Series for Design Engineers Brown Power Supply Cookbook, Second Edition Dostál Operational Amplifiers, Second Edition Dye Radio Frequency Transistors: Principles and Practical Applications, Second Edition Gates Energy Products Rechargeable Batteries Applications Handbook Hickman Electronic Circuits, Systems and Standards: The Best of EDN Marston Newnes Electronic Circuits Pocket Book Marston Integrated Circuit and Waveform Generator Handbook Marston Diode, Transistor and FET Circuits Manual Pease Troubleshooting Analog Circuits Sinclair Passive Components Williams Analog Circuit Design: Art, Science and Personalities Power Supply Cookbook Second Edition Marty Brown Boston Oxford Johannesburg Melbourne New Delhi Newnes is an imprint of Butterworth–Heinemann. Copyright © 2001 by Butterworth–Heinemann A member of the Reed Elsevier group All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Butterworth–Heinemann prints its books on acid-free paper whenever possible. Butterworth–Heinemann supports the efforts of American Forests and the Global ReLeaf program in its campaign for the betterment of trees, forests, and our environment. Library of Congress Cataloging-in-Publication Data Brown, Marty. Power supply cookbook / Marty Brown.—2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-7506-7329-X 1. Electric power supplies to apparatus—Design and construction. 2. Power electronics. 3. Electronic apparatus and appliances—power supply. I. Title. TK7868.P6 B76 2001 621.381¢044—dc21 00-050054 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth–Heinemann 225 Wildwood Avenue Woburn, MA 01801-2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Newnes publications available, contact our World Wide Web home page at: http://www.newnespress.com 10 9 8 7 6 5 4 3 2 1 Printed in the United States of America Power Supply Cookbook Second Edition Contents Preface ix Introduction xi 1. The Role of the Power Supply within the System and the Design Program 1.1 Getting Started. This Journey Starts with the First Question 1 1.2 Power System Organization 2 1.3 Selecting the Appropriate Power Supply Technology 3 1.4 Developing the Power System Design Specification 5 1.5 A Generalized Approach to Power Supplies: Introducing the Building-block Approach to Power Supply Design 8 1.6 A Comment about Power Supply Design Software 9 1.7 Basic Test Equipment Needed 9 2. An Introduction to the Linear Regulator 2.1 Basic Linear Regulator Operation 11 2.2 General Linear Regulator Considerations 12 2.3 Linear Power Supply Design Examples 14 2.3.1 Elementary Discrete Linear Regulator Designs 15 2.3.2 Basic 3-Terminal Regulator Designs 15 2.3.3 Floating Linear Regulators 18 3. Pulsewidth Modulated Switching Power Supplies 3.1 The Fundamentals of PWM Switching Power Supplies 21 3.1.1 The Forward-mode Converter 22 3.1.2 The Boost-mode Converter 24 3.2 The Building-block Approach to PWM Switching Power Supply Design 26 3.3 Which Topology of PWM Switching Power Supply to Use? 28 3.4 The “Black Box” Considerations for Switching Power Supplies 34 3.5 Design of the Magnetic Elements 37 3.5.1 The Generalized Design Flow of the Magnetic Elements 37 3.5.2 Determining the Size of the Magnetic Core 38 3.5.3 Designing the Forward-mode Transformer 40 3.5.4 Designing the Flyback Transformer 42 3.5.5 Designing the Forward-mode Filter Choke 46 3.5.6 Designing the Mutually Coupled, Forward-mode Filter Choke 47 3.5.7 Designing the dc Filter Choke 48 3.5.8 Base and Gate Drive Transformers 50 3.5.9 Winding Techniques for Switchmode Transformers 52 3.6 The Design of the Output Stages 56 3.6.1 The Passive Output Stage 58 v vi Contents 3.6.2 Active Output Stages (Synchronous Rectifiers) 60 3.6.3 The Output Filter 61 3.7 Designing the Power Switch and Driver Section 63 3.7.1 The Bipolar Power Transistor Drive Circuit 63 3.7.2 The Power MOSFET Power Switch 66 3.7.3 The IGBT as a Power Switch 69 3.8 Selecting the Controller IC 70 3.8.1 Short Overview of Switching Power Supply Control 71 3.8.2 Selecting the Optimum Control Method 72 3.9 Designing the Voltage Feedback Circuit. 75 3.10 Start-up and IC Bias Circuit Designs 80 3.11 Output Protection Schemes 82 3.12 Designing the Input Rectifier/Filter Section 84 3.13 Additional Functions Normally Associated with Power Supplies 90 3.13.1 Synchronization of the Power Supply to an External Source 90 3.13.2 Input, Low Voltage Inhibit 91 3.13.3 Impending Loss of Power Signal 92 3.13.4 Output Voltage Shut-down 93 3.14 Laying Out the Printed Circuit Board 93 3.14.1 The Major Current Loops 93 3.14.2 The Grounds Inside the Switching Power Supply 96 3.14.3 The AC Voltage Node 98 3.14.4 Paralleling Filter Capacitors 99 3.14.5 The Best Method of Creating a PCB for a Switching Power Supply 99 3.15 PWM Design Examples 100 3.15.1 A Board-level 10-Watt Step-down Buck Converter 100 3.15.2 Low Cost, 28 Watt PWM Flyback Converter 105 3.15.3 65 Watt, Universal AC Input, Multiple-output Flyback Converter 114 3.15.4 A 280 Watt, Off-line, Half-bridge Converter 122 4. Waveshaping Techniques to Improve Switching Power Supply Efficiency 4.1 Major Losses within the PWM Switching Power Supply 135 4.1.1 The Major Parasitic Elements within a Switching Power Supply 142 4.2 Techniques for Reducing the Major Losses 143 4.3 Snubbers 145 4.3.1 Design of the Traditional Snubber 145 4.3.2 The Passive Lossless Snubber 146 4.4 The Active Clamp 148 4.5 Saturable Inductors to Limit Rectifier Reverse Recovery Current 148 4.6 Quasi-resonant Converters 151 4.6.1 Quasi-resonant Converter Fundamentals 151 4.6.2 Quasi-resonant Switching Power Supply Topologies 155 4.6.3 Designing the Resonant Tank Circuit 156 4.6.4 Phase Modulated PWM Full-bridge Converters 161 4.7 High Efficiency Design Examples 163 4.7.1 A 10 Watt Synchronous Buck Converter 163 Contents vii 4.7.2 A 15 Watt, ZVS, Quasi-resonant, Current-mode Controlled Flyback Converter 170 4.7.3 A Zero-voltage Switched Quasi-resonant Off-line Half-bridge Converter 176 Appendix A. Thermal Analysis and Design A.1 Developing the Thermal Model 187 A.2 Power Packages on a Heatsink (TO-3, TO-220, TO-218, etc.) 189 A.3 Power Packages Not on a Heatsink (Free Standing) 190 A.4 Radial-leaded Diodes 191 A.5 Surface Mount Parts 192 A.6 Examples of Some Thermal Applications 193 A.6.1 Determine the Smallest Heatsink (or Maximum Allowed Thermal Resistance) for an Application 193 A.6.2 Determine the Maximum Power That Can Be Dissipated by a Three-Terminal Regulator at the Maximum Specified Ambient Temperature without a Heatsink 194 A.6.3 Determine the Junction Temperature of a Rectifier with a Known Lead Temperature 195 Appendix B. Feedback Loop Compensation B.1 The Bode Response of Common Circuits Encountered in Switching Power Supplies 196 B.2 Defining the Open Loop Response of the Switching Power Supply—The Control-to-Output Characteristics 201 B.2.1 The Voltage-mode Controlled, Forward-mode Converter 201 B.2.2 Flyback Converters and Current-mode Forward Converter Control-to-Output Characteristics 203 B.3 The Stability Criteria Applied to Switching Power Supplies 205 B.4 Common Error Amplifier Compensation Techniques 206 B.4.1 Single-pole Compensation 207 B.4.2 Single-pole Compensation with In-band Gain Limiting 211 B.4.3 Pole-zero Compensation 212 B.4.4 2-Pole–2-Zero Compensation 216 Appendix C. Power Factor Correction C.1 A Universal Input, 180 Watt Active Power Factor Correction Circuit 225 Appendix D. Magnetism and Magnetic Components D.1 Basic Magnetic Theory Applied to Switching Power Supplies 232 D.2 Selecting the Core Material and Style 236 viii Contents Appendix E. Noise Control and Electromagnetic Interference E.1 The Nature and Sources of Electrical Noise 241 E.2 Typical Sources of Noise 243 E.3 Enclosure Design 245 E.4 Conducted EMI Filters 245 Appendix F. Miscellaneous Information F.1 Measurement Unit Conversions 250 F.2 Wires 251 References 255 Index 257 Preface Power Supply Cookbookwas written by a practicing design engineer for practic- ing design engineers. Through designing power supplies for many years, along with a variety of electronic products ranging from industrial control to satellite systems, I have acquired a great appreciation for the “systems-level” develop- ment process and the trade-offs associated with them. Many of the approaches I use involve issues outside the immediate design of the power supply and their impact on the design. Power Supply Cookbook, Second Edition has been updated with the latest advances in the field of efficient power conversion. Efficiencies of between 80 to 95 percent are now possible using these new techniques. The major losses within the switching power supply and the modern techniques to reduce them are discussed at length. These include: synchronous rectification, lossless snubbers, and active clamps. The information on methods of control, noise control, and optimum printed circuit board layout has also been updated. As with the previous edition, the “cookbook” approach taken in Power Supply Cookbook, Second Editionfacilitates information finding for both the novice and seasoned engineer. The information is organized so that the reader need only read the material for the degree of in-depth knowledge he or she wishes to acquire. Because of the enclosed design flow, the typical power supply can be designed schematically in less than 8 hours, which can cut weeks from the expected design period. The purpose of this book is not to advance the bastions of academia, but to offer the tried and true design approaches implemented by many engineers in the power field. It offers advice and examples which can be immediately applied to the reader’s own designs. ix