1、TroubleshootingSwitching Power ConvertersThis page intentionally left blankTroubleshootingSwitching Power ConvertersA Hands-on GuideBySanjaya ManiktalaAMSTERDAM BOSTON HEIDELBERG LONDONNEW YORK OXFORD PARIS SAN DIEGOSAN FRANCISCO SINGAPORE SYDNEY TOKYONewnes is an imprint of ElsevierNewnes is an imp
2、rint of Elsevier30 Corporate Drive, Suite 400, Burlington, MA 01803, USALinacre House, Jordan Hill, Oxford OX2 8DP, UKCopyright 2008 by Elsevier Inc. 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, electroni
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5、oging-in-Publication DataManiktala, Sanjaya. Troubleshooting switching power converters : a hands-on guide / By Sanjaya Maniktala. p. cm. Includes bibliographical references and index. ISBN 978-0-7506-8421-7 (hardcover : alk. paper) 1. Electric current converters. 2. Semiconductor switches. 3. Switc
6、hing power supplies. I. Title. TK7872.C8M26 2007 621.317dc22 2007023364British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.ISBN: 978-0-7506-8421-7For information on all Newnes publicationsvisit our Web site at 07 08 09 10 10 9 8 7 6 5
7、 4 3 2 1Printed in the United States of AmericaWorking together to grow libraries in developing | www.bookaid.org | www.sabre.orgvContentsPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixAcknowledgments. . . . . . . . . . . . . .
8、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiiiChapter 1: Thinking Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Practice and Theory: Two Sides of the Same Coin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Leave Your Pa
9、st Perceptions Behind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Choose Your Friends Carefully. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Finding Solutions that Converge. . . . . . . . . . . . . . . . . . . . . . .
10、. . . . . . . . . . . . . . . . . . . . . 9The Ripple Effect in Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Experience Does Count; No Ifs, Ands, or Buts about That . . . . . . . . . . . . . . . . . . . . . . . 11Never Ignore a Problem Until It Is
11、Too Late . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Know Your Instruments Well . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Heatseekers: On the Road with Symptomatic Troubleshooting. . . . . . . . . . . . . . . . . . . . 14C
12、ausality Can Be the First Casualty. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19To “Errr” Is Human. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Learn from (Their) Mistakes. . . . . . . . . . . . . .
13、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25The Problem with Problem Solving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Chapter 2: High-Frequency Effects and the Importance of Input Decoupling . . . . 33Lies, Damn Lies, and Schematics
14、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Occupational Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Watch the Feedback Trace Closely. . . . . . . . . . . . . . . . . . . . . . . . . . .
15、 . . . . . . . . . . . . . . . 44Physical Distances Become Critical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Estimating Harmonic Amplitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47High-Frequency Input Decoupli
16、ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Dont Forget to Place that 0.1F Ceramic Capacitor Really Close to the IC . . . . . . . . . 49You Need Bulk Capacitance, Too . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
17、Where Is the “Missing” Current Coming From? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Check Your Bench Power Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Lack of Bulk Capacitance and/or Too Much ESR Can Play Havoc . . . . . . . .
18、 . . . . . . . . 56Single Ceramic Capacitor for Both Noise and Ripple? . . . . . . . . . . . . . . . . . . . . . . . . . . 58viThe Control Also Needs a Clean Supply Rail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Boost Topology Decoupling Is Slightly Different . . . . . . .
19、. . . . . . . . . . . . . . . . . . . . . . . 60Chapter 3: Output Noise and Filtering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Measuring Output Noise and Ripple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Chapter 4: Using Capacitors Wise
20、ly. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Part 1: Aluminum Electrolytics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21、 . . . . . . . . . . . . . 79Part 2: Ceramic Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Chapter 5: Maximizing the Effectiveness of the Ground Plane. . . . . . . . . . . . . . . 109How to Parallel Output Capacitors for Proper Sharing .
22、 . . . . . . . . . . . . . . . . . . . . . . . . . 109Integrated Switcher IC Solutions Versus Controller IC Solutions . . . . . . . . . . . . . . . . . . 114Quick Check on Current through Aluminum Capacitors . . . . . . . . . . . . . . . . . . . . . . . . . 114Secondary Side Trace Inductances and Th
23、eir Impact on Effi ciency . . . . . . . . . . . . . . . . 115Current Return Paths in the Ground Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Paralleling Traces to Reduce Inductance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120Chapte
24、r 6: Printed Circuit Board Layout for AC-DC and DC-DC Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Evaluati
25、on Boards (EVBs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Chapter 7: Working without a Ground Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 149384x-based Controllers on Single-sided Boards. . . . . . . . . . . . . . . . . . . .
26、. . . . . . . . . . . . 149Watch the Primary Side Current Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151And the Secondary Side Current Loop, Too. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152The Real “Switch”. . . . . . . . . . . . .
27、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157Chapter 8: Home-Grown Strategies in Troubleshooting. . . . . . . . . . . . . . . . . . . . 161Peeling the Onion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
28、 . . . . 161Chapter 9: Effective Bench Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Basic Equipment . . . . . . . . . . . . . . .
29、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189Chapter 10: Effi ciency Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207Ensure the Drive Is Adequate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30、 . . . . . . . . 207Minimize Capacitive Parasitics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210ContentsviiProper Design of Snubbers and Clamps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212Varying the Frequency. . . . .
31、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216The Time-sharing Principle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216Understanding the Shape of Buck Effi ciency Curves. . . . . . . . . . . . . .
32、. . . . . . . . . . . . . . 218Estimating the Ratio of Conduction Loss to Switching Loss. . . . . . . . . . . . . . . . . . . . . . 221Chapter 11: Magnetics, EMI, and Noise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229The Wish List . . . . . . . . . . . . . . . . . . . . . . . . .
33、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229Twisting and Turning Your Way Out of EMI Problems. . . . . . . . . . . . . . . . . . . . . . . . . . 233Location of Clamp Affects Noise, Too . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238A Cheat-
34、sheet for EMI Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239Chapter 12: Discussion Forums, Datasheets, and Other Real-World Issues. . . . . 247Thinking Is the Key. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
35、. . . . . . . . . 247Cross-check Everything. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247Product Liability Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Its All about the Customer
36、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250The Q&A Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37、. . . . . . . . . . . . . . . . . . . . . . . 291Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293ContentsThis page intentionally left blankixPrefaceA few weeks ago, I found myself groping for some sorely needed inspiration. I
38、 was even questioning the very need for a book on this particular subject. So despite spending fi ve years in the general vicinity of the legend behind it, I fi nally went and bought myself the “other” bookTroubleshooting Analog Circuits by Robert Pease. I am glad I did, because it ended up fulfi ll
39、ing both my requirementsI not only learned that his book is truly is an inspiring resource (certainly something to chuckle your way through coach class with pretzels and coffee in hand), but also that it isnt about Power Conversion. Take, for example, that famous picture on its cover. The hopelessly
40、 entangled object you see there (the creation, not the creator) apparently served as a historic V-F (voltage-to-frequency) converter circuit. But really, it would never pass muster as even a basic switching converter. Breadboards, for one, are kryptonite to switching converters. If you really think
41、about it, all that that picture so aptly conveys is exactly what you shouldnt ever be attempting to do in power. Reassuringly, even that book itself recognizes that “switch-mode regulators are a whole new ball-game.”So it was surprising for me to learn that the analog troubleshooting book was origin
42、ally intended to be just a single chapter of a much larger volume on the topic of switching power converters. Maybe that project just slipped through the cracks of time. Perhaps it was too diffi cult a venture to undertakea hypothesis somewhat supported by the fact that there is still virtually no o
43、ther book out there on this topic (cheers to the book youre holding, by the way!). But I also tend to believe that if it were published in the format it seems to have been originally conceived in, it could well have turned out to be quite misleadingfor reasons very similar to that on the cover of th
44、e analog book. For a while, that had me seriously thinking: “whose bright idea was that?” Then I realized that back in those days, Power Conversion was still in its infancy. Who knew what lay ahead?In the early 1970s, the Intel 8080 microprocessor was dazzling engineers around the world with its bla
45、zing computational speed of 2MHz! “Digital” became the anthem for a new Prefacexgeneration of EE graduates. Virtually every prospective hire our company interviewed in that decade (and the next), when asked what he or she would like to do for the company, said without a blink“Microprocessor!” I thin
46、k I probably got to do Power only because I was not considered good enough for all the really “good stuff.” Though a little later I think things must have soured for some of the laggards involved in this digital race, individuals and companies alike. And in the resulting reverse pileup, somehow ever
47、ything non-digital suddenly got crowned “analog.”I wonder how that happened. Catchy phrases such as “the power of analog” may have tickled the collective imagination, but at best they were just oxymorons (quite appropriately with a “moron” in it!). Because, despite all their apparent familiarity and
48、 similarity, “Analog” and “Power” are actually strange bedfellows. You just cant club them together in one grand compendium titled “Everything you didnt want to know about digital circuits . . . and werent afraid to ask.” Yes, though both analog and power have certain commonalities, in that they are
49、 both essentially “non-digital,” the similarity ends right there. The distinguishing characteristic of modern switching power converters is that their sharp edges of current and voltage, driven by an almost mystically endowed inductor, generate so much high-frequency content that all the hitherto painfully learned rules of the game tumble helplessly to the ground (quite literally so).“Analog or Power, whats in a name?” you may well ask. One practical problem arising from that lack of dichotomy is that in many companies, senior managers suddenly arrive almost unheralded on the scene, possessed
