The authors, noted authorities in the field, offer a review of the most relevant topics including optical performance, materials, thermal design and modeling and measurement. Comprehensive in scope, the text covers all the information needed to design LEDs into end products. The user-friendly text also contains numerous drawings and schematics that show how things such as measurements are actually made, and show how circuits actually work. This thoroughly expanded second edition offers: New chapters on the design of an LED flashlight, USB light, automotive taillight, and LED light bulbs A practical and user-friendly guide with dozens of new illustrations The nitty-gritty, day-to-day engineering and systems used to design and build complete LED systems An essential resource on the cutting-edge technology of Light-Emitting Diodes Practical Lighting Design with LEDs helps engineers and managers meet the demand for the surge in usage for products using light-emitting diodes with a practical guide that takes them through the relevant fields of light, electronic and thermal design.
|Published (Last):||22 January 2010|
|PDF File Size:||10.4 Mb|
|ePub File Size:||7.40 Mb|
|Price:||Free* [*Free Regsitration Required]|
A better choice is to get the converter feedback at the output of the additional filter. This introduces two extra poles, making the converter unstabilizable if the poles are too low in frequency.
Practical Note A good choice is to make the resonant frequency of the additional filter approximately 10 times higher than the bandwidth of the converter. This then gives little phase shift for the compensation to deal with see Chapter 6 , and may still give adequate attenuation at the switching frequency. Generally, the inductance should be made small and the capacitance large, to decrease the converters output impedance.
Practical Note You usually end up with quite small inductance required for this type of post-filtering, perhaps some hundreds of nanohenrys to a few microhenrys. Instead of trying to use a ferrite bead, which has trouble supporting DC current, try using one of the small MPP toroids as a bead, making it a single turn by just passing the output bus through it. The worst load will occur when you need fast transient response and low noise together; then you will have to combine techniques from both these sections, and can expect to spend a lot of sweat on it.
Batteries, Again Batteries were unpleasant sources, so, just as you would expect, they are unpleasant loads, too. The first thing about them is pretty obvious: when you need to charge a battery you cant just apply a voltage to it, because the amount of current the battery takes is exponential in the voltage. You need to have a way of controlling the current. Loads 11 The way charging current is measured in databooks discharge current is measured this way, too is in terms of C.
Notice that C is a current, measured in amps; the capacity of the battery is measured in amp-hours, making its units charge. To get a battery hlly recharged, dont ever discharge a primary battery to zero, it damages the battery , you need to first recharge it at a relatively high rate.
How high? The higher the charge rate, the more inefficient the recharging will be, because the battery will actually warm up. You usually dont want to continue charging at the high rate for this last portion of charge because this can cause the battery to heat. Keeping up the high charge also makes it difficult to know the actual state of the battery, since the resistance of the battery means that the terminal voltage will be higher when a lot of current is being pumped in. Some types of battery can be severely damaged by being overcharged.
Actually, the battery self-discharges, so you have to keep on putting a little bit of current in forever, even when you dont use the battery. This last state, called trickle charge or float charge , is usually done with a voltage rather than a current, because the amount of current required can be so small as to be hard to measure. A typical float-charge regime for a 12V, sealed lead-acid battery might be This application cries out for a microcontroller in your converter.
Are you ready for this? Telephones Telephones, which have been around for years, were designed with large pieces of steel and copper in mind, not semiconductors. They are powered by the phone line, not by the local mains, which is why your phone continues working when the lights go out.
They are thus typically located hundreds of meters away from their power supply, which introduces substantial resistance and inductance between the supply and the phone. A telephone can be modeled as having three different states: either it is not in use, or it is ringing, or else it is off-hook and in use. These three states have different characteristics, and the characteristics of each are naturally different in each country.
To appreciate how hard it is to drive a telephone in the ringing state, consider some sample numbers. In the ringing state, a phone looks like a resistor in series with a capacitance, and it has to be driven by a low frequency sine wave. This sine wave has to have a minimum voltage at the phone of 40V,, in the U. German phones look like 3. Phones in France are required to be more than 2kR and less than 2.
Electronic phones can be almost any load whatsoever, from 6w2 to 60w2 or more! And yet the power supply has no way of knowing which of these telephones it will be powering, unless it is tailored for each country individually; indeed a supply running five phones needs to be able to power both conventional and electronic types simultaneously.
Thus the power supply has to be able to produce this high voltage sine wave into a load that may have either 0 or 90 of phase shift. When you add in cabling inductance, it turns out the load could even be inductive and have a phase! As if this werent nasty enough, when you are talking on the phone, it looks like a pure R resistance. So here you are driving a V,, sine wave into a reactive load, and when the user picks it up, suddenly it becomes a resistor!
Of course, the supply must quickly change its drive-therwise it would be supplying huge power a single supply should be able to power five phones. But because of the differences in phones of different types, the same measurement technique cant be used even to determine when the phone has been picked up. In the United States, for example, they look for a certain level of current since it is mostly resistive , but in Germany, with the big capacitor, there is no substantial change in current although there is in power , so they look for a phase change.
FI uorescen t Tubes Fluorescent tubes are another unusual type of load, driven by a special type of power supply called a ballast. Tubes come in quite a variety of types, the ubiquitous 4-foot-long ones you never pay attention to overhead, 8-foot-long ones you see in supermarkets, circular ones, cold-cathode types you use on your desk, sodium lamps in parking lots, etc.
They all have different characteristics to contend with, but the fundamental distinction among them is whether or not they have heated filaments. Those that dont have heated filaments require only a single pair of wires; those that do work basically the same, but require in addition extra pairs of wires for the filaments.
Since the two types are otherwise similar, this section concentrates on tubes with heated filaments. A fluorescent tube can be thought of as similar to a vacuum tube, except its not a very good vacuum. The glass tube has some gases in it such as argon , and a drop of mercury liquid, which vaporizes when the tube is working.
The glass in turn has some phosphors coating its inside similar to a television tube. The tube works when a voltage is applied across the gas from one end to the other. There is actually a cathode and an anode, but since fluorescent tubes are usually operated with AC, this is an unimportant distinction. AC is used rather than DC so that both ends have a chance to be the anode, reducing wear on the electrode.
The voltage is enough to cause the gas to ionize, which is to say, it forms a plasma. Getting a headache yet? The plasma gives off UV light, which the phosphor coating on the glass changes into visible light. Altogether, this is not a real efficient electrical process, but it is substantially more efficient than what normal incandescent bulbs do, which is to make a piece of metal so hot that it glows.
Leave them intact to be handled by those who know where to dispose of them without contaminating either people or the environment. When a fluorescent tube has been off for a while, it requires a high voltage to get it started because the mercury is liquid. In this state the tube is a high impedance. Cold cathode types e. Those with a filament require their filaments to be heated, preferably for several hundred milliseconds prior to applica- tion of the high voltage; failure to preheat seriously degrades the life of the tube.
The whole electronic ballast industry got off to a bad start because early electronic ballast designers overlooked this fact. After the filaments have been heated and the high voltage has been applied, the tube turns on.
Of course, passing double the current the tube is rated for almost doubles the light output, but it also degrades the life of the tube. In this on state, the filaments still have to be heated, but with considerably less power than during preheat. Since the filaments are basically just pieces of resistive wire, this can be accomplished by reducing the filament voltage.
Other Converters The most common type of load for your converter is another switching converter. The troubles potentially associated with having two converters in series are discussed in some depth in Chapter 6 on stability.
Here it is sufficient to state that two converters, each of which is individually stable, can both oscillate if attached in series! The reason has to do with the negative input impedance of a switching converter, that is, increasing the input voltage causes the input current to decrease, because the converter is a constant power load.
It is well known that negative impedance loads are used in oscillators of many types intentional or unintentional. Power supplies often generate high voltages, or work off an AC mains.
The author feels very strongly that he would be remiss not to at least touch on a subject that is often ignored in labs under the pressure of schedules: personal safety. To start off with a true horror story, the author was once in a lab working on VAC when one of the engineers accidentally touched this voltage inside a circuit he was probing.
The engineer fell backward over the chair he was sitting on, crashed to the ground, and lay there twitching uncontrollably for a minute or more. Falling over probably saved his life, since it disconnected his hands from the line. The important thing to know is that aphoristically current is what kills, not voltage. If more than a few milliamps passes through your heart, it can fibrillate stop beating. Are your palms sweaty? This prevents current from flowing into one hand, through your heart, and to the other hand to complete the circuit.
All the time people tell me that this rule is too conservative: Its only 12V! Its only 60V! Its only VAC! L- Someone actually told me this last one. But you can actually get a nasty jolt from a 1. Its better to be safe. For the same reason, you dont want to have a good conducting path to ground: Safety Tip Wear shoes with rubber soles in the lab. This prevents current from flowing into your hand, through your heart, and down your leg to ground, completing the circuit.
Did you know that the metallic case of an oscilloscope is attached to the ground of the BNC inputs? In many labs people look at signals that are not ground-referenced by floating the oscilloscope, that is, defeating the three-wire connection on the oscilloscopes power cord by using a cheater to convert it to a two-wire connection. Unfortunately, the oscilloscopes case thus sits at the potential at which the probe ground is attached, just waiting for someone to come along and get a shock by touching it.
The 1 OMR impedance of the probe is in the signal path; the ground connection is a short. Theres a good reason that the plug is three wire, and as power engineers you should be the most familiar with it. Safety Tip Buy an isolator for the oscilloscope, and throw away all cheaters. The isolator allows each probes ground to be at any potential. If you are trying to use cheaters because of perceived noise in the system, youd better look at system grounding rather than covering it up.
Try connecting all the ground posts of the different instruments together, and attaching them to the converters return at only a single point.
Practical Lighting Design with LEDs
Download Power Supply Cookbook, Second Edition provides an easy-to-follow, step-by-step design framework for a wide variety of power supplies. With this book, anyone with a basic knowledge of electronics can create a very complicated power supply design in less than one day. With the common industry design approaches presented in each section, this unique book allows the reader to design linear, switching, and quasi-resonant switching power supplies in an organized fashion. This book also details easy-to-modify design examples that provide the reader with a design template useful for creating a variety of power supplies.
Practical design of power supplies
Applied Optics Back cover copy The second edition of Practical Lighting Design with LEDs has been revised and updated to provide the most current information for developing light-emitting diodes products. The authors, noted authorities in the field, offer a review of the most relevant topics including optical performance, materials, thermal design, and modeling and measurement. Comprehensive in scope, the text covers all the information needed to design LEDs into end products. The user-friendly text also contains numerous drawings and schematics that show how things such as measurements are actually made, and show how circuits actually work. This thoroughly expanded second edition offers: New chapters on the design of an LED flashlight, USB light, automotive taillight, and LED light bulbs Dozens of new illustrations Coverage of the nitty-gritty, day-to-day engineering and systems used to design and build complete LED systems An exploration of the cutting-edge technology of LEDs Practical Lighting Design with LEDs, Second Edition helps engineers and managers meet the demand for the surge in usage for products using light-emitting diodes with a practical guide that takes them through the relevant fields of light, electronic and thermal design.
Download Practical Design of Power Supplies - By Ron Lenk (Wiley-IEEE Press - 2005).pdf