Rectified Current: The average Battery: A multi-cell device that produces DC elec- tronic circuit or system. The different components or value of current from a full-wave rectifier circuit prior tricity via an electrochemical action. Battery cells are parts of the circuit are shown as interconnected box- to any filtering. For a circuit with a sine wave input connected in parallel (to produce a required current) es; making it easier to see the overall system design. and a resistive load, Ir is equal to: and/or series (to produce a required voltage). Blocking Capacitor: A capacitor that will stop Ir = 0.637 IMAX Battery Backup: An electronic equipment sub- the flow of DC current while passing AC current. Average Rectified Voltage: The average system that provides temporary power in case input Blocking Choke: value of voltage from a full-wave rectifier circuit prior power to the system is lost. Battery backed systems : A choke coil or inductor that will to any filtering. For a circuit with a sine wave input range from short term options for AC/DC power stop the flow of AC current while passing DC current. and a resistive load, Er is equal to: supplies to high VA Uninterruptible Power Systems. Board: See Printed Circuit Board. See Uninterruptible Power Supplies (UPS). Er = 0.637 EMAX Board Mount Power Supply: A power sup- Battery Charger : A power supply or power ply or converter that’s designed to mount onto a Average Voltage: The average value of an AC supply output that is used to charge a storage voltage is equal to 0.637 times the maximum value. printed circuit board. Typically refers to product that battery or battery system. is fabricated in an encapsulated module, but low AVG P E = 0.637 E Bead: A small ring of ferromagnetic material. When power open board construction power products slipped over the power leads to a circuit, the bead are available that mount directly to a PC board. — B — acts as a passive electronic choke to suppress high Bobbin: A spool (typically nonmetallic) used in the frequency noise. winding of transformers and inductors. Bobbins Back Ripple Current: See Reflected Ripple Beam Angle: The angle between two lines, on provide a physical frame to support the transformer Current. either side of the optical axis, at a point where or inductor windings and keep the windings isolat- Backup: See Battery Backup. the luminous intensity is 50% of the center beam ed from the core. Backup Battery: See Battery Backup. intensity. It typically ranges from 8° to 160°. High Bode Plot: For a control loop, a plot that shows (or wide) beam angle LEDs (>70°), with their the relationship of gain and phase vs frequency. Bakelite: A plastic resin used as a case material broader spread of light, are useful in illumination for power conversion modules. Part of The loop stability of a power supply is verified the family phenol-formaldehyde plastics. using a bode plot. Boost Regulator Balance Resistors: Resistors con- : A basic switching con- nected in series with LED strings to help verter topology wherein energy is stored in an balance the current in parallel connec- input inductor. When the shunt switch is turned tions. Typically very small values, they off, this energy is transferred to the output. are sometimes called Ballast Resistors. Boost regulators take an unregulated input voltage, and produce a higher, regulated output Ballast: In a fluorescent lighting system, voltage. Also called a Boost Converter. See the ballast regulates current to the lamp. Buck Regulator, Bridge Converter, Flyback At startup, it supplies a voltage high Converter, Forward Converter, Push-Pull enough to start the lamp. Once the lamp Converter and Resonant Converter. Figure 2 Simplifi ed Boost Regulator Page 2 Glossary of Power Conversion Terms Braided Wire: A length of braid typically used for grounding or shielding. Breakdown Voltage: The maximum ac or dc voltage that can be applied from the input to output (or chassis) of a power supply without causing damage. Brick: A packaging standard for DC/DC convert- ers. See Full Brick, Half Brick, Quarter Brick, Eight Brick and Sixteenth Brick. Bridge Converter: A switching converter topology with a full bridge circuit (four switching elements) or half bridge circuit (two switching ele- ments). This topology is more common in off-line (ac input) supplies than DC/DC converters. Bridge converters can provide high output power and low output ripple, but tend to be more complex than other power converter topologies. The added circuit complexity increases cost and may reduce reliability. See Boost Regulator, Buck Regulator, Flyback Converter, Forward Converter, Push- Pull Converter and Resonant Converter. Figure 3 Simplifi ed Bridge Converter British Approvals Board for Telecommunications: Buck-Derived Converter: See Forward Canadian Standards Association: (CSA) (BABT) as established in Converter. Established in 1919, the CSA is 1982 by the British gov- Buffer Capacitor: A capacitor placed across an independent organization that ernment. Now operating sets safety standards (and tests as an independent sub- the secondary of a transformer to suppress volt- age spikes. for compliance) for electronic sidiary of TUV SUD Prod- components and systems that ucts Service, they are a Bulb: Typically used in reference to a lamp. An are to be sold in Canada. See notified body for testing and accrediting a number “LED bulb” is a finished lamp assembly that con- IEC, UL, TUV and VDE. of European telecomm and EMC directives. tains LEDs. Candela: (cd) The luminous intensity of a light British Standards Institution: (BSI) The UK Bulk Capacitor: A storage capacitor often used source in a given direction. At a wavelength of 555 national standards body. They develop standards on the input of a distributed power system. nanometers (green), one candela will have a radiant for a wide variety of organi- intensity of 1/683 watt per steradian. zation requirements includ- Burn-In: To stabilize power supply operation ing health & safety, quality and eliminate infant mortality, newly manufactured Candle Power: See Candela. power supplies are often operated for a period of management, IT security Capacitance: An electrical property that opposes and energy management. time as part of the production process. This “aging” of the unit is tightly controlled, including the time a change in voltage level and stores energy in an They also provide training electrostatic field. and certification to their standards world wide. period, temperature and any special conditions (input power cycling, load switching, etc.). Capacitive Coupling: The coupling of a signal Brownout: A reduction or sag in the ac line or Bus: The primary conductor path (wires, cables, between two circuits or components caused by system power bus. If not protected against sags discrete or parasitic capacitance. (by an adequate hold-up time or extended input etc.) used for routing power to various components ranges), an ac input power system could inadver- within a (sub)system. Capacitive Input Filter: A filter that uses a tently shutdown. Bus Converter: A DC/DC converter that pro- capacitor as its input component. See Input Line vides the isolated intermediate bus voltage in a Filter, Choke Input Filter, Common Mode Filter, Brownout Rated: An ac input power supply Pi Filter and Output Filter. that is designed to operate within specified limits distributed power system. The intermediate bus if a brownout (sag) in the input ac mains or system is used to power non-isolated point of load (POL) Capacitive Load: The maximum amount of ca- power bus occurs. converters. Typically it will be a “brick” type package pacitance in the output load circuit that the power with a 48 VDC input and a 5 to 12 VDC output. supply will drive and is still guaranteed to start and Brute Force Supply: Basic power supply that function correctly. Typically specified as maximum provides an unfiltered/unregulated output. Bypass Capacitor: A capacitor used in ac circuits to provide a low impedance path around capacitive load. If the capacitive load is too high, the Buck Regulator: A basic switching converter a circuit or component. power supply could fail on start up and shut down. topology (see Fig 4) with a series switch (Q1) to chop Capacitor: A passive electronic component the input voltage. The resulting pulses are applied that consists of two metal plates separated by a to an averaging LC filter (L1,C1). Buck regulators will — C — dielectric (insulator). A capacitor stores energy as only produce an output voltage lower than the input Cabinet: See Enclosure. an electrostatic field between its plates. The con- voltage level. See Boost Regulator, Bridge Con- ducting plates are typically made from aluminum, Cable: A bundle of insulated wires through which verter, Flyback Converter, Forward Converter, tantalum or silver. The nonconducting dielectric electrical signals and /or power are transferred. Push-Pull Converter and Resonant Converter. increases a capacitor’s charge capacity. Common Buck-Boost Converter: See Flyback Con- Cable Assembly: A set of wires or cables that dielectric materials include glass, ceramic, plastic verter. connect a power system to the power source or film, air, paper, mica, etc. Capacitors are widely output load. The wires are sleeved; or tied together used in power supplies and other electrical circuits. with cable ties, straps, or Capacitor Leakage: A direct current (DC) that lacing. Also called a Cable flows through the dielectric of a capacitor, leak- Harness, Wire Harness, or age is equivalent to a resistor in parallel with the Wiring Assembly. capacitor. Depending on the capacitance and the Cage: A completely shielded applied voltage, an electrolytic capacitor could have box or room. Typically it is several milliamperes of leakage. A non-electrolytic covered on all sides with a capacitor will typically have less than 1µA. fine mesh screen that is con- Case: See Enclosure. ductive and well grounded. Often used to test systems Case Temperature: The temperature of the or equipment that is sensitive component or power supply case, when the supply to electromagnetic radiation and surrounding system are operating normally. in the surrounding area. Also Often used as a specification (as opposed to ambi- Figure 4 Simplifi ed Buck Regulator called a Faraday Cage. ent temperature) for power supplies with extended MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM temperature ranges or high power densities. It is Figure 5 Central Power System Common Mode Noise: The noise compo- sometimes called Baseplate Temperature. nent that is equal and in phase on conductors with respect to a common reference point. Catch Diode: See Free Wheel Diode. Common Mode Output: Electrical energy Cathode: The “negative” terminal connection to a that is unintentionally supplied to an external device or component (such as an LED). See Anode. impedance that exists between the output con- Ceiling: The maximum amount of current or nection of a floating power supply and a system voltage that power supply or circuit can deliver. common point (chassis, frame, shield, etc.) Cell: The basic unit used in the generation and Compliance Range: The range of voltage storage of electricity. A battery consists of a number required to maintain a given constant current of connected cells. output for a specified range of load resistance. Celsius Scale: A temperature scale based Compliance Voltage: The max dc output on the freezing point of water (defined as 0°C) voltage of a constant current power supply. and the boiling point of water (defined as 100°c). Component: The individual parts (resis- Sometimes called the Centigrade Scale. See also tors, capacitors, etc) used to assemble an Kelvin Scale and Fahrenheit Scale. electronic circuit. Center Tap: A connection made to the center Component Density: The quantity of elec- point of a coil or transformer winding. Used in sim- tronic components on an assembled printed ple power supply designs to develop dual outputs. circuit board per square area. Centigrade Scale: See Celsius Scale. Component Failure Rate: The number Central Power System: A power system in of components, out of a set group, that are which all the components are contained in one expected to fail over a specified period of time. box (or on one card). Often, a central power Typically given as a percentage, however, in system consists of a medium or high power some applications it may be expressed as switching power supply that takes an ac input and the frequency that a component would be generates multiple, regulated dc outputs. These expected to fail. dc outputs are bused throughout the system (via Circulating Current: See Ground Loop. Component Layout: The physical arrangement a wiring harness or backplane) to provide power of components on a printed circuit board. to various system components. Clamp Diode: A diode found in clipper or clamp circuits. The diode will set the voltage level to a Component Stress: The strain that a circuit Certified Europe: (CE) A mark applied to reference point. They are often used as part of a component is subjected to. Typically the higher electronic products (including power supply protection circuit. the mechanical, electrical or environmental stress some power supplies) to be is for a component, the higher the failure rate for sold in Europe. The mark cer- Clearance Distance: The shortest distance that component will be. tifies the power supplies meet (through air) separating two live conductors or the applicable EMI/RFI and/or circuit components. See Creepage Distance. Conductance: The ability of a circuit or circuit safety directives. Clock: Timing pulses used in electronic systems element to conduct electricity. Conductance, mea- sured in mhos (English) or siemens (metric), is the Characteristic: A quantity that defines an operat- to synchronize circuit operation. In a power supply, reciprocal of resistivity and is given by the formula: ing parameter of a device, component or circuit. For clock pulses synchronize operation of the pulse example the output power of a DC/DC given in watts. width modulator (PWM). 1 G = Characteristic Curve: A curve or plot that illus- Color Temperature: A measurement that indi- R trates the relationship between two or more variables cates the hue of a specific type of light source. Warm color temperatures tend to enhance red/orange, Where: G = Conductance with respect to a parameter for a device, component R = Resistance or circuit. For example, a derating curve for a power adding a yellow tint to white. They are typically used supply that graphs the relationship between output in homes, restaurants, etc. Cool color temperatures Conducted Heat: Heat transferred through a power and operating ambient temperature. enhance blue, adding a bluish tint to white. They are material or substance. In power circuits, heat sinks often used in offices, hospitals, etc. Given in Kelvins. are often used to conduct heat away from critical Charger: A circuit or device that charges a ca- components to the surrounding ambient air. pacitor or battery. Comite International Special des Pertur- bations Radio-electriques: (C.I.S.P.R.)The Conduction Cooling: The transfer of heat Charging Current: The current flowing into a International Special Committee on Radioelectronic through a solid material. It is used to cool electrical capacitor when a DC voltage is applied. The current Interference is an IEC committee that develops components or sub-assemblies (such as a power decreases exponentially over time. standards for EMC (CISPR 22). Requirements supply) by the addition of heat sinking. This will Charging Rate: The rate at which current flows are similar to those of the FCC, with significant increase the case surface area of the component into a capacitor or storage cell. changes in frequency limits and the specification of or subassembly, lowering the thermal resistance. “average” limits for testing. See Electromagnetic Thermal resistance equals: Chassis: See Enclosure. Compatibility, Electromagnetic Interference, L Chassis Ground: The voltage potential present Federal Communications Commission and θ = on the chassis, frame or enclosure surrounding a International Electrotechnical Commission. KA power supply. Comite pour Europeen de Normalisation Where: θ = Thermal Resistance Charge Rate: The rate at which current is applied Electronic: (CEN/CENELEC) The European L = Length of material to a battery cell to restore its capacity. Typically Committee for Electrotechnical Standardization) is a K = Thermal conductivity of material expressed as ampere-hours or milliampere-hours. technical committee that recommends standards to A = Cross sectional area of material be adopted by the European Community (EC). Choke: See Inductor. Standards cover EMI/RFI interference, intrinsic Choke Input Filter: A filter that has an inductor product safety, immunity, etc. as its input component. Often used with a capacitor Commercial Grade: (C-Grade) A power (as an L/C filter), choke input filters improve line supply rating for products that do not oper- regulation and are more resistant to input varia- ate below -25°C. See Industrial Grade and tions than capacitor filters. See Input Line Filter, Military Grade. Capacitive Input Filter, Common Mode Filter, Pi Filter and Output Filter. Common: A conductive path used as a return for two or more circuits. When connected to Chopper: See Inverter. earth, a common is the same as ground. See Circuit Breaker: A fuse like protection device Ground. that opens when a circuit is overloaded. Once Common Mode Filter: See Balun Filter. tripped, circuit breakers can be reset. Figure 6 Conduction Cooling

Page 4 Glossary of Power Conversion Terms See Cooling, Convection Cooling, Free Con- Figure 7 Output Current Limiting Current Sensing Resistor: A resistor that is vection and Forced Air Cooling. placed in series with the output load of a power supply. The voltage drop is used to measure load Conductor: A material that allows the easy current. flow of electricity, such as metals, electrolytes, etc. See Insulator. Current Share: To increase system reliability or power, multiple power supplies are often used Conformal Coating: A thin, insulating, coating in parallel. When connected this way, the power applied to a finished printed circuit board assem- supply outputs are strapped together and each bly. It provides protection against environmental unit supplies approximately equal “shares” of the contaminants (dust, etc,). load current. Current sharing can be controlled Constant Current Load: An electronic load passively, by synchronizing multiple converters that maintains a constant current drain on a and trimming the outputs to within a tight margin; power supply. or actively with internal circuits to monitor and Constant Current Power Supply: A power adjust output current. The most popular redundant supply designed to regulate output current to topology is the “N+1” circuit. See Master/Slave, within a specified range for changes in output N+1 and Dual Redundant. load, input line and ambient temperature. Also called a constant current source. Crest Factor: For an ac waveform, the ratio of — D — Constant Voltage Power Supply: A power peak value to RMS value. If the waveform is pure DC/AC Converter: See Inverter. supply designed to regulate output voltage to within sinusoidal, this value is 2. Crest factor was used a specified range for changes in output load, input to approximate the current stress in an AC mains DC/DC Converter: See Converter (DC/DC). line and ambient temperature. circuit. Today, the use of power factor is more DC OK Signal: See Power Good Signal. common. See Power Factor. Continuous Shield: A packaging technique Dead Circuit: A circuit that is electrically disabled. in which the power supply is placed into a metal Crest Value: The maximum value of a waveform Debugging: A process used to identify and elim- case. The metal shielding minimizes noise radia- (excluding transients). inate the fl aws in a circuit, process or machine . tion from the switching components of the power Coupling: See Capacitive Coupling. supply. A continuous shielded case has the base Debugging Period: The period of time following (or header) welded on, further reducing potential Cross Coupling: Unwanted coupling between the completion of a design during which problems noise leakage. Also called Six-Sided Shielding. two circuits. and errors are identified and corrected. Control Circuit: Circuit that controls certain Cross Regulation: In a multiple output power Decay Time: The time required for a pulse to operating parameters of the power supply. Used supply, the change in voltage level on one output, decrease from 90% to 10% of its maximum am- to maintain output regulation. caused by a load change on another output, ex- plitude (either positive or negative). pressed as a percentage. Control Loop: A feedback loop used to control Decibel: A decibel (dB) is the fundamental mea- a power supply output. Crowbar: A protection circuit that rapidly shuts surement unit used in EMI measurements. Given down a power supply’s output when a preset by the equation: Convection Cooling: The transfer of heat via a voltage level is exceeded. A crowbar circuit places fluid motion (typically air). In power subsystems this P0 a low resistance shunt across the output when an 1 dB = 10log10 is normally accomplished by the forced movement over voltage condition exists. PI of air over the power supply case and/or heat sink Where: PO = Output Power surface area. See Cooling, Conduction Cooling, CFM: Cubic Feet per Minute is a common mea- Free Convection and Forced Air Cooling. sure of the volume of air flowing in a system. The PI = Input Power conversion of cubic feet per minute to linear feet Converter (AC/DC): A device that accepts an ac Decoupling: To reduce system noise, it is often per minute is dependent upon the cross-sectional recommended that filter components (typically mF line input voltage and produces a dc output(s). Often area through which the air flows: referred to as a “switcher” (although linear converters capacitors) be connected between the power ter- are available), switching regulated supplies are used CFM = LFM x Area minals of the load in a power system. See Figure 8. in the majority of applications. AC/DC supplies are See Linear Feet per Minute. Decoupling Capacitor: A capacitor that helps available in a variety of form factors, power levels prevent stray coupling between circuits in a system. and feature/performance envelopes. Cuk Converter: A “buck-boost” converter varia- Decoupling capacitors provide a low impedance tion that produces very low output ripple. Typically path to ground. Converter (DC/DC): A device that accepts a used in applications that do not require isolation. regulated or unregulated DC input voltage and See Flyback Converter. Deep Discharge: A cell or battery discharge that produces a DCc output that is that is the same is nearly complete. Sometimes a deep discharge or possibly at a different voltage level. They are Current Foldback: An overload protection is done just prior to recharging. used to provide load isolation, noise isolation local circuit that reduces the output current as the load Density: See Power Density. regulation, etc. approaches short circuit. This minimizes internal power dissipation under short circuit conditions. Derate: See Derating. Cooling: The transfer of heat dissipated by an Also called Foldback Current Limiting. operating power supply into the surrounding Derating: The reduction in output power, voltage ambient air mass. See Convection Cooling and Current Limiting: An overload protection circuit or current required to operate a power supply in an Conduction Cooling. that limits the maximum power supply output cur- environment beyond that typically specified. Nor- rent to a predetermined, safe value. See Current mally used to characterize power supply operation Core: The material that a transformer or an induc- Limit Knee. tor is wound on. In many cases, the core consists of a type of magnetic material (iron, etc.) and provides Current Limit Knee: a path for magnetic flux. The point at which current begins to foldback or limit Core Loss: Power dissipated within the core of a on a plot of output voltage transformer/inductor due to eddy currents or hystere- vs current. See Current sis. Adversely affects the efficiency of a power supply. Limiting, and Current COS: For undistorted sinusoidal waveforms, COS is Foldback. the shift in load current as compared to the ac mains Current Mode Control: voltage. Equal to the difference between apparent A control method used power and true power (for an undistorted sinusoidal with switching converter waveform). See Apparent Power, and True Power. topologies. A dual loop Creepage Distance: The shortest distance control circuit adjusts between two conductors (typically, one primary, the PWM operation in one secondary) measured along the surface of the response to a measured insulation. See Clearance Distance. output current. Figure 8 Power System Decoupling MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM at extended temperatures. See Cooling, Convec- tion Cooling, Conduction Cooling, Forced Air Cooling and Free Convection. Derating Curve: The curve or graph that illus- trates the amount of derating required to operate a power supply in an abnormal environment. Design Validation Test: (DVT) See Design Verification Test. Design Verification Test: (DVT) A test pro- gram designed to ensure that the initial product design goals are achieved. Testing is done at various points in the development cycle and would include product functionality, reliability, EMC/EMI performance, mechanical conformance and en- vironmental tests. Designed To Meet: A term used when a circuit or product has been designed to fit the require- ments of a safety or performance specification but has not actually been certified by an authorized testing facility. Destructive Test: A test that destroys the unit under evaluation as part of the process. See Figure 9 Distributed Power System Nondestructive Test. Distributed Power: A system level architecture oring diodes reverse bias and power supply #2 Deutsches Institut fur Normung: (DIN) The in which a central supply or battery system powers starts to provide full load current. Dual redundant German Institute for Standard- an intermediate power bus (i.e. 24 or 48 VDC). The systems are expensive and not as flexible as other ization, it is the German nation- intermediate bus, routed throughout the system redundant approaches, but they do allow separate al association for developing (normally via a backplane), provides the input input power sources to be used. Sometimes re- standards. They currently have power to a number of DC/DC converters. These ferred to as a “100% Redundant” System. See upwards of thirty thousand converters in turn provide localized power (and Master/Slave and N+1. standards covering a wide various voltage levels) to individual sub-assemblies Duty Cycle: For power supplies, the ratio of “on” variety of technologies and components. The type of power distribution time to “off” time of the semiconductor switch (in system used depends upon the requirements of pulse width modulated “PWM” systems) or clock Dielectric: A material that prevents two points a particular application. in an electrical circuit from becoming conductively signal. In LED lighting systems a PWM input is connected. At times referred to as a Dielectric Distributed-power Open Systems Alliance: often provided as a dimming control. The user Barrier. See Conductor. (DOSA) Formed in 2004, DOSA is a global controls the brightness of the LED by varying the association working to insure compatibility and duty cycle of a PWM wave. Dielectric Breakdown: The sudden, destruc- standardization in the DC/DC board mounted Dynamic Load: An output load that changes tive, conduction of current through a dielectric power conversion market. They have developed rapidly. Normally specified as a load change value that occurs when the applied voltage exceeds the standards regarding form factors, footprints, pin- as well as a rate of change. breakdown value. See Dielectric Withstand and outs, feature sets and other parameters. Breakdown Voltage. Dynamic Response: The output overshoot that

Dominant Wavelength: (d) The wavelength (or occurs when the output load of a power supply is Dielectric Strength Test: See High Potential color) of an LED as perceived by the human eye. Test. either cycled on/off or abruptly changed. This over- Visible LEDs are typically specified by their dom- shoot gives the high frequency output impedance Dielectric Withstand Voltage: The maximum inant wavelength or color. Sometimes referred to of the power supply. See Output Impedance. voltage an insulating material can withstand before as Hue Wavelength or Hue Sensation. suffering punch through or arcing across. See Double Insulation : An insulation barrier made Break Down Voltage and High Potential Test. up of two layers of different insulating materials — E — Differential Mode Noise: The noise component on a conductor. See Basic Insulation, Reinforced Early-Failure Period: The time period immedi- measured between two circuit points with respect Insulation and Supplementary Insulation. ately following the production of a product, during to a common point (minus common mode noise). Drift: With all operating parameters (load, line, which failures may occur due to production errors, equipment failures and/or process issues. See Differential Voltage etc.) held constant, the gradual (and undesirable) : The difference in voltage Infant Mortality. levels measured between two points. change in the output voltage of a power supply over a specified period of time. Typically specified Earth: See Ground. Dimmer: A circuit that will adjust the brightness as starting after a warm-up period. of a lamp or LED. Earth Leakage Current: See Leakage Current. Driver: See Master. DIN Rail: A metal rail upon which the user can Edge Connector: Part of a printed circuit board mount a wide variety of available components Drop Out Voltage: The minimum input voltage (PCB) that has traces etched out to an edge that (including power supplies). Available in a number level required to operate a power supply to within has been formed to fit into a matching socket. specified operating limits. of standard sizes, they are typically mounted inside Figure 10 Dual Redundant Power System a rack or cabinet. Dual-In-line-Package: DIN Rail Power Supply: A power supply that (DIP) Popular package foot- is physically designed to mount on a standard DIN print for low power DC/DC rail. All connections are then made via a wiring converter modules. harness. Some standard board or chassis mount Dual-Redundant: A fully power supplies offer “kits” that will adapt them for redundant power system use with a DIN rail. topology. The circuit consists Direct Current: A current that flows in one of two complete power sup- direction. See Alternating Current. plies connected in parallel. Power supply #1 runs “hot”, Discrete Circuit: A circuit or subassembly supplying all the load current, comprised of discrete components (resistors, while power supply #2 runs diodes, FETs, etc.) as opposed to an assembly “cool” (disconnected from comprised of integrated components. the load via oring diodes). Dissipation: See Internal Power Dissipation. If the “hot” supply fails, the

Page 6 Glossary of Power Conversion Terms Eddy Current: A circulating current induced by Figure 11 ESL and ESR variations in a magnetic field. Eddy Current Loss: The energy losses in a system/component due to eddy currents. Effective Current: See Effective Value.

Effective Value; (IEFF) The value of an alternating waveform that has an effect on a resistance that is the same as an equivalent value of DC voltage or current. The effective value equals the RMS (Root Mean Square) value. For sine waves this equals:

XEFF = 2 x Peak Value

If the maximum current (IMAX) or voltage (VMAX) of the waveform is known, the effective value can be determined by: popular power conversion topologies) and reflected ronment, provides mechanical stability, insulation and XEFF = 0.707 x IMAX (or VMAX) back onto the input power bus. Improved design helps to draw heat away from internal components Effective Voltage: See Effective Value. techniques (such the use of PFC) have reduced this to the outer case. Also called Potting. issue. Acceptable limits for conducted EMI are set Efficiency (␩): The ratio of total output power to Enclosure: The case/container used to package by various agencies (FCC, IEC, etc). input power expressed as a percentage. Expressed a power supply. Enclosures, which range from as a percentage, efficiency is derived by the equation: Radiated EMI - Noise generated by a power sup- small plastic shells to sophisticated metal cases, ply that is emitted into the area surrounding a power protect internal components from the outside PO system. Radiated EMI, consisting of broadband environment; provide mechanical stability and ␩ (%) = x 100 radio frequencies and narrow band emissions is in some applications improve thermal and noise PI also limited by various agencies (IEC, VDE, etc.). performance. See Open Frame and L-Frame. Where: ␩ = Efficiency Typically, it is controlled by shielding. Energy Loss: See Power Loss. PO = Output Power Electromagnetic Susceptibility: (EMS) PI = Input Power Energy Storage Device: See Capacitor. The tolerance of a power supply, circuit or system Efficiency may vary under differing operating condi- to electromagnetic energy that could cause a Environmental Factors: Characteristics of tions, and is normally specified at full rated output degradation in performance or failure. Sometimes the area immediately surrounding a power supply power, nominal input line conditions and +25°C. called Electromagnetic Vulnerability. or system that might affect performance. These Efficiency has become an increasingly important might include temperature, moisture, electrical Electromechanical power supply specification with the rising demand : Describes a mechanical noise or vibration. for higher power density systems. device or process that is controlled electrically. Epoxy Resin: See Encapsulent. Electronic Breadboard Eighth Brick: A packaging standard for DC/DC : A board or card that Equivalent Series Inductance: (ESL) The converters. Its dimensions are 2.3 x 0.9 inches has prepunched holes that allow the quick assembly inductance in series with an “ideal” capacitor. ESL (57.9 x 22.8 mm). Other established package of electronic circuits. Used to test and evaluate circuits 1 1 1 during the development or improvement of products. sources include terminals, electrodes etc. standards include full, ⁄2, ⁄4, and ⁄16 bricks. Electronic Industries Alliance: (EIA) An Equivalent Series Resistance: (ESR) The Elastance: (F-1) The opposition of a capacitor resistance in series with an “ideal” capacitor. ESR to being charged. It’s the reciprocal of the Farad industry standards and trade association. Started sources include lead resistance, terminal losses, and is expressed by the unit “daraf”. It is typically in 1924, it ceased operations in 2011, splitting etc. It’s an important specification for high frequen- referred to as “reciprocal farad”. into its six divisions. These are the Electronic Components, Assemblies; Equipment & Sup- cy applications. Electrode: A terminal used to conduct electricity plies Association (ECA); the JEDEC Solid State Error Amplifier: An amplifier used in the control or to which electricity is applied. A positive elec- Technology Association (JEDEC once called feedback loop of a power supply. It produces an trode is typically called an Anode and a negative Joint Electron Devices Engineering Councils); error voltage when the sensed output (tapped electrode is typically called a Cathode. the Government Electronics and Information off a voltage divider network) differs from a refer- Electrolysis: The process of passing a direct cur- Technology Association (GEIA); the Telecom- ence voltage. The error voltage adjusts the PWM rent through an electrolyte, producing a chemical munications Industry Association (TIA); and operation to correct the sensed output voltage. change in the solution and the electrodes. the Consumer Electronics Association (CEA). Sometimes called a Reference Amplifier. Electrolyte: A substance that ionizes when Electronic Load: Test equipment which will Eye Sensitivity: A curve depicting the sensitivity dissolved in an ionizing solution. If electrodes are draw precise current or power levels from a power of the human eye as a function of wavelength (color). placed into the electrolyte and a voltage is applied, supply. Often used as part of an ATE setup. See the electrolyte will conduct electricity. Automated Test Equipment. Electrolytic Cell: See Electrolytic Capacitor. Electrostatic Shield: See Faraday Shield. — F — Failure: The state or condition wherein a power Electrolytic Capacitor: A type of capacitor Electrostatic Discharge: (ESD) Current produced by two objects having a static charge converter is not operating correctly or not oper- used in power supplies that consists of two plates ating at all (or electrodes) separated by an electrolyte. when they are brought close enough to produce an arc or discharge. Failure Analysis: The process of determining the Electromagnet: A magnet that uses an electric mode or cause for the failure of a power converter. current to produce a magnetic field. Simply, an Enable: A signal that can turn a power supply on. insulated coil of wire is wound around a core of Often specified as part of a remote ON/Off control Failure Mode: The reason a power supply or ferromagnetic material (such as iron). The strength capability. See Inhibit and Logic Inhibit/Enable. system either does not meet or stops meeting of the feild can be varied by changing the amount Encapsulant: A material into components, or specified parameters. of current in the winding. circuits are embedded. Typically a synthetic epoxy Failure Rate: (λ) As used in reliability engineering, Electromagnetic Compatibility: (EMC) Pow- resin is used for modular power supplies. Often it is the rate at which a system, product or com- er supplies and systems must be designed to operate called Potting Compound. ponent fails, expressed in failures per unit of time. within their intended environment without interfering Encapsulation: The process of embedding a In actual practice, the mean time between failure with other components, and without being adversely circuit or component into an epoxy resin. The epoxy (MTBF) of a product is typically used instead of affected by other components. EMC is divided into is typically applied as a thick liquid which is then failure rate. See Mean Time Between Failure. two main areas: electromagnetic interference (EMI) cured (allowed to solidify) by air or by heating it. Great Fan Cooled: See Forced Air Cooling. and electromagnetic susceptibility (EMS). care must be taken to remove voids, to not to stress Farad: (F) The basic unit of capacitance. When Electromagnetic Interference:(EMI) components (such as windings, glass diodes, etc) a charge of 1V per second across a capacitor Conducted EMI - Noise generated by a power and to insure the epoxy fully cures. Once cured, the produces a current of 1A; that capacitor has a supply (typically by the switching action of the more epoxy protects the circuitry from the surrounding envi- capacitance of 1F.

MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM Faraday Shield: An electrostatic shield that Figure 12 Simplifi ed Flyback Converter reduces coupling capacitance in transformers. The shield, which reduces output common mode noise, is placed between the primary and secondary windings of a transformer. Fatigue: The degradation of a component or circuit over time or under repeated stress. Fault: A device, circuit or component failure. Fault Mode Input Current: The input current (typically a momentary surge) drawn by a power supply when the output is shorted. Fault Tolerant: A power system configuration op- Finned Surface: This refers to “fins” added to a Forced Air Cooling: The use of a fan (or other timized for continuing operation without shutdown. heat sink. The fins increase the surface area of the air moving equipment) within a (sub)system to Typically involves the use of a redundant topology heat sink, thus increasing its effectiveness. move air across heat producing components in (i.e. N+1, etc.) and the ability to remove and replace order to reduce the ambient temperature. See power modules without disturbing system operation Fixed-Frequency: For a power supply, this Convection Cooling, Free Convection and (hot-plug capability). Thus, the failure of any one typically refers to the switching frequency of the Forced Convection. power module will not cause a system failure. unit. For many power supplies, the switching frequency will vary with changes in the load. A Forced Convection: An operating environment Federal Communications Commission: “fixed frequency” supply will operate over a wide in which air movement induced by a fan, blower, (FCC) A US government agency range of load conditions with little or no change. etc. is used to maintain power modules within that sets standards for, and gov- operating limits. See Convection Cooling, Free erns the testing of conducted and Flag Signal: A status or alarm signal generated Convection and Forced Air Cooling. radiated emissions. These are by a power system. Often displayed as a front panel system level standards, but they are LED or provided as output logic signals (normally TTL/ Forward Converter: Like the flyback circuit, a often used in specifying power sup- CMOS compatible). Typical signals would indicate forward converter uses a single transistor switch. plies. See Electromagnetic Interference (EMC). “Power Good”, “Power On”, “Over temperature”, etc. However, in the forward converter, energy is transferred to the transformer secondary while the Feedback: The process of returning part of the Floating Output: A power supply output that transistor switch is “ON”, and stored in an output output signal of a power supply to its input, where is ungrounded and not referenced to another inductor. Also called a Buck-Derived converter. it is used to control or regulate the output. output. Typically, floating outputs are fully isolated and may be referenced positive or negative by the See Boost Regulator, Buck Regulator, Bridge Feed Forward: A method of improving line reg- user. Outputs that are not floating share a common Converter, Flyback Converter, Push Pull Con- ulation by directly sensing the input voltage of the return and as such, are referenced to one another. verter and Resonant Converter. power converter. See Line Regulation. FR-4 Flyback: The voltage spike that occurs across an : A grade designation for laminate sheets Ferrite: A ceramic compound composed of inductive load when the supply voltage is reduced used to produce printed circuit boards. FR-4 is iron oxide combined chemically with one or more suddenly or removed. See Flyback Diode. a fire resistant, composite material consisting of additional metallic elements. Soft ferrite’s used in woven fiberglass cloth with an epoxy resin binder. transformer/electromagnetic cores contain oxides or Flyback Converter: Sometimes called a “buck- See Printed Circuit Board. boost” converter, this topology minimizes the carbonites of metals such as zinc, nickel or manga- Free Convection required components by using a single transistor : An operating environment in nese. They have low losses at high frequencies and which the natural movement of air (unassisted by are used extensively in switching power supplies. switch and eliminating the need for an output in- ductor. During the first half of the switching period, fans or blowers) is sufficient to maintain the power Ferrite Bead: A small ring of ferrite that is when the transistor switch is “ON”, energy is stored module within its’ operating limits. Also called slipped over a wire or cable to reduce or eliminate in the transformer primary. During the second half Natural Convection. See Convection Cooling,

radio-frequency noise. or “flyback” period when the switch is “OFF”, this Forced Air Cooling and Forced Convection. Ferroresonant Transformer: A transformer energy is transferred to the transformer secondary Free Wheel Diode: See Flyback Diode. and load. This technique is cost effective because in which part of the core is driven into saturation Forward Current: (IF) The current that flows of the minimum number of components required. by a resonant tank circuit. The output of the through a semiconductor junction (such as an LED) See Boost Regulator, Buck Regulator, Bridge transformer, taken from the saturated portion, is when it is forward biased. relatively immune to variations in input voltage. Converter, Forward Converter, Push Pull Con- Used in ferroresonant power supplies. verter and Resonant Converter. Forward Voltage: (VF) The voltage drop across a semiconductor junction (such as an LED) when Flyback Diode: A diode connected across the Field Angle: Similar to “Beam Angle”, but given at it is forward biased. a point where the luminous intensity is 10% of the transformer secondary to reduce voltage spikes center beam intensity. See Beam Angle. caused by the switching action of the power Frequency of Operation: See Switching transformer. Sometimes referred to as a Snub- Frequency. Field Effect Transistor: (FET) A transistor that ber Diode, Freewheeling Diode, Suppressor uses a high impedance gate to control the flow of Front End: See AC Front End. Diode, Clamp Diode or Catch Diode. current through a thin “channel” of semiconductor Full Brick Converter: A standard package size material (typically silicon). FETs have four connec- Foldback Current: See Current Limiting and for high power density DC/DC converters. A full tions, gate, source, drain and body. A voltage Current Limit Knee. brick typically measures about 4.6 x 2.4 Inches applied to the gate regulates the conductivity (via an Foot-candle: The illumination on a one square (116.84 x 60.96 mm). There is some variance be- electric field) of the channel. A depletion FET is nor- foot surface set one foot from a one candela light tween manufacturers. Other established package mally OFF and an enhancement FET is normally ON. 1 1 1 1 source. Equal to one lumen per square foot. standards include ⁄2, ⁄4, ⁄8, and ⁄16 bricks. Filter: A circuit that passes one frequency or band of frequencies while blocking others. See Figure 13 Simplifi ed Forward Converter Input Line Filter, Common Mode Filter, Pi Filter and Output Filter. Filter Capacitor: A common component in power supply circuits, filter capacitors are used to pass AC noise to ground. They are typically connected across the input/output of a supply. Filter Inductor: A common component in power supply circuits, inductors are used to block AC noise. They are typically connected in series with the power line being filtered. They are often used with capacitors to form an LC, Pi or T filter.

Page 8 Glossary of Power Conversion Terms Full Bridge Converter: A power supply topolo- Ground Fault: Circuit failure caused gy, typically configured as a forward converter, that by the loss of a ground connection. uses a bridge circuit, consisting of four switching Ground Loop: When two or more transistors, to drive the transformer primary. See system components share a common Bridge Converter. ground line, a feedback (ground) loop Full Load: The maximum value of output load is induced. This can cause unwanted specified for a converter under continuous oper- voltage levels within the system. ating conditions. Ground Noise: Circuit noise caused Full-load Current: The output current from a by a faulty ground connection. source when the load is maximum (that is, the load Ground Plane: A conductive pad resistance is minimum). on the printed circuit board, set at Full Load Power: The power drawn from a ground potential, upon which a power supply when it is operating at maximum rated load. supply is mounted. Shields system Full Load Voltage: The output voltage of a supply components from possible RFI noise when it is operating at maximum load. generated by the supply. Ground Potential Full Wave Rectifier: A circuit (bridged or center : Potential of the Figure 15 Heat Sinks tapped) that rectifies both halves of an ac waveform. ground point in a circuit as referenced to other circuit voltage levels. Heat Rise: The increase in component/subas- Fuse: A circuit protection device, consisting sembly temperature caused by self-heating or Ground Resistance primarily of a low melting point wire. If current : The DC resistance of a heat absorption. connection to ground or earth. passing through the wire exceeds a set level (as Heat Sink: A metal extrusion plate etc used to in the case of a fault condition), the wire melts and Ground Return: The circuit point or path used transfer heat away from sensitive components or the circuit opens. as a return to ground either to compete a circuit, circuits. See Baseplate. Fusible Resistor or for safety. : A resistor used to protect Heat Sink Resistance: The resistance to heat all, or parts of a circuit. The resistor (typically low flow within a heat sink. value) will open up if it’s current rating is exceeded. — H — Heat Sink Temperature: The average tem- 1 Half Brick Converter: ( ⁄2 Brick) A standard perature of a heat sink attached to a power system — G — package size for high power density DC/DC con- component during normal operation. Under typical Gate: A circuit or component that has no output verters. A half brick typically measures about 2.4 operating conditions, heat sink temperature will until it is triggered by a control signal (or level). x 2.3 Inches (61 x 58 mm). There is some variance be lower than the component case (or baseplate) between manufacturers. Other established pack- temperature. 1 1 1 Galvanic Isolation: Two circuits which have age standards include full, ⁄4, ⁄8, and ⁄16 bricks. no significant ohmic connection are “galvanical- Heat Transfer: The movement of heat from one Half-Cycle ly isolated” from each other. Galvanic isolation : One half (180° of phase) of a com- part of a system or circuit to another. The transfer (separation) is achieved by using a transformer, plete AC wave. is typically made by conduction, convection, or opto-coupler, etc. Half Bridge Converter: A power supply topol- radiation. Gauge: An instrument or device used to measure ogy that uses a bridge circuit, consisting of two Henry: (H). The standard unit of inductance. The the magnitude of a circuit parameter. Also used switching transistors, to drive the transformer pri- inductance of a circuit is one Henry when 1V is to describe the standard thickness of wire. See mary. Half bridge converters are typically configured produced by a current that is changing at 1 A/S. Wire Gauge. as a forward converter. See Bridge Converter. Typical values of inductance used in circuitry are Half Wave Rectifier micro henry (µH) and millihenry (mH). Generator: A piece of equipment that produces : A single diode circuit that electricity. rectifies one half of an AC waveform. Hertz: (Hz) The standard unit of frequency. The Hardware: The mechanical & electromechanical Hz is equivalent to cycles per second. One Hertz Go-No-Go Test: A test that indicates only pass is equal to 1 cycle per second. or fail. No other information is provided. components of a circuit or system. Harmonic: (H) A component whose frequency Hiccup Mode: An operating mode in which an Gram: (g) A unit of mass a weight. It is equal to output fault condition (short-circuit) causes the 0.001 kilogram or 0.0353 ounce is an integer frequency of the fundamental sys- tem frequency. For power supplies, harmonics power supply to cycle on and off. The duty cycle Ground: An electrical connection that is made to are caused by nonlinear loads. See Harmonic of the on/off cycle is set to maintain the internal earth (or a conductor that is connected to earth). Distortion. power dissipation at a safe level until the fault A power converter “common” is not actually condition is corrected. Harmonic Distortion: For sinusoidal AC ground unless it is somehow connected to earth. High Line: The maximum input line voltage spec- See Common. current waveforms, the load current distortion caused by the presence of multiple harmonics of ified for normal power supply operation. See also Ground Bus: A grounded conductor or circuit the fundamental frequency (the frequency of the Low Line and Input Voltage Range. trace to which various system components are AC mains voltage). High Potential Test: (Hipot Test) A test that connected. Head Room: For a series pass regulator, refers to determines whether a power supply passes its Ground Connection: A low resistance con- the difference between the input and output voltages. minimum break down voltage specification. See nection to earth. Breakdown Voltage. Heat: A form of energy that is transferred between two bodies having different temperatures. Highly Accelerated Life Testing: (HALT) A Figure 14 Ground Plane The transfer (from a hot body to a cooler process in which a product is stressed by a variety one) is done by conduction, convection, or of environmental factors (temperature cycling, power radiation. The amount of heat transferred is cycling, vibration. etc). Stresses are applied until the expressed in degrees, British thermal units product fails. The product is repaired and the testing (BTU’s), calories, joules, or kelvins continues until the stress levels are significantly beyond what the product is expected to see in actual use. The Heat Aging: See Burn In. HALT process is used to identify design defects before Heat Exchanger: A device or system a product is released. that draws heat from a hot component Highly Accelerated Stress Screening: (HASS) and transfers it to another component or A process in which a product is stressed by a variety of into the surrounding air. See Heat Sink. environmental factors. Unlike HALT testing, the stress- Heat Flux: The fl ow rate of heat across or es are over the specified limits of a product, but within through a material. Given in units of W/cm2. the safe operating limits of the design (product life is not reduced). HASS testing is used to identify potential Heat Loss: Power lost as a result of heat problems with product design and/or production. It is dissipation in a power supply. applied to 100% of production.

MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM Hipot Test: Abbreviation for High Potential Test. Input Power: (Pi) The pow- Hold-up Capacitor: A capacitor on the input of er present at the input to a a distributed power system. The hold-up capaci- circuit or component. tor will maintain or “hold-up” the input voltage to Input Protection: A com- the power system in the event a fault causes a loss ponent or circuit that protects of the input bus voltage. The capacitor has to be the input of the power supply selected to have sufficient capacity to maintain the from damage in the event a input until the fault condition is removed (typically fault occurs on the input bus the time required for a fuse to blow). (surge, transients, short, etc). Hold-Up Time: Following a loss of input power, Protection circuits can range the period of time an AC/DC power supply output from a simple fuse to a full will remain operating to within specification. EMC/protection module. Input Reflected Ripple Hot Line: The line or bus that provides the AC Current current to a circuit. See Ground and Neutral Line. : The AC compo- Figure 16 Isolation nent (typically generated by Hot-Plug: A fault tolerant feature that allows the switching circuit) measured at the input of a International Electrotechnical Commission: power supplies to be inserted or removed from a power supply. Given as a peak to peak or rms value. (I.E.C) An organization based in Switzerland that system while it is powered and operating. Power sets standards for electronic Input Surge Current: See Inrush Current. supplies must be specifically designed for this fea- products and components. IEC ture to avoid causing damage to the power supply Input Transient: A spike in the input line to a does not conduct any testing, or disturbing other modules and sub-assemblies power supply. Input circuits/components are used however, their standards have connected to the system power bus. to absorb or clip transients, shielding sensitive been adopted by many of the na- Hot-Swap: See Hot-Plug. components from possible damage. tional safety/standards agencies. Input Voltage Range Hybrid: See Hybrid Circuit. : The minimum and International Organization for Standards: maximum input voltage limits within which a power (I.S.O.) Established in 1947, the I.S.O. Hybrid Circuit: A circuit in which two or more supply will operate within specifications. For DC/DC is a worldwide federation of stan- dissimilar technologies are used. converters, it is typically given as a percentage or ra- dards bodies that works to promote Hysteresis: The tendency of a magnetic material tio of high line to low line (i.e. a range of 18 VDC to 36 the harmonization of international that is subjected to an alternating magnetic field, to VDC is 2:1 and a range of 9 VDC to 36 VDC is 4:1). standards. Thousands of companies saturate and retain some of its magnetism when For operation in railway systems and PV systems, now comply with ISO 9000 and ISO the field reverses polarity. much wider ranges are available. For AC/DC power 14000 standards. supplies, operation in Europe and North America Inverter: A circuit that converts DC power to Hysteresis Loss: The power loss caused by requires an input range that accepts nominal levels AC power. hysteresis in a magnetic material exposed to an al- of 110 VAC & 220 VAC and it is normally specified ternating magnetic field. The loss ( as heat) depends as “universal” (90 VAC to 264 VAC), auto-ranging or lluminance: A measure of the intensity of light upon the volume & grade of the core, the frequency user selectable. Some supplies now have inputs that on a surface. Measured in foot-candles or lux, it is of the magnetic field and the value of flux density. accept up to 305 VAC for use with a 277 VAC bus. inversely proportional to area. Inrush Current: At turn on, the maximum, Isolated Output: See Floating Output. — I — instantaneous input current drawn by a power Isolating Diode: A diode used to pass a signal IGBT Driver: A hybrid component used to sim- supply. Also called Input Surge Current. or voltage level in one direction, but block them plify the design and control of high power IGBT Inrush Current Limiting: A protection circuit from the other direction. circuits. Typically they include circuitry to control that limits the current a power system draws at Isolation: The electrical separation between the the gate drive; provide safety circuits; isolate power turn on. input and output of a power converter. Normally sources; and optimize circuit timing. Insulated Gate Bipolar Transistor: (IGBT) determined by transformer characteristics and Impedance: The total opposition offered by a The IGBT combines features of the bipolar component spacing, isolation is specified in val- circuit/component to the flow of ac current. transistor (BJT) and the metal oxide field effect ues of VDC for DC/DC converters and VAC for AC power supplies. Isolation resistance (typically Incoming Inspection: The examination and transistor (MOSFET). It has the voltage controlled megohms) and capacitance (typically picofarads) testing of components and materials as they are re- gate drive of the MOSFET and the high current are also common specifications. ceived. In this way, faulty components can be iden- conduction channel of the BJT. This combination tified and separated before reaching production. has made the IGBT the preferred device for high Isolation Voltage: The maximum voltage (ac or dc) that can be continuously applied between In-Circuit Tester: A test system that allows power switching applications. isolated circuits without a breakdown occurring. components to be tested without removing them Insulation: A non-conductive material used For power supplies, it is normally specified as from the circuit in which they are wired. to protect & separate electronic components or input-output or input-case isolation. Minimum circuits. Inductance: An electrical property that opposes isolation voltage levels must be maintained to the flow of current in a circuit when a voltage is Insulation Breakdown: The rupture or breech meet most safety regulations. Typical isolation applied (or a change in an established current). It of an insulating material due to high voltage stress, levels range from 1 kV for low power DC/DC’s to is measured in Henries. that allows the flow of current. 3 kVAC for AC power supplies. See Breakdown Inductive Load: A load that is inductive in nature, Insulation Resistance: The resistance offered Voltage, High Potential Test and Isolation. such as electric motors. by an insulating material to current flow. Inductor: A coil or winding with inductive properties. Insulator: A material that stops the flow of — J — Inhibit Signal: A signal that can shut a power electricity. Joule: (J) The standard unit of work or energy. It is supply off. Often specified as part of a remote ON/ Internal Power Dissipation: The power dis- equal to the work performed by a force of one new- Off control capability. See Logic Inhibit/Enable. sipated as heat within the power supply during ton when its point of application is moved a distance normal operation. Primarily a function of the power of one meter in the direction of the applied force. Input Capacitor: The first capacitor in a capac- itor-input filter. handling capability and efficiency of the power sup- Joule Effect: The heat released by a current ply. Internal power dissipation is normally given as flowing through a resistance. Also called Resistive Input Current : The current drawn from the input a maximum specification that cannot be exceeded Heating or Ohmic Heating. power bus by a power converter when operating without risking damage to the power supply. under nominal conditions. Joule’s Law: The rate at which current flowing International Commission on Illumination: in a constant-resistance circuit produces heat is Input Line Filter: A low-pass or band-reject (CIE) The international standard- proportional to the square of the current. filter on the power supply input (internal or external) ization body on light, lighting, that attenuates noise from the system power bus. illumination, color, and image Jumper: A piece of wire (typically flexible & in- See Common Mode Filter, Filter and Pi Filter. technology. Established in 1913, sulated) used to temporarily connect two points Input/Output Isolation: See Isolation. it based in Vienna, Austria in a circuit. Page 10 Glossary of Power Conversion Terms Junction Diode: A semiconductor diode created switching and linear power supplies, by forming a P-N junction. The diode will conduct this is not significant, but it is an im- in one direction. portant specification in ferroresonant Junction Field Effect Transistor: (JFET) See power supplies. Field Effect Transistor. Line Regulation: The change in output voltage caused by varying the input voltage over a specified range — K — (with output load, temperature, etc Kelvin: (K) The standard unit of thermodynamic remaining constant), expressed as a temperature. The kelvin is based upon an absolute percentage. thermodynamic temperature scale with a null point Line Transient: See Input Transient. of absolute zero. It’s defined as 1/273.16 of the thermodynamic temperature of the triple point of Line Voltage: The ac input voltage water (0.01 °C or 32.018 °F) to a power system, taken off the mains. Figure 17 L-Frame Construction Kirchhoff’s First Law: In a DC circuit, the sum Linear Feet per Minute: (LFM) A measure of of the currents flowing out of a point will equal the Life Test: A power supply reliability test in which the velocity of air. Often used in power systems sum of the currents flowing into that point. units are operated (typically under accelerated to give the air flow over a baseplate or heatsink conditions) over some period of time in order to surface area required to meet specified operation. Kirchhoff’s Second Law: In a DC circuit, the al- approximate life expectancy. LFM is equal to: gebraic sum of all the voltage drops around the circuit (including supply voltages) is always equal to zero. Light Load: A power supply load that is a small m/s multiplied by 196.8 fraction of its normal level. Where: m/s = meters per second Limit: The lowest or highest level of a power supply — L — specification. Often refers to specification levels that Linear Power Supply: A power supply that L-C Filter: A low pass filter consisting of a series could potentially damage a power supply if exceeded. uses linear regulation. Linear’s provide excellent regulation, low output noise and fast transient re- inductor followed by a shunt capacitor. Often used Line: Bus used to deliver power to the input as an input filter in low power converters. sponse. However, they are typically much heavier, (terminals, pins, etc.) of a power supply. See Bus, larger and less efficient then “switchers”, which are L-Frame: A type of power supply construction High Line, Mains and Low Line. now much more popular. See Switchers. in which the assembled power unit is mounted Line Cord: A two or three wire insulated Linear Regulation onto an “L” shaped metal frame (see Figure 18). : A regulation technique in conductor used to connect equipment to the which the regulating device (typically a transistor) This frame is used as heat sinking for critical power line. components and gives mechanical stability to the is placed in series or parallel with the load. Voltage entire power supply assembly. In the application, Line Current: The ac input current to a power variations across the load are then controlled by the L-frame is typically attached directly to the system, taken off the mains. changing the effective resistance of the regulating users equipment chassis. See Open Frame and device to dissipate unused power. See Series Line Drop: The voltage drop across a line sup- Regulator, Shunt Regulator and Post Regulation. Enclosure. plying power to a component or system. Linear Regulator: A voltage regulator that Lagging Load: An inductive load (current lags Line Effect: See Line Regulation. voltage). utilizes a transistor or other device (zenor diode, Line Frequency Regulation: The change in etc) to control the output voltage. This method is Lamp: A device that converts electrical energy output voltage caused by a variation in input line inherently inefficient, as the regulating component is into visible light. Many different types of lamps are frequency, all other factors remaining constant. In dropping the difference between the input voltage available including, incandescent, fluorescent and and the regulated output voltage. For low power neon. Increasing lamps consisting of LED arrays applications, this power loss may not be signifi- are being used. See LED. cant, and in these cases linear regulators can be Lead Frame: A metal frame that holds the pins a cost effective solution. See Linear Regulation, or components of a power supply in place during Switching Regulation, Switching Regulator. encapsulation (after which it is cut away). Very Line Filter: A circuit that is put on the input lines to common in the manufacture of semiconductors, a power supply to suppress noise and interference. lead frames are now used on low power DC/DC Line filters can range from simple Pi or LC filters to converters. Also called a Pin Frame. more complex circuits that meet EMC/EMI standards. Leading Load: A capacitive load (current leads Line Noise: Random fluctuations (noise) on the voltage). input line to a power supply. See Line Filter. Leakage Current: At a set voltage level, the Live: A wire, circuit trace, etc that is connected to current flowing from input to output or input to a power source and has a potential that is different case of an isolated power supply. For an ac input than earth ground. power supply, the current that flows from the Load primary circuit to earth ground. Excessive leakage : The electronic components or circuitry pow- current may pose a hazard to system operators if ered by a power system. The load characteristics the earth ground is disconnected. For this reason, (resistance, reactance, etc) determine the amount safety agencies regulate allowable levels of leakage of power drawn from the power supply. current. Load Capacitance: The capacitance present LED: (Light Emitting Diode) A diode that emits in the output load of a power supply. Most power photons (as light) when forward biased. supplies are tested & specified for the maximum capacitive load that they can drive. Adding too LED Driver: A power supply with a constant much capacitance to the load circuit of a power current output. LED’s are current controlled semi- supply could cause start up issues. At start up, load conductors and most power supplies have voltage capacitors draw high current levels as they charge. controlled outputs. There are an increasing number If it this current level is too high or if it takes too long of constant current power sources available spe- to charge, the over current protection (built into most cifically designed to power LED arrays. power supplies) could trip; shutting the unit down. LED Strip: LEDs that are attached to a flexible PC Load Decoupling: See Decoupling. board up to about 16 feet long and put on reels. Load Effect The user can then trim the strip to the size required. : See Load Regulation. Load Regulation Life: The time period over which electronic : The change in output voltage components, equipment or systems will operate caused by varying the output load over a specified before they fail. range (with input line, temperature, etc. remaining Figure 18 Typical LED Bulbs constant). It is expressed as a percentage. MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM Luminous Intensity: The per- with PWM (Pulse Width Modulation) controlled ceived power emitted by a light power supplies. source in a single direction. It is Minimum Operating Temperature: The min- the luminous flux per unit solid imum temp. at which a power supply will operate angle steradian (sr). Expressed in within specified operating parameters. Normally candelas (cd). specified as either ambient or case. Lux : (lx) The measure of light in- Modification: Changing the configuration, pack- tensity, as perceived by the human aging or specifications of a power supply to meet eye. One lux equals one lumen per square meter. a specific customer demand. Modular: Term used to describe the physical — M — construction of power systems that consists of Magnetic Core: See Core. separate sub-assemblies. Modular construction tends to lower the design turnaround for custom Mains: See Ac Line. products, but increases cost and lowers MTBF. Magnetic Shielding: Enclosing a power Modulator: See Pulse Width Modulator. transformer with conductive material to reduce interference caused by the magnetic field. Module: An encapsulated or potted power supply. Margining: A system performance test, in which Mold: The container used in the injection molding the power supply output is adjusted up and down process. Power supply circuits are placed in the (typically by 5%). It is used to verify the resilience mold (typically on a pin frame). Then liquefied epoxy of a system to power supply voltage fluctuations. is forced into the mold under pressure. After the epoxy cools and solidifies, the individual modules Master: In a master/slave system, the intelligent are separated. Figure 19 Simplifi ed Master Slave Connection power supply. The master supply contains the feed- back loop for the power subsystem, and thus con- Molded: A component or subsystem that is Load Sharing: See Current Sharing. trols output regulation. Sometimes called a Driver. completely enclosed in an insulating material (such Local Sensing: Using the output terminals of as plastic). Some low power converters are now Master/Slave Operation: The connection of available as molded units. the power supply to provide feedback to voltage two or more power supplies in which one (mas- regulation circuits. See Remote Sensing. ter) controls the operation of the others (slaves). Mylar: A plastic material (polyethylene terepha- Logic Inhibit/Enable: A signal (typically TTL/ Master/slave configurations provide higher output thalate) often used as an insulator in the design CMOS compatible) used to turn a power supply power, wider input voltage ranges, synchronized and assembly of power supplies. A registered output on/off. Also called a Remote On/Off. operation, etc. trademark of EI Dupont DeNemours & Co. Long Term Stability: The change, over time, in Maximum Current: When in current limiting the output voltage of a power supply with all other mode, the highest value of output current delivered — N — factors (line, load, temp, etc.) remaining constant, by a power supply. N+1: A redundant power system topology used to expressed as a percentage. This output change is Maximum Load: When running under continu- achieve high reliability levels. The circuit consists of primarily due to component aging. ous operating specifications, the highest amount of a number of power supplies connected in parallel, Low Line: The minimum input line voltage spec- output load allowable for a power supply. sharing the load power. One more supply than is ified for normal power supply operation. See High Maximum Operating Temperature: The necessary to provide full load current is used (i.e. Line and Input Voltage Range. maximum temp. at which a power supply will for a 1200W load, three 600W power supplies are operate to within specified operating parameters. used). Thus, if any single power supply fails, the Low Voltage Directive: (LVD) An EU directive remaining units will continue to power the load. See that covers all electrical equipment with a voltage Normally specified as either ambient or case. Master/Slave and Dual Redundant. ( at the input/output terminals) of 50 to 1,000 VAC Maximum Power : (Pmax) The highest level of N+x: An “N+1” redundant circuit in which more than or 75 to 1,500 VDC. output power that a supply can safely operate at. one extra power supply is used (i.e. N+2, N+3, ...N+x). Lumen: (lm) A lumen is the luminous flux of light Maximum Rating : See Absolute Maximum Nanometer: (nm) A unit of length in the metric produced by an LED that emits one candela Ratings. of luminous intensity over a solid angle of one system, equal to one billionth of a meter. Used as steradian (sr). Mean Time Between Failure: (MTBF) A unit a measure of the wavelength of light. of measure, that gives the relative reliability of a Natural Convection: See Free Convection. Lumen Maintenance: The ability of an LED power supply. MTBF data is either calculated per light to maintain intensity over time. A high power the conditions of MIL-HDBK-217F or demon- Negative Temperature Coefficient: A func- LED will typically retain 70% of its intensity for up strated using actual operating data. MTBF is tion (voltage, resistance, etc.) that decreases as to 50k hours. expressed in hours. temperature increases. Luminance: The luminous flux emitted or re- Mean Time To Repair: (MTTR) For a repairable Neutral: In an AC circuit, the neutral line is the flected from a source; in this case an LED. Given return path for the current provided by the hot wire. 2 power supply, MTTR refers to the average time in candelas per square meter (cd/m ). required to perform the repair work. Encapsulated The neutral line is often connected to ground. See Luminosity Function: Established by the CIE, power modules are typically not repaired. Ground and Hot Line. this function approximates the average visual Metal-Oxide Field-Effect Transistor: Noise: Undesirable variations in the power sensitivity of the human eye to light of different (MOSFET) Power MOSFET’s are used in most supply output that are unrelated to the switching wavelengths. Two functions are defined. The power supplies as the “switch” that chops the frequency. Noise is typically specified as “Ripple photopic luminosity function is used for everyday input signal at very high light levels; while the scotopic luminosity function speeds. They operate at is used for poor light levels. Also called the Lu- high speeds, are efficient minous Efficiency Function. and can handle high power Luminous Efficacy: A measure of the effec- levels. tiveness of a light source in converting electrical Minimum: (min) The low- energy into light. It’s the ratio of luminous flux to est value for a given spec- power & is expressed as lumens per watt (lm/W). ification. Luminous Flux: (F) A measure of the total per- Minimum Load: The ceived power of a light source in all directions. The minimum output load re- measurement factors in the sensitivity of the hu- quired to maintain the nor- man eye by incorporating the luminosity function. mal continuous operating Expressed in lumens. Sometimes called luminous specifications of a power power. See Luminosity Function. supply. Usually associated Figure 20 Modular Construction Page 12 Glossary of Power Conversion Terms and Noise” and given as a peak to peak value Overvoltage: An output voltage that exceeds the with a specified bandwidth. See Electromagnetic specified limit of the power supply. Interference, Ripple and Periodic and Random Overvoltage Protection: (OVP) An output Deviation. monitoring circuit that activates whenever a preset No Load Voltage: The voltage level present at the output voltage level is exceeded. Differing OVP output of a power supply when 0% load is applied. circuits are used, with features that will shut the Nominal Value: An ideal value that is used as a power supply down, “crowbar” the faulty output reference point. Typically it is not the same as the or switch the supply to a different operating mode. value actually measured. — P — — O — Package: The enclosure for a power supply. A Off Line Power Supply: A power supply (linear very wide range of packages are available, ranging or switching) that operates directly off the ac line. from encapsulated modules to large fan-cooled The input voltage is rectified and filtered prior to metal cases. any isolation transformer. Parallel Operation: A power system in which Ohm (Ω): The unit of measurement for resistance. the output currents of two or more power supplies are connected together to provide a higher level of Ohm’s Law: First discovered by the German Figure 21 Oring Diodes output power. A power supply must be designed physicist George Ohm in 1827, the law gives the Output Good: A status (or housekeeping) signal to share output loads to be used in a parallel relationship between the voltage, current and that indicates that the power supply output is pres- connection. Although parallel circuits are used in resistance in a circuit. ent and within a set tolerance. Typically available on redundant systems; power system redundancy is not necessarily achieved through a simple parallel V higher power AC/DC power supplies or distributed I= power systems. connection. See Redundant Operation. R Output Impedance: The ratio of change in Parameter: A specified characteristic or feature Where: I = Current output voltage to a change in output load current. of a power supply. V = Voltage Sometimes referred to as Dynamic Response. R= Resistance Parasitic Capacitance: An unwanted capaci- Output Load: See Load. tance that can introduce undesirable coupling into Open-Circuit Voltage: See No Load Voltage. a circuit. It exists between the components in a Output Power: The maximum output power a Open Frame circuit due to their proximity to one another. Also : A power supply that is made power converter is designed to provide. without an enclosure. Very common in low/medium called stray capacitance. Output Range: A power supply specification that power ac switching supplies, the power supply Passive Component gives the limits over which the output voltage may : A component that is stat- is typically constructed on a printed circuit board ic. For example, resistors, capacitors diodes, etc. which is then mounted in the end-user application. be adjusted and still meet specified performance.

See Enclosure and L-Frame. Output Ripple & Noise: See Noise and Peri- Peak Power: (PP or PPK) The maximum instanta- neous power level that a power supply can handle Operating Life: The number of hours an LED odic and Random Distribution. without damage. is expected to be operational. For illumination ap- Output Voltage: DC voltage level measured at plications where light output is considered critical, the power supply output pins. Peak-to-Peak: (P-P or Pk-Pk) For an AC wave- output degradation to 70% lumens is typically form, the difference between the maximum positive used. For applications where light output is not as Output Voltage Accuracy: The maximum and the maximum negative amplitude of a waveform. critical (such as decorative lighting), 50% is typically deviation (from the ideal or nominal value) allowed Period: (T) The duration of a complete AC cycle. used. Typically given in hours. in the DC output voltage of a power supply. Also called Output Voltage Tolerance, it is expressed as It is given by the formula: Operating Temperature Range: The tempera- a percentage of output voltage. 1 ture range over which a power supply can be safely T= used within specified operating limits. May be spec- Output Voltage Range: The minimum and f ified as ambient, case or base plate temperature. maximum output voltage limits within which a power supply will operate within specified limits. Where: T = Time Optical Coupler: A passive optical component f = frequency in H that passes electronic signals using light waves. Output Voltage Tolerance: See Output Volt- age Accuracy. Periodic and Random Deviation: (PARD) They are commonly used in power supply circuits The noise & ripple voltage superimposed on the to provide very high isolation for feedback lines. Over Current: A current that exceeds the spec- output of a power supply. It is typically expressed in signals. Also called opto-isolator, opto-coupler, ified level of a power supply. peak to peak or rms volts over a given bandwidth opto-isolator or photo-coupler. Over Current Protection: See Current at full load. Oring Diodes: Diodes, typically placed externally Limiting. Photovoltaic Cell: A semiconductor diode that in the output circuit of two power supplies con- Overload: A condition under which excessive converts visible, infrared, or ultraviolet light into nected redundantly to a load. The diodes isolate electric current. The diode consists of a flat P-N each power supply from the other, insuring that one power is drawn from the power supply. May lead to a fault condition. See Current Limiting. junction in a transparent package so that radiant supply provides load power at a time. energy can will fall on the P type silicon. Also called Overload Protection Outage: A loss of power to a circuit or system. : See Current Limiting. a Solar Cell. Overshoot Output Capacitance: When a power supply is : A momentary change in output Pi Filter: A filter consisting of two capacitors off, the capacitance present between the output voltage that exceeds specified limits. A transient connected in parallel with a series inductance. terminals. overshoot will typically occur when a power supply Often used in DC/DC converters to reduce input is turned on/off; or with a step change in output reflected ripple current. Output Current: (Io) The current provided by load or input line. a power supply to the load. See Input Current. Pin-Out Diagram: A diagram that shows the Over Temperature Protection: A fault pro- pin location and functionality for a power module. Output Current Limiting: See Current tection circuit that reduces the output power or Limiting. shuts down the power supply if the operating Plate: See Base Plate. Output Filter: A circuit that attenuates noise and temperature exceeds a set limit. Typically available Point of Load Regulators: See Switching ripple current present on a power supply output. on higher power AC/DC power supplies. Regulators. Normally, a power supply will include internal Over Temperature Signal: A status (or house- Post Regulation: A power supply output circuit output filtering. For critical applications, external keeping signal) that indicates the power supply has that uses a linear regulator to reduce output ripple filter components may be added. shut down due to an over temperature condition. and noise and improve line/load regulation. On the Output Device: See Load. Typically available on higher power AC/DC power negative side, post regulation adds expense and supplies or distributed power systems. degrades power supply efficiency. Output Efficiency: See Efficiency.

MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM Potentiometer: A variable resistor used as an output voltage trimmer. Some power supplies allow the output voltage to be trimmed (typically by about ±10%). The trimmer may be built into the power supply (typical for AC/DC supplies), or it may have to be added as an external circuit by the user (typical for DC/DC modules. Potting: See Encapsulation. Potting Material: See Encapsulant. Power: See Output Power. Power Cycling: A quality assurance test some- times applied to power supplies. For the test, power supplies are operated at full load, at an elevated temperature. The power to the units under test is then cycled on/off. This test will stress the power supply at significantly higher levels than the Figure 22 Simplifi ed PWM Circuit more typical burn in. For commercial grade power devices a burn-in at full load is more common. Power Supply: See Converter (AC/DC) and Pulse Width Modulation: (PWM) A circuit Converter (DC/DC). used in power supplies to regulate output voltage. Power Density: The ratio of power supply Regulation is achieved by varying the conduction output power to the volume of the power supply, Power Surge: See Surge. 3 time of the transistor switches. expressed as watts per in . Power Transformer: See Transformer. Puncture Voltage: See Breakdown Voltage. Power Derating: See Derating. Primary Circuit: The input side of an isolated Push Pull Converter power supply. See Secondary Circuit. : A power supply circuit Power Dissipation: (PD) See Internal Power that uses two transistor switches and a center Dissipation. Primary Current: The current flowing in the pri- tapped transformer. Normally configured as a Power Factor: For an ac input power supply, the mary winding of the power transformer of a power forward converter, the transistor switches turn ratio of true input power to apparent input power. supply. Also called Transformer Input Current. on and off alternately. See Boost Regulator, A measure of the input current that is in phase See Secondary Current. Buck Regulator, Bridge Converter, Flyback with the input voltage (and thus contributing to Primary Voltage: The voltage across the primary Converter, and Resonant Converter. the average power). winding of the power transformer. Also called Trans- Power Factor Correction: (PFC) A power sup- former Input Voltage. See Secondary Voltage. — Q — ply feature in which the ac input current is forced to Primary Winding: The input winding of the Qualification Testing: Testing done on com- be approximately in phase with the input voltage. power transformer. See Secondary Winding. This reduces the harmonic distortion of the power ponents to insure they meet the requirements of system and increases the useful power drawn from Printed Circuit Board: (PCB) A “board” made the product design. the mains. PFC circuits can be active or passive. up of copper layers (sheets) that are laminated Quality: The degree to which a power supply See Power Factor. onto a non-conductive substrate. For power conforms to it’s specifications. supplies, the substrate is typically rigid and uses Power Fail Signal: An output signal (typically FR4 glass epoxy to provide insulation. A pattern Quality Assurance: (QA) A systematic method TTL compatible) that indicates the DC input to of conductive tracks (traces) and pads are etched of monitoring the material, production, testing the power supply has failed. This housekeeping onto the board to provide the wiring interconnec- and packaging of a power supply to insure that signal is typically used to trigger the execution of tions required by the circuit. If the complexity of quality requirements have been achieved and an orderly shutdown during the hold-up time of the power supply design requires it, the board maintained. the power supply. can be made with multiple levels of conductive Quality Control: (QC) The inspection of incom- Power Good Signal: A status (or housekeeping) connection patterns. The vast majority of power ing material, manufacturing processes, and prod- signal that indicates the primary DC output of a supply designs require this type of circuit board. uct testing operations to ensure that a product power supply is still present. Often brought out to Some low power products are available deigned conforms to it’s specifications. a system front panel as an LED indicator. without a PCB. In these designs the circuit com- ponents are mounted onto a pin frame. Quasi-Regulation: Auxiliary outputs on a Power Ground: For a system or circuit, the multiple output power supply that are regulated power supply ground. Process Control: The use of specific, well de- via the primary output (which is controlled by a fined and testable steps to design, manufacture Power Loss: See Internal Power Dissipation. direct feedback loop). Auxiliary output voltages are and store products. The use of continuously tested set by the turns ratio of the isolation transformer. Power Rating: The specified power available at controls results in products that have a consistently Quasi-regulated outputs are significantly affected the power supply output pins. high level of quality; mechanically and electronically. by variations in the primary output. Sometimes Industry standards, such as ISO 9000 are often Power Source: A device or system that supplies referred to as semi-regulation. used to insure that the repeatable quality output of electrical power. This could be a generator, PV a process is achievable and maintained. Quarter Brick Converter: A standard package system, battery, power supply, etc. size for high power density DC/DC converters. A quarter brick typically measures about 1.45 x 2.3 Inches (37 x 58 mm). There is some variance between manufacturers. Other established pack- 1 1 age standards include full, ½, ⁄8, and ⁄16 bricks. — R — Rack: An upright frame for holding electrical equipment or systems. They are typically paneled to create an enclosure that can then be used to provide the mechanical support, power distribu- tion, temperature control, and cable management required for complex systems. Radiation Cooling: The transfer of heat be- tween two materials at different temperature levels. Radiant heat does not play a significant role in the cooling of distributed power systems. Figure 23 Simplifi ed Push Pull Circuit

Page 14 Glossary of Power Conversion Terms Radio Frequency Interference: (RFI) See Reflected Ripple Current: See Input Reflect- Remote Shutdown: See Logic Inhibit/Enable. Radiated EMI (under Electromagnetic Inter- ed Ripple Current. Reset: After a fault condition has shut down a ference). Regulated Power Supply: A power supply power supply, power supply has been shut down Random Noise: See Noise. whose output is held to within a tight error band by a fault condition, the manual operation or the Range Capacitor: See Trimmer Capacitor. regardless of changes in line and load. automatic signal that will restart it. Regulation Resin Range Resistor: See Trimmer Resister. : The ability of a power supply to : A natural or synthetic organic substance maintain an output voltage to within specified limits that’s polymeric in structure. Epoxy resins are Rated Output Current: The maximum output under varying conditions of input line and output used extensively in electronics for potting/molding current that can be continuously drawn from a load. See Linear Regulation. compounds, PC boards, insulators, etc. power supply under specified conditions. Regulator: A circuit or component with a Resistance: (⍀) The opposition to current flow. Reactance: (x) The opposition to the flow of varying input voltage that maintains a tightly Resistance is given in ohms and is equal to: alternating current or voltage due to the presence controlled output voltage. They are often used E of inductance and/or capacitance in the circuit to provide tighter regulation on power lines to R = or component. Inductive reactance causes the critical portions of a circuit or to components I AC voltage to lead the current, while capacitive sensitive to power line fluctuations. They are reactance causes the voltage to lag the current. sometimes called point of load (POL) regulators. Where: I = Current Reactance is specified in ohms. See Linear Regulator, Switching Regulator, E = Voltage R = Resistance Reactive Current: That portion of alternating and Voltage Regulator. current that is not in phase with the voltage. Regulator Diode: A semiconductor diode, Resistance Drop: The voltage drop across a resistor,or the inherent resistance of a component. Reactive Load: A load that is primarily capacitive typically a zener, used as a two-terminal voltage or inductive, rather than resistive. regulator. Resistive Load: A power supply load that exhibits the characteristics of a pure resistance. Reactive Power: (Q) Measured in volt-amperes Regulatory Agencies: Organizations (both reactive (var), the reactive power of a circuit is equal independent and government supported) that Resistive Losses: Losses resulting from the to apparent power multiplied by the sine of the develop specifications and/or test power supplies resistance of a circuit or component. Typically, they phase angle (␾ ) between the circuit voltage and to specifications that define product performance are lost as heat. or intrinsic safety. current. It is given by the formula: Resistor: A very common component, that pres- Q = Irms x Vrms x (Sine ␾) Reinforced Insulation: Insulation that by itself, ents resistance to current flow and lower voltage provides the same degree of protection from levels in a circuit, as well as a variety of other uses. Rectification: The conversion of alternating shock as double insulation. See Basic Insula- Resistors are passive components, typically having current into pulsating DC by using diode rectifiers tion, Double Insulation, and Supplementary two terminals. They are fabricated from a number as switching elements. See Bridge Converter. Insulation. of materials including carbon, metal film, wire and Rectified AC Current: The unfiltered DC Relative Humidity: (rh) The ratio of the amount foil. They are available over a wide range of resis- output of a rectifying circuit. It consists of the of moisture in the air to the amount the air could tance values and power ratings. Variable resistors unidirectional half cycles passed by the full or half contain at a given temperature, expressed as a are also available in a range of values and physical bridge rectifiers. There is one pulse/cycle for a half percentage. A common environmental specifica- configurations. wave rectifier and two pulses/cycle for a full wave tion for power supplies is the ability to withstand Resonant Converter: A power supply topol- circuit. For an illustration of a full wave rectifier, see high levels of relative humidity. ogy in which a resonant tank circuit operating at Bridge Converter. Relative Power: A power level that is specified very high frequencies is used to transfer energy to Rectifier: A circuit that converts alternating with respect to a reference power level. the output. Often found in higher power DC/DC current into pulsating direct current. Used on the converter applications. Reliability: The dependability of a power con- front end of AC power supplies (typically a full wave Response Time: See Transient Recovery Time. rectifier). See Bridge Converter. version product to operate to specified conditions. Restriction of Hazardous Substances: Recovery Time: The time required for a mea- Reluctance: (R) The opposition to the set up of (RoHS) A European directive that sets limits on sured parameter to return to within specified limits a magnetic field in a magnetic circuit. It is compa- the concentration levels of 6 substances. They following an abnormal variation. rable to resistance in electronic circuits. are Mercury, Lead, Cadium, Chromium VI, poly- Redundant Operation: Power system config- Remote Sensing: An external output connec- brominated biphenyls (PBB), and polybrominated uration used to increase system reliability. Often tion wherein sense leads connected to the output dihenyl ether (PBDE). used in distributed power systems, to achieve load provide feedback to a power supply. Used Return: The common terminal on the output of redundancy, power supplies are connected in to compensate for voltage losses caused by the a power supply. It is the return current path for the parallel (typically configured in an “N+1”, dual resistance of long leads or traces to the load. See output. See Common. redundant or master/slave architecture). Local Sensing. Reverse Current: See Leakage Current. Reverse Voltage Protection: A power supply feature that protects internal components from damage in the event a reverse voltage is acciden- tally applied to either the input or output terminals. Ripple and Noise: See Periodic and Random Deviation (PARD). Ripple Voltage: The periodic AC component imposed on the output voltage of a power supply. Typically specified as part of “Ripple & Noise” and given as a peak to peak value over a specified bandwidth. See Periodic and Random Devi- ation (PARD). Room Temperature: A term sometimes used to describe a benign operating environment. Al- though it typically implies a temperature of about 77°F (25°C), room temperature has no actual quantitative meaning.

Root Mean Square: (rms) For a sine wave, the rms value is equal to:

rms = 0.707 x IPEAK Fig 24 Simplifi ed Remote Sensing Circuit MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM Short Circuit Current: The current that flows when the output is directly shorted. Short Circuit Protection: A circuit that limits or reduces the output current of a power supply if the output is shorted. See Current Limit and Foldback Current Limit. Shunt Regulator: A linear regulator placed in parallel with the load to achieve a constant voltage across the load. See Linear Regulation, Post Regulation and Series Regulator. Sine Wave: See Alternating Current and Alter- nating Voltage. Single Ended Circuit: A circuit that has one end grounded. Also called an Unbalanced Circuit. Single Ended Input: A power supply input that has one side grounded. Also called an Un- balanced Input. Single Ended Output: An output circuit with one line grounded. Also called an Unbalanced Output. Fig 26 Simplifi ed Series Connection Sink: A circuit (or device) into which current Royer Converter: A self-oscillating push-pull line losses incurred when powering a load some drains. switching topology often used in low cost, low distance from the power supply. See Remote Six-Sided Shielding: A packaging technique power DC/DC converter designs. Also called the Sensing and Local Sensing. in which the power supply is placed into a metal classical converter. Sense Resistor: A resistor used to sense the case. The metal shielding minimizes noise radia- current flowing in a circuit. The voltage drop tion from the switching components of the power — S — across the resistor is measured and the circuit supply. A continuous shielded case has the base Safety Compliance: Certification that a power current (which is proportional to the measured (or header) welded on, further reducing potential supply (or family of power supplies) has been voltage) is derived from this measurement. Care noise leakage from the power supply or preventing approved by a safety agency such as UL, TUV, must be taken not to cause significant power circuit noise from interfering with the supply. losses. So typically the sense resistor will be small. CSA, VDE, etc. Slave: A power supply that has no internal feed- Safety Extra Low Voltage: (SELV) A term used Sensor: A circuit or device that detects a system back loop. The output regulation of a slave unit by safety and regulatory agencies to describe the or environmental phenomena and produces a is controlled by a master power supply to which highest voltage level that can be contacted by a current or voltage that is proportionate to this its’ operation is synchronized. Sometimes called person without causing injury. It is currently defined measurement. This output is then used to display a “booster” See Master. the current state of the phenomena (current tem- as 60 VDC (42.4 Vpk). Slow-Blow Fuse: A fuse that uses a wire that perature, flow rate, etc) and/or start some type of breaks apart slowly. The time delay allows the Safety Ground: A conductive path to earth alarm or control action. ground designed to protect equipment operators fuse to withstand transient current surges that from potential electrical shocks. Series Operation: A power system configu- would not damage the circuit. A fast blow fuse ration in which multiple isolated power supplies would open, shutting down the circuit needlessly. Sample: A quantity of products, components, are configured to obtain a higher output voltage Snubber: A component or network that reduces etc taken from a larger group for the purpose of level (inputs connected in parallel) or wider input the voltage rise and potential voltage overshoot in verification testing. The sample size is set at a voltage range (inputs connected in series) than a power supply switching circuit. number high enough to statistically represent the that obtainable from one power supply. larger group for the parameter under test. Socket: A connector or slot (typically female) Series Regulator: A linear regulator placed in fixture into which a power supply or component Schematic (Diagram): A diagram that illustrates series with the load to achieve a constant voltage inserted. It allows easy connection/removal of an electronic circuit. It will show components and across the load. This is the most popular method systems or components to a circuit. interconnections. Components are typically with of linear regulation. See Linear Regulation, Post an abbreviation of their type and a number (R1, Regulation and Shunt Regulator. Soft Start: A power system input circuit that limits C3, etc). Sometimes component values are also the inrush current at turn on. given. Also called a Wiring Diagram. Set Point Accuracy: The ratio of the actual output voltage of a power supply to its specified Solar Array: A complete, power generating unit. Secondary Circuit: The output side of an iso- output voltage. An array consists of any number of Solar panels. lated power supply. See Primary Circuit. Panels can be added or subtracted to fit the needs Setting Accuracy: See Set Point Accuracy. Secondary Current: The current flowing in the of the installation. Shelf Life: The longest period of time that a pow- secondary side of the isolation transformer of a Solar Cell: See Photovoltaic Cell. power supply. Also called Transformer Output er supply could be stored before deterioration of Current. the components or operating performance occurs. Solar Energy: Energy derived from the sun. Typ- ically refers to energy captured over a given period Shock Hazard: A condition that presents the dan- Secondary Output: See Auxiliary Output. of time within a specific surface area. ger of electric shock to a person. Secondary Power: The power in the secondary circuit of a transformer. Also called Secondary Short Circuit: A power sup- kVA (or VA). ply fault condition in which the positive rail of the output Secondary Voltage: The voltage across the becomes directly connected primary winding of the power transformer. Also to the negative rail. If the pow- called Transformer Output Voltage. See Sec- er supply has “Short Circuit ondary Voltage. Protection”, it will immediately Secondary Winding: The output winding of the limit the output current to pre- power transformer. Sometimes called Secondary vent damage to the supply. If Coil. See Primary Winding. there is no protection, a short of more than one or two sec- Sense Line: An input to the power supply that onds would likely damage the “senses” the output voltage level at the load. Used supply. See Current Limit and in remote sensing connections to compensate for Foldback Current Limit. Fig 27 Shielding Page 16 Glossary of Power Conversion Terms Solar-Energy Conversion: The process of Stiff Line: A condition wherein there is no signif- the input voltage is switched or “chopped” in a changing solar radiant energy into electric power. icant impedance present on the AC input mains. power supply. Sometimes called Frequency of Solar Module: A number of solar cells that have The input voltage to the power supply under these Operation. been connected in series or parallel and then conditions will not change appreciably with load. Switching Power Supply: A power supply that encapsulated into a weatherproof module. The Still Air: A power supply operating environment in uses switching regulation. Switchers are typically module typically includes a tempered glass cover which the surrounding air restricted. Often occurs in smaller, more efficient and lighter than linear supplies. and aluminum frame. small enclosures (sometimes sealed) where air can- Switching Regulator: A circuit (typically a pulse Solar Panel: A panel that consists of a number not move freely. Because it does not have sufficient width modulator) that uses a closed loop design to of solar modules connected together. A panel is a mass or flow, still air is prone to thermal runaway regulate the output voltage. field installable unit. caused by the thermal output of the power system. Symmetrical Wave: A wave with positive and Storage Life Solar Power: The usable electricity generated : See Shelf Life. negative half-cycles that are identical in shape by solar cell based systems. Storage Temperature Range: The range of and amplitude. Solder: A metal alloy that is melted to join two ambient temperatures over which a power supply System: A set of components, hardware and/ other metals electrically and mechanically. Originally, can be safely stored. See Operating Tempera- or software that operate together to meet an end most solders used combinations of lead and tin. In ture Range. purpose. 2006 the European Union prohibited the use of ex- Stress: A mechanical or electrical strain or tension cess lead in consumer electronics. Since then, lead on a component or circuit. free solders have typically been used in electronics. Subassembly: A complete circuit or assembly — T — Solderless Connection: An electrical con- that is part of a larger unit. Tail: Typically used to describe the current that nection made without using solder. Typically continues to fl ow in a circuit when a semicon- Supplementary Insulation: Insulation applied ductor switch has been closed. Dealing with tail it is a connection between two leads made by in addition to (and independent of) basic insulation. current is very important consideration in the crimping, splicing, or wire wrapping. Also called Supplementary insulation provides protection design of very high power/high speed switching Wire Wrapping. against electric shock in case the basic insulation circuits. Also called Current Tail. Source: The battery, generator, power mains, etc, fails. See Basic Insulation, Double Insulation, Tantalum: (Ta) A material used in some electro- that provides the input power to a power supply. and Reinforced Insulation. lytic capacitors (rather than aluminum). Tantalum Source Effect: See Line Regulation. Surface Mount Devices: (SMD) Components capacitors are widely available, have high reliability (including some power supplies) designed to be and high efficiency. The primary drawback of tan- Spacing: See Clearance Distance and Creep- talum’s is expense. age Distance. assembled using surface mount technology. Surface Mount Technology Technischer Uberwachungs-Verein: (T.U.V.) Specifi c Power: See Power Density. : (SMT) An auto- mated manufacturing process in which compo- A group of independent companies that provide Specifi cation: A listing of a products’ perfor- nents are designed for mounting on the surface of safety testing (and project management & con- mance capability (and limitations) for a variety of a substrate or PC board. Often used in the design/ sulting) in a number of industries. For the power parameters. Usually given as minimum, typical assembly of low power DC/DC converter modules. supply industry they are mainly and/or maximum limits in a “datasheet” format. used to validate product design Surge: A sudden rise in the flow of current or and operation to VDE and DIN Spike: A sharp current or voltage pulse (or voltage. This often happens when power supplies standards. transient) of very short duration. Often, a power are initially turned on as circuit capacitors charge. supply will require protection on the input line to Some fault conditions could also cause a surge. A Temperature: (T) See Ambient Temperature. prevent damage from transients. significant surge could cause damage to a power Temperature Coefficient: The average change Split Bobbin Winding: A transformer winding supply if proper protection is not placed on the in power supply output voltage per degree centi- technique in which the primary and secondary input (such as an MOV). grade. Expressed as a percentage over a specified windings are wound on a bobbin side by side Surge Current: See Surge. temperature range. with an isolation layer in between. See Bobbin. Temperature Derating: See Derating. Surge Suppressor: A semiconductor device Stability: See Long Term Stability. that will block or short to ground potentially de- Temperature Effect: See Temperature Co- efficient. Standard: An industry wide specifi cation that de- structive transients or voltage spikes on the input tails the performance characteristics, physical size, line to a power supply. Sometimes called a Surge Temperature Range: See Operating Tem- operating environment, and testing requirements Protector. perature Range and Storage Temperature that must be passed to meet a particular level of Surge Voltage: See Surge. Range. performance. to meet a specifi c level of etc of a de- Switch Temperature Scale: The scale graduated in vice or system. Often a standard will defi ne a subset : A circuit or device used to open or close a circuit. For instance, in a power supply, semicon- degrees, from which a temperature is read. The of a device or system performance, such as EMI/EFI different scales include centigrade, Fahrenheit, or the requirements to meet various levels of safety. ductor “switches” (typically MOSFET’s) are used to chop the the input into pulses. Rankine, absolute, reamur and kelvin. The kelvin Standby Current: The input current drawn by scale is the same as the absolute scale. For the Switching Frequency a power supply when it has no load and has been : The rate at which power supply industry, the Celsius or centigrade shut down by a remote ON/OFF signal. Standby Power: The power dissipated by a power supply when it has no load and has been shut down by a remote ON/OFF signal. Stand-Off: A mechanical support post (typically an insulator) used to hold a wire, component or PC board away from a chassis or base. Start-Up Delay: After input power is applied to a power supply, the delay that occurs before the output voltages are within regulation. Static Load: A load that remains constant for a specified period of time. Typically specified as a percentage of full load. Status Signals: See Flag Signal. Step Change: A sudden change in a power supply parameter. Normally used when referring to changes in output load or input line during power supply testing. Fig 28 Surface Mount DC/DC Converters MicroPower Direct We Power Your Success - For Less WWW.MICROPOWERDIRECT.COM and Fahrenheit scales are used. Also called the Thermometer Scale. Temperature Shock: See Thermal Shock. Tertiary Winding: A third winding on the power supply. It is typically used in a forward converter configuration to “reset” the transformer at the end of each cycle. Occasionally tertiary windings are used to provide a third, independent output voltage. Sometimes called an Energy Recovery Winding. Terminal: A connection point on a power supply consisting of a screw terminal. These come in strips with multiple connections (typically two to ten). Terminal Block: A group of several terminals, mounted on a solid insulating block with a solid between each pair of terminals. Typically used on medium to high power AC/DC power supplies and chassis mount DC/DC converters. Sometimes Fig 29 Typical Bench Test Set-Up called a Barrier Strip. between the base plate/chassis of a power supply Thermal Shock: A test to identify the effects Test: A procedure during which the performance, module and heatsink as well as insuring high ther- of applying heat or cold to a power supply very or a particular part or the performance, of a power mal conductivity across the junction. See Thermal rapidly. The rapid temperature change causes dif- supply is verified. Joint Compound. ferent parts of the supply to expand and contract differently. These changes could be catastrophic Test Instrument: A device, such as an oscillo- Thermal Conductivity: For a given material, if the supply has not been designed correctly. scope or voltmeter, used for checking the operation the time required for heat to transfer (via con- of a power supply. duction) across a unit material thickness of 1 Thermistor: A component that changes resis- Test Point: A terminal, pad, etc that is used to meter when the temperature differential of the two tance with temperature. They are available with connect test equipment o various measurement opposite faces is 1K. Given in joules per second either a positive or negative temperature coeffi- points within a circuit. per square centimeter. cient of resistance. In power supplies, they are often used (ones with a negative temperature Thermal Gasket: A flexible pad or wafer that Test Probe: A thin pencil-like instrument with a coefficient) in inrush current limiting circuits. pointed metal tip. When connected to a meter or is placed between a power supply baseplate/ scope, etc, it is used to take readings at various chassis and a heatsink. Thermal gaskets have a Thermocouple: A sensor that is used to mea- points within the power supply circuit. very low thermal resistance, insuring high thermal sure temperature. Essentially, it consists of two conductivity across the junction. Use of a ‘dry’ wires welded together at one end. The wires Thermal Adhesive: An epoxy (rather than oil) gasket may eliminate some problems associated are different metals, so when the junction area is based thermal joint compound. When cured, with thermal joint compounds (inconsistent coat- exposed to a change in temperature, a voltage is thermal adhesives provide a mechanical bond ing, contaminants, etc.). Gaskets are available in produced. Using reference tables, the temperature a number of standard pre-cut forms. at this point v=can be calculated. Thermal Grease: See Thermal Joint Com- Three Terminal Regulator: A linear regulator pound. packaged in a standard 3-terminal transistor pack- age. These devices can be configured as either a Thermal Joint Compound: A fluid or paste that shunt or series regulator. is spread between a power supply baseplate\chas- sis and a heatsink. Normally, compounds consist of Tin: (Sn) A metallic element used in solder and (in a silicon or synthetic oil that carries a low thermal foil form) as the the plates of a capacitor. resistance filler (aluminum, etc.). The compound Tolerance: The amount of variation that is allowed fills the voids caused by irregularities in the mating in the specifications of a power supply or component. surfaces insuring high thermal conductivity across the junction. Topology: The layout and circuit inter connections that make up the characteristics of the different Thermal Resistance ␪ : ( ) A measure of the types of a power supply. Major power supply topol- opposition a material will have to the flow of ogies include Flyback, Forward, Buck, Boost, etc. heat. Used to calculate the temperature drop that occurs when power flows through a material or Toroid: See Toroidal Coil. across the junction of two materials. Given in units Toroidal Coil: A coil wound on a donut shaped of degrees Celsius per watt (°C/W). core. The core is made of powdered-iron or ferrite. Thermal Resistivity: (␳) A measure of the ability Widely used in power supplies, toroidal coils have of a material to impede the flow of heat. Typically certain advantages including a higher Q factor and given in units of (°C)(T)/W, where T equals the better isolation properties. A disadvantage is that thickness of the material and W equals the power an air core is not practical. flowing through the material in watts. Tracking: For a multiple output power supply, Thermal Runaway: A circuit condition in the parameter that gives the change in one output which an increase in the ambient temperature voltage caused by a change in the voltage level or surrounding a power supply causes an increase load on another output. in the internal power dissipated. This increases Transformer: A device that uses electromagnetic the case temperature, which in turn increases the induction to transfer electrical energy from one circuit ambient temperature of the surrounding air. The to another, without a direct connection between spiraling effect of these temperature increases will them). A transformer includes a common core with eventually lead to failure of the power system. This separate primary and secondary coils wound on it. condition occurs when inadequate measures (air When an alternating current is applied to the primary flow, system venting, power derating, etc.) are winding, the resulting magnetic flux in the core in- taken to get heat away from critical components. duces an alternating voltage across the secondary Thermal Protection: A protection feature winding. The induced voltage in the secondary will that shuts a power supply down if its internal cause a current to flow in an external circuit.

temperature exceeds a preset limits. Also called Transformer Coupling: The inductive coupling Fig 30 Thermal Resistance thermal shutdown. of energy through a transformer.

Page 18 Glossary of Power Conversion Terms Transient: A spike or step change in a power Unbalanced Output: See Single Ended Winding: A wire coil wound around a magnetic supply parameter. Commonly used in describing Output. core. Used in the fabrication of inductors and transformers. input line and output load characteristics. Unipolar Transistor: See Field Effect Transient Recovery Time: The time required Transistor. Wire: A metal strand or thread used as a con- for a power supply output to return to within spec- ductor. ified limits following a step change in output load Wire Bonding: A method of using very fine wires current. Expressed as a percentage of rated value. — V — to make interconnections between a semiconduc- Transient Response: A power supply’s ability to Variable Resistor: See Potentiometer. tor device and it’s packaging. The wires are welded return to a constant output voltage level following Varistor: A component with a nonlinear resistance (the process is also called bonding) at both ends a step change in output current. that varies with the applied voltage. Typically, the using a combination of pressure, heat and ultra- sonic energy. This fabrication method is also used Transistor: See Bipolar Junction Transistor. varistor has a very high resistance at low voltages. The resistance decreases as the voltage increases. in the manufacture of some high reliability power Trim: To make a fine adjustment. Trim circuits are They are often used in power supply input circuits products that use hermetically sealed hybrid cases. typically used to vary power supply outputs by a to protect against excessive transient voltages. Wire Gauge: See American Wire Gauge and small amount (typically ±10%. They are sometimes called a Voltage Dependent Birmingham Wire Gauge. True Power: The actual power consumed by an Resistor (VDR). Withstand Voltage: The maximum voltage ac circuit. Verband Deutsher Electrotechniker: level that can be applied between circuits or Turn-Off Time: The time required for the oper- (V.D.E.): A German association components without causing a breakdown. See ation of a power supply to completely cease after that sets standards for product Breakdown Voltage and Isolation. input power is removed. Also applies to the time safety and noise emissions; and it takes to stop after a remote off signal has been tests and certifies products to those received (on power supplies that have remote On/ standards. — X — Off capability. Vibration: A continuous shaking or oscillating X-Axis: The horizontal axis on a chart or graph. Turn-On Time: The time required for the oper- movement. Industrial power supplies are some- X Capacitor: In an EMI filter, x capacitors are ation of a power supply to start after input power times tested for their ability to withstand the stress placed across the input line. If an x-capacitor fails, is applied. Also applies to the time it takes to start of sustained vibration without damage. the risk is equipment damage and even fire. X after a remote on signal has been received (on Voltage Balance: For a multiple output power capacitors come in three categories that reflect power supplies that have remote On/Off capability. supply, the percentage difference in voltage level their impulse test ratings. These are X1, X2 and between two outputs with opposite polarities and X3. See Y-Capacitor. — U — equal nominal values. Undershoot: A transient change in a power Volt Ampere: (VA) The product of the circuit volt- — Y — age (in Volts) and current (in amperes). It is the unit supply output voltage that does not meet the Y-Axis: The vertical axis on a chart or graph. lower limit of the voltage accuracy specification. for expressing the apparent power in an AC circuit. Typically occurs at the power supply turn on/off See Apparent Power. Y Capacitor: In an EMI filter, y capacitors are or with some step change in output load or input Voltage Clamp: See Clamp Diode. connected from the input line to the chassis. If a line. See Voltage Accuracy. y-capacitor fails, there is a shock risk to the user. Voltage Divider: A resistor network (or ladder) Y capacitors come in four categories that reflect Underwriters Laboratories: (U.L.) An inde- that divides a voltage applied to it by a desired their impulse test ratings. Y1, Y2, Y3 and Y4. See pendent, organization that con- amount. X-Capacitor. ducts safety testing of products to Voltage Doubler: A power-supply circuit that established standards. takes an AC input voltage and supplies a DC output Undervoltage Protection: A protection circuit voltage of about twice the peak value. —Z — that shuts a power supply off if the output voltage Zener Breakdown: A condition that occurs Voltage Drift: See Drift. falls below a preset level. Sometimes used as an in a semiconductor junction when the reverse input protection circuit in wide input range power Voltage Limit: The specified maximum or mini- bias voltage exceeds a certain value (this value supplies (AC and DC) to prevent overheating if the mum values of a voltage range. varies with different diodes). If the electric field at the junction becomes strong enough, current will input voltage sags below a predetermined level. Voltage Regulation: See Regulation. Sometimes called Undervoltage Shutdown or flow in the opposite direction. Some diodes are Undervoltage Lockout. Voltage Regulator: A circuit or device that pro- fabricated to avalanche at precise voltages. Also vides a steady output voltage despite variations in called Avalanche Breakdown. Uninterruptible Power Supply: (UPS) A the output load or the input line. They are readily power supply that will continue to operate after available as linear or switching regulators. As the Zener Diode: A diode specially fabricated to the loss of ac input power. A UPS normally uses names imply, they use linear or switching regula- conduct in both directions. It conducts in the some type of automatic battery backup system. tion circuits. They are also called Point Of Load forward direction like a normal diode, and once a Universal Input: An AC input to a power sys- regulators because they are often used very close set voltage level is met, it will conduct in reverse tem that accepts all the standard voltage levels to the load they are powering. In power supply circuits they are typically used as available from AC mains. Typically specified at 85 voltage regulating devices. Also called an Ava- VAC to 265 VAC. — W — lanche Diode or Zener. Unregulated Power Supply: A power supply Zener Knee: The transition point on a graph whose output will rise and fall with the input line Warm-Up Drift: See Drift. of the voltage characteristics of a Zenor where voltage. The output voltage regulation is typically Warm-Up Time: The time required for a power the diode goes into avalanche breakdown. For specified as a percentage of the percentage change supply to operate to within specifications after voltage regulation circuits, the knee should be as in the input voltage (%/%VIN). Low power DC/DC turn-on. This time normally precedes a long-term sharp as possible. converters (1 & 2W) are often unregulated designs. drift specification. Unshielded Cable: A cable that does not have Watt: (W) The unit of electric power. A one ohm MicropPower Direct offers well over 5,000 a shielding jacket. These cables are susceptible resistor with a current of one ampere flowing AC/DC power supplies, DC/DC converters, to interference from stray circuit noise. They could through it will dissipate one watt. AC & DC LED drivers, IGBT drivers and POL also radiate noise into the surrounding circuits. switching regulators. Unshielded Transformer: A transformer that Wattage Rating: The specified output power does not have a protective cover or shielding. of a power supply. Typically given as a maximum. Visit micropowerdirect.com or call today Unbalanced Circuit: See Single Ended Cir- Wave: a single cycle of an AC waveform. (781-344-8226) for full datasheets; a low cost quotation; or free samples. cuit. Weight: The force of the gravitational pull upon Unbalanced Input: See Single Ended Input. a power conversion product. Typically given in ounces and grams.

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