DOCSLIB.ORG

Introduction to Led Power Sources

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Introduction to Led Power Sources INTRODUCTION TO LED POWER SOURCES BY JEFF CIARLETTE • MOLEX INC active. The forward current requirements are usually 10mA to 20mA. There is little INTRODUCTION requirement for a precise amount of current for these types application, since there is usually Properly powering a light emitting diode (LED) or only one LED used for indication and slight group of LEDs is different than powering most variations in luminous intensity from one electronics. While most electronics require a indicator to a nearby indicator are not important constant voltage source, LEDs require a as long as each indicator is visible and relatively constant current source. Most power supplies of the same brightness. will provide a set voltage, such as 5V, and have a maximum current rating. The power supply The power required to power LEDs used for will maintain this voltage and provide enough lighting is much greater than that used for current to meet the demand of the circuit it is indicator LEDs. As a result, efficiency becomes powering. This means a dedicated power a concern. Some methods of powering LEDs supply would need to be implemented to drive are very inefficient and result in large power any LEDs in a circuit. losses. These losses are usually counterproductive, as LEDs are often chosen to For an LED to properly operate, the power increase efficiency of lighting systems over other supply must have a high enough voltage to turn methods, such as incandescent lighting. LEDs on (illuminate) the LED and it must provide a in these applications may require hundreds of controlled constant amount of current to the milliamps to generate the light output they’re LED. The voltage required to illuminate the LED capable of producing. A typical If for these types is called the forward voltage (Vf). The amount of of LEDs is around 350mA. current the LED uses when illuminated is called the forward current (If). Forward current is Since these applications involve multiple LEDs typically specified as a maximum value. Current used to illuminate an area, sign, screen, etc, the above this rating can damage the LED. LED light output needs to be controlled. The light light output varies with the forward current. output is measured either in Lumens or Decreasing the forward current decreases the Candelas. The unit Candela is the power of a LED light output. light source emitted in a particular direction. The unit Lumen is the amount of light from one Candela of a solid angle of one steradian. These applications typically specify high luminous intensity. Therefore, the power supply used must be efficient, and control the output current with precision. Figure 1: LED Showing Forward Voltage and Current In this discussion, we will divide LEDs into two categories – indicator LEDS and LEDs used for lighting. Indicator LEDs are very low power and are used to illuminate a small indicator. An example of an indicator LED is the LED on a PC Figure 2: High Power LED Lamp or laptop that illuminates when the hard drive is Page 1 of 4 INTRODUCTION TO LED POWER SOURCES LED POWER SOURCES Rather than use a current limiting resistor with a constant voltage source, a better solution is to The simplest way to power an LED is to use a design a constant current power supply. While DC constant voltage source that is already there are very simple linear constant current powering other electronics in the circuit. Current supplies available, a switching mode power can be controlled with a series resistor. See supply (SMPS) is more efficient. This is Figure 3. This is inexpensive and convenient, because a linear supply dissipates all the power especially if power is already being supplied to lost for the voltage conversion. So if a linear other components. regulator is being used to convert 12V to 3.5V and the load is 350mA, the total power consumed is: Ptot = (12V)(0.350A) = 4.2W The power used by the LED is: PLED = (3.5V)(0.35A) = 1.23W The power dissipated in the regulator is: Figure 3: Simple LED Circuit with Current PLINEAR = Ptot – PLED = 2.98W Limit Resistor However, most SMPS’s are around 90% This is a common way to power indicator LEDs. efficient. For the above example, the power For lighting applications, it has some drawbacks. consumed would be: One drawback is that it is inefficient. All the power dropped across the resistor is lost as Ptot = (Vout)(Iout)/90% heat. For example, using a 5V source to power Ptot = (3.5V)(0.35A)/(0.90) = 1.36W an LED with a Vf of 3.5V and an If of 350mA results in a 1.5V drop over the resistor. PLED = (3.5V)(0.35) = 1.23W (1) P = VI PSMPS = Ptot – PLED = 0.13W P = (1.5V)(0.35A) = 0.525W This equates to 0.13W lost in the power conversion using a switching regulator versus That is a total of 525mW wasted just to power 2.98W in a linear regulator. one LED. Switching power supply controllers designs are Another drawback is the inability to closely more complex than a linear regulator design and control the current. Since V can vary from f usually consist of the following components: LED to LED, the voltage drop across the resistor can vary. Therefore, the current can vary from 1. Controller IC one LED to another. If the current varies, the 2. High Side MOSFET light output varies. 3. Catch Diode or Low Side MOSFET 4. Inductor When multiple LEDs are being powered, both of 5. Resistors and Capacitors for feedback, these drawbacks become even more apparent. compensation, and other filtering In the case of the 5V supply, the LEDs would need to be powered in parallel. So there would Depending on the type of SMPS, either a catch be power lost across multiple resistors and the diode or a low side MOSFET will be used. light output could vary from one LED to another. Page 2 of 4 INTRODUCTION TO LED POWER SOURCES Some controllers integrate the high side Another disadvantage is the physical size the MOSFET. Depending on the number and type switcher circuit may require. Most of the of LEDs being powered, a potential downside to components in a switcher circuit, including the having a controller with an integrated MOSFET controller are relatively small. However, is the MOSFET is housed in the same package depending on the current requirements and as the controller and usually allows for less switching frequency, the inductor can be quite power dissipation than can be achieved with a large. An SMPS circuit with its external MOSFET in an external power package. components can easily require a square inch of Therefore, the total output current is lower than board space. In most high power LED cases, what can be achieved with an external power the advantages far outweigh the loss of MOSFET. efficiency in using other methods. SERIES OR PARALLEL In applications consisting of multiple LEDs, another consideration is whether to power the LEDs in series or in parallel. Since the supply voltage available is often too low to overcome Vf of more than one LED, it may seem like powering the LEDs in parallel would be the preferred method. However, there are a few disadvantages to powering an LED in parallel. These include: 1. Light output can vary from one LED to another. 2. If an LED fails open, the other LEDs could Figure 4: Example of Constant Current SMPS be damaged. Another advantage of using a switching power 3. The amount of current required from the supply is the ability to boost the output voltage. power supply increases with each LED. Boost converters have the capability of providing First, V can vary from LED to LED. Therefore I a greater output voltage than input voltage. This f f will vary, which causes the light output to vary. is advantageous for LEDs as it allows more Also, LEDs have a negative temperature LEDs to be placed in series. It also allows for coefficient. This means the hotter it gets, the the use of portable batteries as their supply lower the resistance or the more current it voltage may be less than Vf of a single LED. draws. Drawing more current makes the LED There are some disadvantages to using a even hotter. Note that light output can vary from switching power supply. Since they are LED to LED all things being equal due to switching, they have the potential to cause manufacturing variances between LEDs. problems with radiated emissions. Proper layout However binning, or grouping the LEDs by light of the power supply is critical to reduce current output characteristics, is done by LED loop size, crosstalk noise, and thermal issues. A manufacturers. The light output variation may large current loop can act like an antenna. be subtle. Depending on the application, any Depending on other factors, such as size and noticeable variation may or may not be tolerable. shape of the area used to layout the switcher, a Another problem is if an LED fails “open”, more layout that minimizes EMI can often be very current will go to the others. This can potentially difficult to realize. Strict layout rules must be burn out the other LEDs. In the case of a short, enforced. Page 3 of 4 INTRODUCTION TO LED POWER SOURCES there is too little current to the other LEDs. To SUMMARY operate under these conditions additional circuitry would be needed to monitors faults and LED assemblies often require high power and adjust the current available to the other LEDs. attention to the quality of light output.
Load more

Recommended publications
  • Phys 586 Laboratory Lab11
    Phys 586 Laboratory Lab11 Goal: In this lab you will make measurements with a photodiode. While not the same type of diode used in diode arrays for radiation planning or microstrip detectors in high energy physics, many of the basic device characteristics are the same. Additionally, photodiodes are used in x-ray imaging (along with a scintillator layer) and avalanche photodiodes find application in high energy physics. Reading: See Photodiode Characteristics article in the Readings. Lab: 1. Construct the LED circuit shown in Figure 1. a) Is the LED forward or reverse biased? The LED is forward biased. b) What is the purpose of the resistor? The value of the resistor is chosen so that the specified LED operating current results in the desired LED voltage drop. The value that this resistor should have can be determined using Kirchhoff’s loop rule and Ohm’s Law. Vary the voltage and convince yourself the brightness of the LED changes. Note the longer leg on the LED is the anode. 1 2. Measure the current through the LED and the voltage across the LED for LED supply voltages of 2.5, 5, 8, 10, 13, 15, 18 and 20V. LED LED LED Supply Voltage Current Voltage (V) (V) (mA) 2.5 1.67 2.46 5.01 1.76 4.91 8.01 1.82 7.8 10.05 1.85 9.9 13 1.9 12.83 15 1.92 14.9 18 1.96 17.82 20 1.99 20.1 Circuit 1: LED Current vs LED Voltage 25 20 15 10 LED Current (mA) 5 0 1.65 1.7 1.75 1.8 1.85 1.9 1.95 2 2.05 LED Voltage (V) 2 3.
    [Show full text]
  • Photodiode and LIGHT EMITTING DIODE
    Photodiode and LIGHT EMITTING DIODE Presentation by JASWANT KUMAR ROLL NO.-12 rd IT(3 SEM.) 1 About LEDs (1/2) • A light emitting diode (LED) is essentially a PN junction opto- semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction. • LEDs convert electrical energy into light energy. LED SYMBOL 2 ABOUT LEDS (2/2) • The most important part of a light emitting diode (LED) is the semi-conductor chip located in the center of the bulb as shown at the right. • The chip has two regions separated by a junction. • The junction acts as a barrier to the flow of electrons between the p and the n regions. 3 LED CIRCUIT • In electronics, the basic LED circuit is an electric power circuit used to power a light-emitting diode or LED. The simplest such circuit consists of a voltage source and two components connect in series: a current-limiting resistor (sometimes called the ballast resistor), and an LED. Optionally, a switch may be introduced to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester. 4 HOW DOES A LED WORK? • Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. • For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi- conductor material. 5 Mechanism behind photon emission in LEDs? MechanismMechanism isis “injection“injection Electroluminescence”.Electroluminescence”.
    [Show full text]
  • LED Circuit and Device Physics 120 Pts Objective: Meas
    Applied Quantum Mechanics for Electrical Engineers Workshop III – LED Circuit and Device Physics 120 pts Objective: Measure the voltage drop across an LED in a simple circuit, demonstrate that the voltage drop is proportional to the band gap of the semiconductor material, and analyze the behavior of the circuit in terms of the device physics of the PN junction. Background: A light emitting diode (LED) is a device that is designed by fabricating a PN junction or diode as illustrated in Figure 1. Figure 1. Schematic of LED and illustration of carrier movement resulting in emission of light. Image: http://blog.ucsusa.org/wp-content/uploads/2014/10/UCS-LED-how-it-works-graphic.gif A simple PN junction can be fabricated by growing a p-type material on top of an n-type material, or by doping an n-type material with sufficient p-type dopants so that the surface becomes p-type. The energy band diagram for a PN Junction under forward bias conditions is illustrated in Figure 2, along with a schematic of the circuit under forward bias. Figure 2. LED circuit and PN Junction energy band diagram illustrating carrier movement under forward bias. Image: http://www.vit.ac.in/onlinelab/m9.aspx The application of a forward bias to the circuit results in a decrease in the barrier to electron movement from the n-side to the p-side. Likewise, the barrier of hole movement from the p- side to the n-side is also reduced. Thus, majority carriers from each side are able to cross the energy barrier.
    [Show full text]
  • LUXEON Illumination Leds Circuit Design and Layout Practices to Minimize Electrical Stress
    ILLUMINATION LUXEON Illumination LEDs Circuit Design and Layout Practices to Minimize Electrical Stress Introduction LED circuits operating in the real world can be subjected to various abnormal electrical overstress situations. Among the most common are: • Isolation test during validation or production of the luminaire (“hi-pot test”) • Lightning strikes and line transients • Hot-swapping of LED circuits (disconnecting and reconnecting an LED circuit board to the driver while the driver remains powered up) • Driver failures • ESD (Electro-Static Discharge) Scope This paper presents background information on some of these overstress modes and discusses recommendations to minimize the potentially destructive effects of electrical overstress on LEDs. AB06 LUXEON LEDs Application Brief ©2016 Lumileds Holding B.V. All rights reserved. Table of Contents Scope . 1 1 . Electrical Overstress . 3 2 . Isolation Test Requirements . 3 3 . Isolation Test on an LED Board . 4 4 . LUXEON Rebel LED Circuit Model on a Board . 5 5 . Electrical Stress Simulation during Isolation Test . 6 6 . Protection Circuits . 8 7 . High Voltage Drivers . 10 8 . Lightning Strikes and Line Transients . 11 9 . Recommendations . 11 About Lumileds . 12 AB06 LUXEON LEDs Application Brief 20170605 ©2017 Lumileds Holding B.V. All rights reserved. 2 1. Electrical Overstress Electrical Overstress (EOS) can present itself to an LED array in two forms, either as excess voltage or excess current. Because voltage and current are interrelated, it is not always possible to identify whether a high voltage or high current caused a failure. Currents can flow through an LED array in two ways: differential mode and common mode (see Figure 1). Differential mode currents can be very destructive.
    [Show full text]
  • The Importance of Leds in Switches
    WHITEPAPER The Importance of LEDs in Switches LEDS PROVIDE ADDITIONAL OPTIONS FOR DESIGNERS AND IMPROVE THE FUNCTIONALITY OF THE SWITCH NKK SWITCHES THE IMPORTANCE OF LEDs IN SWITCHES Why put an LED on a switch? LEDs are a simple, compact way to indicate the status of a circuit. By having the LED in the switch, it reduces space and component count for an assembly. There are many ways to control LEDs. Some indicator circuits use the switch’s own circuity in an ON-OFF fashion. Others are bicolor or even RGB and are hooked up to a microprocessor to give additional visual feedback. Most of the illuminated switches available at NKK Switches have the LED circuit separate from that of the switching circuit. This is to provide maximum flexibility for design. 1. The two circuits found in an illuminated switch (single pole) Switching Circuit LED Circuit UB2 1 L (+) L(+) NC NC R1 +VDC Switching NO NO LED Circuit Circuit 3 2 GND L(-) L (-) COM COM The simple indicator circuit shown above is one that uses a spare pole on the switch to turn OFF and ON the LED to show that a circuit is connected. This type of circuit just shows the state of the switch, either OFF or ON, with the reasonable assumption that if the LED is illuminated then the load circuit is active as well. 2. Simple single LED ON-OFF indicator using the second pole of a double pole switch to light the LED. The dotted line indicates that the two poles are mechanically connected to each other.
    [Show full text]
  • Circuit Topology Analysis for LED Lighting and Its Formulation Development
    energies Article Circuit Topology Analysis for LED Lighting and its Formulation Development William Chen, Ka Wai Eric Cheng * and Jianwei Shao Power Electronics Research Centre, Department of Electrical Engineering, The Hong Kong Polytechnic University, Kowloon 999077, Hong Kong, China; [email protected] (W.C.); [email protected] (J.S.) * Correspondence: [email protected] Received: 30 July 2019; Accepted: 24 October 2019; Published: 4 November 2019 Abstract: Light emitted diode (LED) is becoming more popular in the illumination field, and the design of LED lighting is generally made to provide illumination at lower power usage, helping save energy. A power electronic converter is needed to provide the power conversion for these LEDs to meet high efficiency, reduce components, and have low voltage ripple magnitude. The power supply for LED is revisited in this paper. The LEDs connected in series with diode, transistor, or inductor paths are examined. The formulation for each of the cases is described, including the classical converters of buck, boost, buck–boost, and Cuk.´ The circuit reductions of the classic circuit, circuit without the capacitor, and without a freewheeling diode are studied. Using LED to replace freewheeling diodes is proposed for circuit component reduction. General equations for different connection paths have been developed. The efficiency and output ripple amplitude of the proposed power converters are investigated. Analytical study shows that the efficiency of proposed circuits can be high and voltage ripple magnitude of proposed circuits can be low. The results show that the proposed circuit topologies can be easily adapted to design LED lighting, which can meet the criteria of high efficiency, minimum components, and low-voltage ripple magnitude at the same time.
    [Show full text]
  • Integration of Photodiode As a Data Receiver in Visible Light Communication Circuit
    International Journal of Scientific Engineering and Science Volume 4, Issue 9, pp. 67-77, 2020. ISSN (Online): 2456-7361 Integration of Photodiode as a Data Receiver in Visible Light Communication Circuit ANUSIUBA Overcomer Ifeanyi Alex1, EKWEALOR Oluchuku Uzoamaka2, ORJI Ifeoma Maryann3, AKAWUKU Godspower I4 1, 2, 3, 4Department of Computer Science, Faculty of Physical Sciences, Nnamdi Azikiwe University Awka Anambra State Nigeria E-mail: [email protected], [email protected], [email protected], [email protected] Abstract— The exponential increase of mobile data traffic in the last two decades has identified the limitations and deficiency of RF-only mobile communications. Visible light communication VLC research has shown that it is capable of achieving very high data rates (nearly 100 Mbps in IEEE 802.15.7 standard and up to multiple Gbps) however lacking practical implementation. Several modulation techniques have been proposed in theory to improve the data rate and maximum range of VLC system. In practice, the intensity modulation tends to be susceptible to ambient noise while pulse width modulation flickers the LED at a human eye disturbing frequency. Based on the limitations of the past attempts to practically implement a noiseless transmission at a high data rate, this work focused on designing, implementing and integration of photodiode as a data receiver for a real time VLC system capable of noiseless data transmission using quasi pulse with modulation. The design adopted Beagle-Bone-Black (BBB) as development platform while prototype modeling methodology was adopted for VLC implementation and the circuit was tested with PROTUES 8 Professional and data sent reliably and accurately over a short distance at a fair speed which ensures that the initial goals for the functionality of this new system which includes being able to send audio, text or pictures over a distance of approximately 10 meter at a data rate of at least 10 Mbps was achieved using Photodiode as Data Receiver.
    [Show full text]
  • All About LED's (PDF)
    All About LEDs Created by Tyler Cooper Last updated on 2018-08-22 03:33:51 PM UTC Guide Contents Guide Contents 2 Overview 4 What is an LED? 5 All the different sizes and colors 6 What are LEDs used for? 9 Changing the brightness with resistors 12 Which LED is brightest (what is the resistor)? 13 Which LED is dimmest (what is the resistor)? 13 If we had an LED with a resistor that was 5K ohms, which LED would it be brighter than? Which LED would it be dimmer than? 13 Changing the brightness with voltage 13 Which LED is brightest (what is the voltage)? 14 Which LED is dimmest (what is the voltage)? 14 If we had an LED with a 1.0K resistor connected to a 4.2v supply, which LED would it be brighter than? Which LED would it be dimmer than? 14 Max brightness!? 14 We connect our LED to the resistor, as we turn it from infinite to to zero, what happens? 14 We connect our LED through a 1K resistor, as we adjust the voltage from 0 volts to infinite volts, what happens? What happened? 1515 The LED datasheet 16 Forward Voltage and KVL 18 Quick Quiz! 19 Let's say we have the same circuit above, except this time its a 5V battery and an LED with a forward voltage of 2.5V, how much voltage must be 'absorbed' by the resistor? 19 Let's say we have the same circuit above, except this time its a 5V battery and an LED with a forward voltage of 3.4V, how much voltage must be 'absorbed' by the resistor? 19 Ohm's Law 19 If I have a 3 ohm resistor (R) with a current of 0.5 Amperes (I) going through it.
    [Show full text]
  • Pre-College Engineering Activities with Electronic Circuits (Work in Progress)
    Paper ID #14965 Pre-College Engineering Activities with Electronic Circuits (Work in Progress) Dr. Jacquelyn Kay Nagel, James Madison University Dr. Jacquelyn K. Nagel is an Assistant Professor in the Department of Engineering at James Madison Uni- versity. She has eight years of diversified engineering design experience, both in academia and industry, and has experienced engineering design in a range of contexts, including product design, bio-inspired de- sign, electrical and control system design, manufacturing system design, and design for the factory floor. Dr. Nagel earned her Ph.D. in mechanical engineering from Oregon State University and her M.S. and B.S. in manufacturing engineering and electrical engineering, respectively, from the Missouri University of Science and Technology. Dr. Nagel’s long-term goal is to drive engineering innovation by applying her multidisciplinary engineering expertise to instrumentation and manufacturing challenges. Dr. Steve E. Watkins, Missouri University of Science & Technology Dr. Steve E. Watkins is Professor of Electrical and Computer Engineering at Missouri University of Science and Technology, formerly the University of Missouri-Rolla. His interests include educational innovation. He is active in IEEE, HKN, SPIE, and ASEE including service as the 2015-17 Zone III Chair. His Ph.D. is from the University of Texas at Austin (1989). c American Society for Engineering Education, 2016 Work in Progress – Pre-college Engineering Activities with Electronic Circuits Abstract Projects involving engineering experimentation, design, and measurement can be effective content for pre-college STEM outreach. Such applications-oriented activities can promote literacy and interest in technical topics and careers and have the added benefit of showing the relevance of science and mathematics.
    [Show full text]
  • Required Tools and Components
    APPENDIX A Required Tools and Components This appendix includes the most common components and tools you will need for each of the projects in the book. There are suggested design alternatives for some of the projects so you may want to explore other components. I also list suggested sizes or types for some of the tools, which should be considered only as a guide. It’s often a good idea to start with a small set of basic tools and then expand that collection or add better-quality tools as you gain more experience. I’ve listed the tools in a few groups, which will allow you to add to your tools as you progress. I’ve listed the components for each of the projects, some of which may have already been used by other projects. Tools Required When getting started then only a few basic tools are required. This includes a breadboard to build the circuits on and a pair of side cutters to cut and strip wires. When making permanent circuits then the number of tools required does increase, although some of these are normal DIY tools that you may already have or that you may find useful around the home. Basic Breadboard Circuits These are the recommended tools in Chapters 1 to 7 (and later): • Raspberry Pi (preferably Raspberry Pi 2) • Breadboard (half size) • Side cutters (small wire cutters) • Crocodile clips with wires • Jumper wires and/or solid core wire • Small screwdriver (cross-head and straight, or multi-head) • Cobbler (optional) • Board to mount the Raspberry Pi and breadboard (optional) Crimping and Soldering Tools A crimping tool is useful in Chapter 3 ; the rest of the tools are used in Chapters 10 and 11 .
    [Show full text]
  • 50 Simple L.E.D. Circuits
    50 Simple L.E.D. Circuits R.N. SOAR r de Historie v/d Radi OTH'IEK 50 SIMPLE L.E.D. CIRCUITS by R. N. SOAR BABANI PRESS The Publishing Division of Babani Trading and Finance Co. Ltd. The Grampians Shepherds Bush Road London W6 7NI- England Although every care is taken with the preparation of this book, the publishers or author will not be responsible in any way for any errors that might occur. © 1977 BA BAN I PRESS I.S.B.N. 0 85934 043 4 First Published December 1977 Printed and Manufactured in Great Britain by C. Nicholls & Co. Ltd. f t* -i. • v /“ ..... tr> CONTENTS U.V.H.R* Circuit Page No. 1 LED Pilot Light......................................... 7 2 LED Stereo Beacon.................................... 8 3 Stereo Decoder Mono/Sterco Indicator . 9 4 Subminiature LED Torch........................... 10 5 Low Voltage Low Current Supply............ 11 6 Microlight Indicator .................................. 12 7 Ultra Low Current LED Switching Indicator 13 8 LED Stroboscope....................................... 14 9 12 Volt Car Circuit Tester........................... 15 10 Two Colour LED......................................... 16 11 12 Volt Car “Fuse Blown” Indicator.......... 17 12 LED Continuity Tester............................... 17 13 LED Current Overload Indicator.............. 18 14 LED Current Range Indicator................... 20 15 1.5 Volt LED “Zener”................. '............ 22 16 Extending Zener Voltage........................... 22 17 Four Voltage Regulated Supply................. 23 18 PsychaLEDic Display.................................. 24 .19 Dual Colour Display.................................... 25 20 Dual Signal Device....................................... 26 21 LED Triple Signalling.................................. 27 22 Sub-Miniature Light Source for Model Railways . 28 23 Portable Television Protection Circuit . 29 24 Improved Portable TV Protection Circuit 30 25 LED Battery Tester..............................
    [Show full text]
  • Fundamentals to Automotive LED Driver Circuits
    Fundamentals to automotive LED driver circuits Kathrina Macalanda Product Marketing Engineer Power Switches, Interface & Lighting Texas Instruments LED circuits: simple to turn on, complex to design. LEDs are current-driven devices that are substantially affected by changes in operating conditions, such as voltage and temperature. LEDs used in the automotive environment are subject to a wide range of operating conditions, and LEDs can commonly degrade or permanently fail before their expected lifetime. A proper circuit design can enhance LED longevity and performance. In a car, LEDs are a popular choice for illumination that meets current accuracy, board size, thermal from tail-lights in the rear to telltale status indicators management and fault detection requirements in the cluster as shown in Figure 1. Their small size across operating temperature range and input enables flexibility in styling and has the potential to voltage conditions. last as long as the vehicle’s lifespan. However, LEDs In addition, as the number of LEDs grows or project are susceptible to damage from unstable voltage, requirements become more complex, circuit design current and temperature conditions, especially in the with discrete transistors becomes more complex. rugged automotive environment. To optimize their In contrast to designing with discrete components, efficiency and longevity, LED driver circuit design using integrated solutions can simplify not only requires careful analysis. the circuit design, but also the design and test process. Additionally, the overall solution may be even cheaper. Thus, when designing circuits to drive LEDs in an automotive lighting application, it is important to consider LED priorities, compare circuit design options, and factor in system needs.
    [Show full text]