DOCSLIB.ORG

MOSFET Power Losses and How They Affect Power-Supply Efficiency

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
MOSFET Power Losses and How They Affect Power-Supply Efficiency Electronics Technical MOSFET power losses and how they affect power-supply effi ciency by George Lakkas, Texas Instruments Power-supply efficiency is a critical criterion for today’s cloud-infrastructure hardware. The efficiency of the chosen power solutions relates to system power loss and the thermal performance of integrated circuits (ICs), printed circuit boards (PCBs), and other components, which determine the power-usage effectiveness of a data centre. This article revisits some of the basic principles zero losses, thus offering 100% efficiency. contributors in a buck converter: conduction of power supplies and then addresses how However, components are not ideal, as is losses, switching losses, and static (quiescent) MOSFETs – the power stage of any switching- illustrated in the following examples. losses. voltage regulator – affect efficiency. For the An efficient switching regulator results in less MOSFETs have a finite switching time, linear regulator shown in Fig. 1, power loss heat dissipation, which reduces system cost therefore, switching losses come from the and efficiency are defined by Eqs. 1 and 2. and size for elements such as heat sinks, dynamic voltages and currents the MOSFETs fans and their assembly. In battery-operated must handle during the time it takes to turn (1) systems, less power loss means that these on or off. devices can use the same battery for a Switching losses in the inductor come from longer run time because the device pulls less (2) the core and core losses. Gate-drive losses current from the battery. are also switching losses because they In the ideal switching regulator shown in To consider the various factors that contribute are required to turn the FETs on and off. For Fig. 2, the current is zero when the switch is to efficiency, the focus of this article is on the the control circuit, the quiescent current step-down (buck) DC/DC converter topology, contributes to power loss; the faster the open and the power loss is zero, thus VIN is being chopped. When the switch is closed, which is the most popular switching-regulator comparator, the higher the bias current. For the voltage across it is zero and the power topology in today’s cloud infrastructure the feedback circuit, the voltage divider, loss is also zero. An ideal switch implies systems. Fig. 3 shows the key power-loss error amplifier and comparator bias currents Fig. 1: Typical linear regulator. Fig. 3. Power-loss contributors in a buck switching regulator. Fig. 2: Ideal switching regulator. Fig. 4: MOSFET conduction losses. 42 April 2016 – EngineerIT Fig. 5: MOSFET switching losses. Fig. 6: Switch MOSFET gate losses. Fig. 7: General gate losses. Fig. 8: Total switch MOSFET losses. Fig. 9: Rectifier MOSFET body-diode current. contribute to power loss. Megaohm resistors Relationships for Fig. 5 to derive loss equation: frequency, QGS2 and QGD depend on the cannot be used to reduce power loss time the driver takes to charge the FET, and I E = (V × I /2) × t1, G because of the bias current into the feedback t1 DS D is the gate current. circuit. Fig. 4 shows a basic switching circuit E = (V /2 × I ) × t2, t2 DS D Switch-MOSFET gate losses can be caused and Eqn. 3 is used to calculate conduction P = 2 × (E + E ) × f , by the energy required to charge the MOSFET losses for Q1 or Q2. SW t1 t2 SW gate. That is, the Q at the gate voltage t1 = Q /I , G(TOT) GS2 G of the circuit. These are both turn-on and turn- (3) off gate losses. t2 = QGD/IG, V = Miller plateau, Most of the power is in the MOSFET gate PLAT driver. Gate-drive losses are frequency- VTH = Gate-to-source threshold voltage, dependent and are also a function of the Note that R is the R of the selected gate capacitance of the MOSFETs. When DS(on) I = Cdv/dt, MOSFET, I is the root-mean-square (RMS) G turning the MOSFET on and off, the higher the current through the MOSFET, and that neither Q = C × V, switching frequency, the higher the gate-drive of these is a function of switching frequency. losses. This is another reason why efficiency dt = t1 or t2, and In general, a higher switching frequency and goes down as the switching frequency higher input voltage require a lower QG (gate goes up. VGS(actual) is the actual gate-to-source drive charge) to cut down the switching losses in voltage driving the MOSFET. Larger MOSFETs with lower R provide the switch MOSFET (Q1). DS(on) MOSFET switching losses are a function of lower conduction losses at the cost of higher gate capacitances, which results in For a rectifier MOSFET (Q2), low RDS(on) is most load current and the power supply’s switching higher gate-drive losses. These losses can important, but don’t ignore the gate power. frequency as shown by Eqn. 4. be significant for power-supply controllers Also, changing the MOSFET RDS(on) changes the duty cycle (D), which affects RMS currents (with external MOSFETs) at very high switching frequencies in the multiple-megahertz region. and losses elsewhere. The inductor current (4) There is no known method for calculating also affects MOSFET conduction loss. a “best” QG and RDS(on) in a given situation, The high-side MOSFET (Q1) switching losses although figure-of-merit (FOM) numbers are evaluated first in Fig. 5 because they are where VIN = VDS (drain-to-source voltage), are typically mentioned in data sheets as I = I (drain current), f is the switching more complex. OUT D SW (FOM = RDS(on) × QG). EngineerIT – April 2016 43 Fig. 10: Rectifier MOSFET gate driver and losses. Fig. 11: Total rectifier MOSFET losses. For the switch MOSFET shown in losses (PCON), body-diode conduction losses Fig. 6, a lower gate charge (Q ) in (9b) G (PBD), and gate losses (PGATE). Eqn. 5 enables lower power loss and a faster There are no switching losses because of switching time; however, this contributes to the bodydiode. The body diode conducts (9c) more parasitic turn-on of the rectifier MOSFET. and the voltage across the FET is the A happy medium can be obtained in the diode voltage, which is zero. The body design to accommodate these trade-offs. diode ensures zero-voltage switching per (9d) Eqn. 7. (5) (7) Conduction losses are simple I2R losses There are also general gate losses as shown when the MOSFET channel conducts per in Fig. 7. The MOSFET effect on the gate- Eqn. 8. (9e) driver IC, or a pulse-width modulation (PWM) controller with an integrated gate driver, add to the power-dissipation losses. Eqn. 10 can be used to approximate the (8) body-diode power loss. As shown by Equation 6, gate-drive losses do not all occur on the MOSFET. where: (10) R is the RDS(on) of the selected MOSFET, I is the RMS current through the MOSFET, The final consideration in Fig. 10 is for the (6) t is the delay between the upper DLYUpLo gate losses of the rectifier MOSFET (Q2). Gate MOSFET turning off and the lower MOSFET losses are calculated in the same manner turning on, and where: as with the switch MOSFET. Losses can be t is the delay between the lower DLYLoUp significant because of a higher gate charge. MOSFET turning off and the upper MOSFET PDRV is the total gate drive loss divided to calculate the driver loss, turning on. Fig. 11 shows the various contributors that affect total losses attributed to the rectifier R is turn on of the driver, The rectifier MOSFET also has body-diode GHI MOSFET. losses. The average body-diode current can RGLO is the turn off of the driver, be calculated during dead time. Conclusion Replacing RGHI with RG is the loss in the gate resistor. The blue waveform in Fig. 9 shows the dead The efficiency of a synchronous step-down Replacing RGHI with RGI is the switching FET time, which is the time between when the power converter with integrated or external loss, high-side FET turns off and the low-side FET MOSFETs can be optimised when the (rectifier FET) turns on. We want the average Higher QG increases driver dissipation, and designer understands the parameters that current in the switching cycle. The output affect efficiency and the specifications to Adding external RG reduces internal driver dissipation because it reduces the overall inductor (L) dictates the slope of the dotted look for in data sheets. line, I resistance path to the MOSFET gate. BD1, IBD2, IBD3. This slope is the average current through the body diode. In the absence of an ideal power converter, Fig. 8 shows the various contributors that the designer has to make trade-offs and affect total switch MOSFET losses. Eqns. 9a through 9e can be used to optimise the parameters that affect power- determine the body-diode current: supply efficiency. Now consider the rectifier (synchronous) MOSFET total and conduction losses. Power (9a) Contact Erich Nast, Avnet South Africa, loss in a rectifier MOSFET consists of conduction Tel 011 319-8600, [email protected] 44 April 2016 – EngineerIT.
Load more

Recommended publications
  • What Is an SMPS and How Does It Generate Harmonics?
    MIRUS FREQUENTLY ASKED QUESTIONS FAQ’s___ International Inc. 6805 Invader Cres., Unit #12, Mississauga, Ontario, Canada L5T 2K6 Harmonic Mitigating Transformers <Back to Questions> 4. What is an SMPS and how does it generate harmonics? The Switch-mode Power Supply (SMPS) is found in most power electronics today. Its reduced size and weight, better energy efficiency and lower cost make it far superior to the power supply technology it replaced. Electronic devices need power supplies to convert the 120VAC receptacle voltage to the low voltage DC levels Rectifier Lls that they require. Older generation power supplies used Bridge large and heavy 60 Hz step-down transformers to i convert the AC input voltage to lower values before ac Smoothing Switch-mode rectification. The SMPS avoids the heavy 60 Hz step- vac Capacitor dc-to-dc Cf converter down transformer by directly rectifying the 120VAC Load using an input diode bridge (Figure 4-1). The rectified voltage is then converted to lower voltages by much smaller and lighter switch-mode dc-to-dc converters using tiny transformers that operate at very high Figure 4-1: Typical circuit diagram of Switch-mode Power frequency. Consequently the SMPS is very small and Supply light. The SMPS is not without its downside, however. The operation of the diode bridge and accompanying smoothing capacitor is very non-linear in nature. That is, it draws current in non-sinusoidal pulses at the peak of the voltage Voltage waveform (see Figure 4-2). This non-sinusoidal current waveform is very rich in harmonic currents. Because the SMPS has become the standard computer power supply, they are found in large quantities in commercial buildings.
    [Show full text]
  • EE 462: Laboratory # 4 DC Power Supply Circuits Using Diodes (Lab 3 Report Due at Beginning of the Period) (Pre-Lab4 and Lab-4 D
    EE 462: Laboratory # 4 DC Power Supply Circuits Using Diodes by Drs. A.V. Radun and K.D. Donohue (2/14/07) Department of Electrical and Computer Engineering University of Kentucky Lexington, KY 40506 Updated by Stephen Maloney (2/12/08) (Lab 3 report due at beginning of the period) (Pre-lab4 and Lab-4 Datasheet due at the end of the period) I. Instructional Objectives Design and construct circuits that transform sinusoidal (AC) voltages into constant (DC) voltages. Design and construct a voltage regulator based on the characteristics of the Zener diode. Evaluate the performance of simple rectifier and regulator circuits. See Horenstein 4.3 and 4.4 II. Background Electric power transmits best over long distances at high voltages. Since P = I V, a larger voltage implies a smaller current for the same transmitted power. And smaller currents allow for the use of smaller wires with less loss. The high voltages used for power transmission must be reduced to be compatible with the needs of most consumer and industrial equipment. This is done with transformers that only operate with AC (DC does not pass through a transformer). However, most electronic devices powered by a home outlet require DC (constant) voltages. Therefore, the device must have a power supply that converts AC voltages into a DC (constant) voltage. The terminology "DC" is somewhat ambiguous. DC can mean the voltage or current always has the same polarity but changes with time (pulsating DC), or it can mean a constant value. In this lab assignment DC will refer to a constant voltage or current.
    [Show full text]
  • Custom Power Supplies, Transformers, Chokes & Reactors
    YOUR POWER SOURCE Custom Power Supplies, Transformers, Chokes & Reactors NeeltranThe Story Transformers and Power Supplies • Industry Leader since 1973 Neeltran has become the most reliable supplier of Transformers and Power Supply Systems in the industry. Our engineers, along with our manufacturing team, have the knowledge and ability to meet the special needs of our customers. All power supplies are custom designed to your specifications by our engineering staff and completely fabricated in-house at our manufacturing facility. Our facilities and experience include: • Research & Development Since 1973 Neeltran has been a leading • Test Laboratory manufacturer of transformers and • Design Engineering power supplies. • Printed Circuit Board Manufacturing Our general product range is: • Steel Cutting Machinery • Dry Type and Water Cooled Transformers: • Baking Ovens 5–10,000 KVA (up to 25 KV input) • Vacuum Pressure Impregnation Tanks (Outputs up to 300 KV and 50 KHZ) • Coil Winding Equipment • Oil filled Transformers (Rectifier type only): 100 KVA to 50 MVA (up to 69 KV input) • Painting and Steel Fabrication to manufacture our own enclosures • Oil filled high frequency Transformers: • Assembly Areas up to 50 KHZ, 2000 KVA, up to 50 KV output Industry standards are maintained with our • Cast Coil Transformers: up to 20 MVA testing equipment assuring that all shipped (up to 35 KV input) products meet customer’s requirements and • Chokes and Reactors air or iron: specifications. Impulse testing as well as customer up to 25 KV, 20,000 amps specific testing is available upon request. • Power Supplies: 100 A to 500,000 amp (AC or DC) 1500 VDC. Special outputs up to 300,000 volts AC or DC and high frequencies are available.
    [Show full text]
  • Design Tips for Linear and Switched‐Mode Power Supplies
    Analog Design Journal Power Design tips for linear and switched-mode power supplies By Billy Long Systems Engineer Introduction the rate of change of flux in that conductor. Energy transmitted through the electric grid is transmit- dΦ VN= (1) ted at very high voltages to reduce the amount of copper dt lost as heat in the wires; however, most electrical and where N is the number of turns of the conductor subject electronic applications use much lower voltages. to the change in flux, Φ. One of the main reasons why the power grid uses AC The magnetic flux in a single-conductor loop = B × A, currents and voltages is that it is relatively easy to use where B is the flux density/unit area and A is the area of transformers to convert AC power from one voltage to the loop. The relationship of induced voltage to induced another. This technology was readily available during the flux density is shown by Equation 2. initial development and deployment of power grids in the (2) late 19th and early 20th centuries. ∫ V× dt = N ×Φ = NB× × A To convert the typical grid voltage of 90 VAC to 240 VAC Because the inductance (and hence impedance) of the (depending on global location) down to a lower voltage, transmission lines used in the AC grid increases with early electronic applications used a linear power supply, frequency, the operating frequency of grids around the shown in Figure 1. world was standardized in the 50- to 60-Hz range. This The line voltage is applied to a transformer, which frequency, in conjunction with the rms grid voltages converts the input voltage down to a lower voltage.
    [Show full text]
  • Switch Mode Power Supplies and Their Magnetics Tutorial
    Datatronic Switch Mode Power Supplies and their Magnetics Many factors must be considered by designers when choosing the magnetic components required in today’s electronic power supplies DATATRONIC DISTRIBUTION, INC. Datatronic In today’s day and age the most often used topology for electronic power supplies is that of the Switch Mode Power Supply (SMPS), which is a major user of magnetics. In some applications the “older type” linear supplies are still used, but in the early 70’s SMPS came into being spurred by the development of faster switching transistors. This facilitated the use of much smaller magnetic components and greater efficiencies. DATATRONIC DISTRIBUTION, INC. Datatronic SMPS and their General Magnetic Usage In general, there are four different types of magnetic components that are needed for the typical SMPS. They include the Output Transformer, usually the most noticeable because of its size compared to the others, the Output Inductors, the Input Inductors and the Current Sense Transformer, each with its own important function. DATATRONIC DISTRIBUTION, INC. Datatronic SMPS and their General Magnetic Usage 1.The Output Transformer or “Main” Transformer takes the input voltage that is supplied to its primary winding and then transforms the input voltage to one or more voltages that are the output of the secondary winding or windings. 2. The Output Inductors are used to filter the output voltage so that the load “sees” a filtered DC voltage. DATATRONIC DISTRIBUTION, INC. Datatronic SMPS and their General Magnetic Usage 3. The Input Inductors filter out the noise generated by the switching transistors so that this noise isn’t emitted back to the source.
    [Show full text]
  • How to Select a Capacitor for Power Supplies
    CAPACITOR FUNDAMENTALS 301 HOW TO SELECT A CAPACITOR FOR POWER SUPPLIES 1 Capacitor Committee Upcoming Events PSMA Capacitor Committee Website, Old Fundamentals Webinars, Training Presentations and much more – https://www.psma.com/technical-forums/capacitor Capacitor Workshop “How to choose and define capacitor usage for various applications, wideband trends, and new technologies” The day before APEC, Saturday March 14 from 7:00AM to 6:00PM Capacitor Industry Session as part of APEC “Capacitors That Stand Up to the Mission Profiles of the Future – eMobility, Broadband” Tuesday March 17, 8:30AM to Noon in New Orleans Capacitor Roadmap Webinar – Timing TBD – Latest in Research and Technology Additional info here. Short Introduction of Today‘s Presenter Eduardo Drehmer Director of Marketing FILM Capacitors Background: • Over 20 years experience with knowledge on +1 732 319 1831 Manufacturing, Quality and Application of Electronic Components. [email protected] • Responsible for Technical Marketing for Film Capacitors www.tdk.com 2018-09-25 StM Short Introduction of Today‘s Presenter Edward Lobo was born in Acushnet, MA in 1943 and graduated from the University of Massachusetts in Amherst in 1967 with a BS in Chemistry. Ed worked for Magnetek, Aerovox and CDE where he is currently Chief Engineer for New Product Development. Ed Lobo Ed has served for over 52 years in Chief Engineer, New Product capacitor product development. He holds [email protected] 14 US patents involving capacitors. 4 ABSTRACT This presentation will guide individuals selecting components for their Electronic Power Supplies. Capacitors come in a wide variety of technologies, and each offers specific benefits that should be considered when designing a Power Supply circuit.
    [Show full text]
  • Aluminum Electrolytic Capacitors Power Application Capabilities
    VISHAY INTERTECHNOLOGY, INC. aluMinuM electrolYtic capacitors Power Application Capabilities Aluminum Electrolytic Capacitors in Power Applications POWER APPLICATIONS • Motor Drives • Solar Inverters • Traction in trains or rolling stock • Uninterruptible Power Supply (UPS) • Pulsed Power RESOURCES • For technical questions contact [email protected] • Sales Contacts: http://www.vishay.com/doc?99914 A WORLD OF SOLUTIONS CAPABILITIES 1/11 VMN-PL0453-1610 THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 www.vishay.com VISHAY INTERTECHNOLOGY, INC. aluMinuM electrolYtic capacitors for Motor Drives Introduction to the Application Motor drives are used to control the speed of various motors in all kinds of systems, from the small pumps and motors in household washing machines and central heating and air-conditioning systems to the large motors found in industrial machinery. Selecting the Best Capacitor for Your Motor Drive Application Aluminum capacitors are often used as DC link capacitors in motor drives, both in 1-phase and 3-phase designs. The aluminum capacitor is used as an energy buffer to ensure stable operation of the switch mode inverter driving the motor. The aluminum capacitor also functions as a filter to prevent high-frequency components from the switch mode inverter from polluting the mains voltage. The key selection criterion for the aluminum capacitor is the required ripple current. The ripple current consists of two components, a low-frequency ripple (50 Hz to 200 Hz) from the input and a high-frequency component from the inverter, typically 8 kHz to 20 kHz.
    [Show full text]
  • AN-500: Depletion-Mode Power Mosfets and Applications
    INTEGRATED CIRCUITS DIVISION Application Note AN-500 Depletion-Mode Power MOSFETs and Applications AN-500-R03 www.ixysic.com 1 INTEGRATED CIRCUITS DIVISION AN-500 1 Introduction Applications like constant current sources, solid state relays, and high voltage DC lines in power systems require N-channel depletion-mode power MOSFETs that operate as normally-on switches when the gate-to-source voltage is zero (VGS=0V). This paper will describe IXYS IC Division’s latest N-channel, depletion-mode, power MOSFETs and their application advantages to help designers to select these devices in many industrial applications. Figure 1 N-Channel Depletion-Mode MOSFET D ID + G V + DS IG V - GS I - S S A circuit symbol for an N-channel depletion-mode power MOSFET is given in Figure 1. The terminals are labeled as G (gate), S (source) and D (drain). IXYS IC Division depletion-mode power MOSFETs are built with a structure called vertical double-diffused MOSFET, or DMOSFET, and have better performance characteristics when compared to other depletion-mode power MOSFETs on the market such as high VDSX, high current, and high forward biased safe operating area (FBSOA). Figure 2 shows a typical drain current characteristic, ID, versus the drain-to-source voltage, VDS, which is called the output characteristic. It’s a similar plot to that of an N-channel enhancement mode power MOSFET except that it has current lines at VGS equal to -2V, -1.5V, -1V, and 0V. Figure 2 CPC3710 - MOSFET Output Characteristics Output Characteristics (TA=25ºC) 300 270 VGS=0.0V 240 210 V =-1.0V 180 GS 150 (mA) D I 120 V =-1.5V 90 GS 60 V =-2.0V 30 GS 0 0123456 VDS (V) The on-state drain current, IDSS, a parameter defined in the datasheet, is the current that flows between the drain and the source at a particular drain-to-source voltage (VDS), when the gate-to-source voltage (VGS) is zero (or short-circuited).
    [Show full text]
  • Differences Between Power Supplies, Inverters, and Transformers
    Differences Between Power Supplies, Inverters, and Transformers [0m:0s] [0m:4s] Hi I'm Josh Bloom, welcome to another video in the RSP Supply education series. In today's video we're going to be looking at some of the differences between several pieces of hardware that often get confused, even though they are intended for very different purposes. This hardware includes power supplies, [0m:23s] transformers, inverters, and voltage converters. [0m:28s] All of this hardware is intended to alter or change the type of power or voltage that you might be using. [0m:35s] The result you need will directly impact which type of hardware you may want to choose. [0m:41s] However, it is very common for people to confuse the different types of hardware. Let's discuss each type and what it is intended to do so hopefully by the end of the video you'll be able to have a very clear understanding of each and when you might want to use them. Let's first start with power supplies. A power supply can have many different functions, RSPSupply www.rspsupply.com 1-888-532-2706 www.youtube.com/RSPSupply [1m:2s] but most of the time the power supply is intended to take one type of power and convert it to another type of power. The most common example of this is a power supply that takes AC power and converts it to DC power. [1m:17s] While it is very common to use power supplies and industrial applications, one very common place you will see a power supply being used is for the gadgets you have around your home, such as your smartphone or laptop or tablet, RSPSupply www.rspsupply.com 1-888-532-2706 www.youtube.com/RSPSupply [1m:31s] or many other devices we use on a daily basis.
    [Show full text]
  • Ten Fundamentals You Need to Know About Your DC Power Supply
    Keysight Technologies Ten Fundamentals You Need to Know About Your DC Power Supply Application Note Introduction Understanding how measurement tools operate can provide insight into how to improve testing methods. With modern performance and safety features in power supplies, the lexibility exists to create test setups that are simpler and more effective. Use these 10 fundamentals about your power supply to take advantage of these features. Contents 1 Program Your Power Supply Correctly to Operate in Constant Voltage or Constant Current Mode / 3 2 Use Remote Sense to Regulate Voltage at Your Load / 4 3 Use Your Power Supply to Measure DUT Current / 5 4 Connect Power Supply Outputs in Series or Parallel for More Power / 6 5 Minimize Noise From Your Power Supply to Your DUT / 7 6 Safeguard Your DUT Using Built-in Power Supply Protection Features / 8 7 Use Output Relays to Physically Disconnect Your DUT / 9 8 Capture Dynamic Waveforms Using a Power Supply’s Built-in Digitizer / 10 9 Create Time-Varying Voltages Using Power Supply List Mode / 11 10 Tips for Rack-Mounting Your Power Supply / 12 Glossary / 13 Resources / 14 2 DC Power Supply Fundamentals Program your Power Supply Correctly to Operate 1 in Constant Voltage or Constant Current Mode The output of a power supply can operate current limit setting. This operating mode Possible causes of UNR include: in either constant voltage (CV) mode or is known as constant current (CC). In –The power supply has an constant current (CC) mode depending on Figure 1, the power supply will operate on internal fault.
    [Show full text]
  • MOSFET Gate Drive Circuit Application Note
    MOSFET Gate Drive Circuit Application Note MOSFET Gate Drive Circuit Description This document describes gate drive circuits for power MOSFETs. © 2017 - 2018 1 2018-07-26 Toshiba Electronic Devices & Storage Corporation MOSFET Gate Drive Circuit Application Note Table of Contents Description ............................................................................................................................................ 1 Table of Contents ................................................................................................................................. 2 1. Driving a MOSFET ........................................................................................................................... 3 1.1. Gate drive vs. base drive.................................................................................................................... 3 1.2. MOSFET characteristics ...................................................................................................................... 3 1.2.1. Gate charge ........................................................................................................................................... 4 1.2.2. Calculating MOSFET gate charge ....................................................................................................... 4 1.2.3. Gate charging mechanism ................................................................................................................... 5 1.3. Gate drive power ................................................................................................................................
    [Show full text]
  • EXP4: Rectifiers
    EXP4: Rectifiers OBJECTIVES. The general objective of this experiment is for you to become familiar with the response of a diode in a circuit, whether the circuit is supplied with a DC, AC or AC-DC voltage. In this part we will also see how to couple AC and DC sources, and finally we will illustrate the use of diodes in rectifying circuits. INTRODUCTION AND TEST CIRCUITS. The circuits we will be studying are the basic limiting circuit, half-wave and full-wave rectifiers. We will be doing the analysis of the circuits using aproximation, such as assuming we know the diodes’ voltage Vf . Also we will make use of the graphical method to find the voltage and current in the diode. We will run a bias analysis using PSpice which is the same as using an iterative method. And finally we will measure in lab the actual voltage and current values. That way we will be able to evaluate the accuracy of the different methods. We will also get the transfer characteristic, and use it to predict the output waveform for a given input. We will check our estimate using PSpice and in lab. For theory on the behavior of the circuits we will be studying please refer to the textbook or some book that covers the topics, limiting and rectifying circuits. PREPARATION. For the first two circuits, the limiting and the half-wave rectifier we will do the analysis using different methods. If you are not familiar with any of these methods please refer to the textbook or some book that covers this topic.
    [Show full text]