开关电源供应器.pdf

Switching Power Supplies A to ZThis Page Intentionally Left BlankSwitching Power Supplies A to ZSanjaya ManiktalaAMSTERDAM BOSTON HEIDELBERG LONDONNEW YORK OXFORD PARIS SAN DIEGOSAN FRANCISCO SINGAPORE SYDNEY TOKYONewnes is an imprint of ElsevierNewnes is an imprint of Elsevier30 Corporate Drive,Suite 400,Burlington,MA 01803,USALinacre House,Jordan Hill,Oxford OX2 8DP,UKCopyright 2006,Elsevier Inc.All rights reserved.No part of this publication may be reproduced,stored in a retrieval system,or transmitted in any formor by any means,electronic,mechanical,photocopying,recording,or otherwise,without the priorwritten permission of the publisher.Permissions may be sought directly from Elseviers Science&Technology Rights Department inOxford,UK:phone:(+44)1865 843830,fax:(+44)1865 853333,E-mail:.You may also complete your request on-line via the Elsevier homepage(http:/),byselecting“Support&Contact”then“Copyright and Permission”and then“Obtaining Permissions.”Recognizing the importance of preserving what has been written,Elsevier printsits books on acid-free paper whenever possible.Library of Congress Cataloging-in-Publication DataApplication SubmittedBritish Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.ISBN 13:978-0-7506-7970-1ISBN 10:0-7506-7970-0For information on all Newnes publicationsvisit our Web site 06 07 08 09 1010 9 8 7 6 5 4 3 2 1Printed in the United States of AmericaContentsPreface.xiAcknowledgements.xviiChapter 1:The Principles of Switching Power Conversion.1Introduction.3Overview and Basic Terminology.5Understanding the Inductor.22Evolution of Switching Topologies.43Chapter 2:DC-DC Converter Design and Magnetics.61DC Transfer Functions.64The DC Level and the“Swing”of the Inductor Current Waveform.65Defining the AC,DC,and Peak Currents.68Understanding the AC,DC and Peak Currents.70Defining the“Worst-case”Input Voltage.72The Current Ripple Ratio r.75Relating r to the Inductance.75The Optimum Value of r.77Do We Mean Inductor?Or Inductance?.79How Inductance and Inductor Size Depend on Frequency.80How Inductance and Inductor Size Depend on Load Current.80How Vendors Specify the Current Rating of an Off-the-shelf Inductor andHow to Select It.81What Is the Inductor Current Rating We Need to Consider for a Given Application?.82The Spread and Tolerance of the Current Limit.85Worked Example(1).88Worked Examples(2,3,and 4).100Worked Example(5)When Not to Increase the Number of Turns.106Worked Example(6)Characterizing an Off-the-shelf Inductor in aSpecific Application.110Calculating the“Other”Worst-case Stresses.118vContentsChapter 3:Off-line Converter Design and Magnetics.127Flyback Converter Magnetics.130Forward Converter Magnetics.152Chapter 4:The Topology FAQ.177Questions and Answers.179Chapter 5:Conduction and Switching Losses.203Switching a Resistive Load.206Switching an Inductive Load.210Switching Losses and Conduction Loss.213A Simplified Model of the Mosfet for Studying Inductive SwitchingLosses.215The Parasitic Capacitances Expressed in an Alternate System.217Gate Threshold Voltage.218The Turn-on Transition.218The Turn-off Transition.222Gate Charge Factors.224Worked Example.227Applying the Switching Loss Analysis to Switching Topologies.231Worst-case Input Voltage for Switching Losses.232How Switching Losses Vary with the Parasitic Capacitances.233Optimizing Driver Capability vis-vis Mosfet Characteristics.234Chapter 6:Printed Circuit Board Layout.237Introduction.239Trace Section Analysis.239Some Points to Keep in Mind During Layout.240Thermal Management Concerns.247Chapter 7:Feedback Loop Analysis and Stability.249Transfer Functions,Time Constant and the Forcing Function.251Understanding e and Plotting Curves on Log Scales.252Time Domain and Frequency Domain Analysis.255Complex Representation.256Nonrepetitive Stimuli.258The s-plane.258Laplace Transform.260viContentsDisturbances and the Role of Feedback.262Transfer Function of the RC Filter.264The Integrator Op-amp(“pole-at-zero”filter).267Mathematics in the Log Plane.269Transfer Function of the LC Filter.270Summary of Transfer Functions of Passive Filters.273Poles and Zeros.274Interaction of Poles and Zeros.276Closed and Open Loop Gain.277The Voltage Divider.280Pulse Width Modulator Transfer Function(gain).281Voltage Feedforward.282Power Stage Transfer Function.283Plant Transfer Functions of All the Topologies.284Boost Converter.286Feedback Stage Transfer Functions.289Closing the Loop.291Criteria for Loop Stability.293Plotting the Open-loop Gain and Phase with an Integrator.293Canceling the Double Pole of the LC Filter.295The ESR Zero.296Designing a Type 3 Op-amp Compensation Network.297Optimizing the Feedback Loop.301Input Ripple Rejection.304Load Transients.305Type 1 and Type 2 Compensations.306Transconductance Op-amp Compensation.308Simpler Transconductance Op-amp Compensation.311Compensating with Current Mode Control.313Chapter 8:EMI from the Ground up Maxwell to CISPR.323The Stand