Power Electronics Semiconductor Switches978-1-4757-6219-8/1.pdf · Chapter 4 THE BJT TRANSISTOR 123...

Power Electronics Semiconductor Switches

Power Electronics Semiconductor Switches

R.S. Ramshaw

Department of Electrical and Computer Engineering University of Waterloo

Ontario Canada

SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

ISBN 978-0-412-28870-8 ISBN 978-1-4757-6219-8 (eBook) DOI 10.1007/978-1-4757-6219-8

First edition 1993

© 1993 R.S. Rarnshaw Originally published by Chapman & Hall in 1993 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the OK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page.

The publisher makes no representation, express or implied. with regard to the accuracy of the information conlained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication data available

§ Printed on permanent acid-free text paper, manufactured in accordance with the proposed ANSIINISO Z 39.48-199X and ANSI Z 39.48-1984

CONTENTS

PREFACE xiii

Chapter 1 POWER CONDITIONING 1

1.1. Introduction 1 1.2. Power Electronics 1 1.3. Power Modulation 2

1.3.1. DC Supplies to a Load 3 1.3.2. AC Supplies to a Load 6

1.4. Waveform Distortion 12 1.4.1. Average Values 12 1.4.2. RMS Values 13 1.4.3. Form Factor 14 1.4.4. Harmonics 14 1.4.5. Total Harmonic Distortion (THD) 16 1.4.6. Average Power 16

1.5. Power Semiconductor Switches 18 1.6. Applications 22 1.7. Summary 23 1.8. Problems 23

Chapter 2 SWITCHES IN CIRCUITS 25

2.1. Introduction 25 2.2. DC to DC Conversion 26

2.2.1. Buck Converter 27 2.2.2. Boost Converter 29

2.3. AC to DC Conversion 32 2.3.1. Converter Performance and Operation Modes 32 2.3.2. Single-phase Half-wave Converter 36 2.3.3. Single-phase Bridge Converter 45

2.4. DC to AC Conversion 51 2.4.1. Centre-tapped Source Inverter 54 2.4.2. Single-phase Bridge Inverter 64 2.4.3. Three-phase Inverters 74

2.5. Summary 82 2.6. Problems 83 2.7. Bibliography 89

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Chapter 3 THE DIODE 90

3.1. Introduction 90 3.2. Diode Structure 92 3.3. Diode I-V Characteristics 92

3.3.1. Forward Bias 92 3.3.2. Reverse Bias 94 3.3.3. Ideal Diode 95

3.4. Diode Models 96 3.5. Diode Turn-on 98 3.6. Diode Turn-off 99 3.7. Diode Protection 103

3.7.1. Overcurrent 103 3.7.2. Overvoltage 104 3.7.3. Transients 104

3.8. Diode Ratings Applications and Analysis 107 3.8.1. Ratings 108 3.8.2. Rectification 108

3.9. Diodes in Parallel and Series 117 3.10. Summary 118 3.11. Problems 119 3.12. Bibliography 122

Chapter 4 THE BJT TRANSISTOR 123

4.1. Introduction 123 4.2. BJT Structure 125 4.3. BJT I-V Characteristics 126

4.3.1. Ideal Switch 126 4.3.2. Nonideal Switch 127

4.4. BlTModels 132 4.5. BJT turn-on 133

4.5.1. Turn-on Action 133 4.5.2. Tum-on Losses 134

4.6. BJT Turn-off 139 4.6.1. Tum-off Losses 141 4.6.2. Current Focusing 145

4.7. BlT Power Dissipation 146 4.8. BJT Base Drive 149

4.8.1. Baker Clamp 151 4.9. BJT Protection 153

4.9.1. Overcurrent 153 4.9.2. Overvoltage 153

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4.9.3. Safe Operating Area (SOA) 4.9.4. Transients

4.10. BJT Ratings and Applications 4.10.1. Applications

4.11. Summary 4.12. Problems 4.13. Bibliography

Chapter 5 THE THYRISTOR

5.1. Introduction 5.2. Thyristor Structure 5.3. Thyristor Models

5.3.1. Diode Model of the Thyristor 5.3.2. Two-transistor Model of the Thyristor

5.4. Thyristor I-V Characteristics 5.5. Thyristor Turn-on

5.5.1. Turn-on Losses 5.5.2. Turn-on Circuits

5.6. Thyristor Turn-off 5.6.1. Turn-off Circuits

5.7. Thyristor Power Dissipation 5.8. Thyristor Ratings 5.9. Thyristor Protection

5.9.1. Main Power Circuit 5.9.2. Gate Protection

5.10. Thennal Considerations 5.10.1. Thennal Resistance 5.10.2. Transient Thennal Impedance

5.11. Thyristors in Series and Parallel 5.11.1. Thyristors in Series 5.11.2. Thyristors in Parallel

5.12. Summary 5.13. Problems 5.14. Bibliography

154 155 158 160 167 167 172

173

173 174 175 175 176 177 178 183 188 199 202 210 211 214 215 218 219 219 222 227 228 231 235 236 242

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Chapter 6 THE MOSFET 244

6.1. Introduction 244 6.2. MOSFET Structure 246 6.3. MOSFET I-V Characteristics 250 6.4. MOSFET Models 253 6.5. MOSFET Turn-on 256

6.5.1. Turn-on Action 256 6.5.2. Turn-on Losses 260

6.6. MOSFET Turn-off 268 6.6.1. Turn-off Losses 268

6.7. MOSFET Gate Circuits 275 6.8. MOSFET Protection 279

6.8.1. Overvoltages 279 6.8.2. Overcurrents 280 6.8.3. Transients 284

6.9. MOSFET Ratings and Applications 286 6.10. Summary 288 6.11. Problems 289 6.12 Bibliography 293

Chapter 7 THEIGBT 294

7.1. Introduction 294 7.2. IGBT Structure 295 7.3. IGBT I-V Characteristics 297 7.4. IGBT Model 300 7.5. IGBTTurn-on 302

7.5.1. Turn-on Losses 303 7.6. IGBT Turn-off 307

7.6.1. Turn-off Losses 308 7.7. IGBT Protection 312

7.7.1. Overvoltages 312 7.7.2. Overcurrent 313 7.7.3. Transients 316

7.8. IGBT Ratings and Applications 317 7.9. Summary 319 7.10. Problems 320 7.11. Bibliography 323

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ChapterS THETRIAC 324

8.1. Introduction 324 8.2. Triac Structure 324 8.3. Triac Model 325 8.4. Triac I-V Characteristics 326 8.5. Triac Turn-on 329

8.5.1. Turn-on Action 330 8.5.2. Turn-on Losses 333 8.5.3. Turn-on Circuits 335

8.6. Triac Turn-off 338 8.7. Triac Ratings 340

8.7.1. Thermal Ratings 341 8.8. Triac Protection 341 8.9. Triac Applications 343

8.9.1. AC-AC Conversion 343 8.9.2. AC-DC Conversion 349

8.10. Summary 349 8.11. Problems 349 8.12. Bibliography 353

Chapter 9 THEGTO 354

9.1. Introduction 354 9.2. GTO Structure 355 9.3. G TO I-V Charac teris tics 356 9.4. GTO Two-transistor Model 359 9.5. GTOTurn-on 361 9.6. GTO Turn-off 364 9.7. GTO Gate Circuits 370 9.8. GTO Protection 372 9.9. GTO Ratings and Applications 375 9.10. Summary 381 9.11. Problems 382 9.12. Bibliography 385

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Chapter 10 OTHER SWITCHES AND THE MCT 386

10. I. Introduction 386 10.2. The SIT 387

10.2.I. SIT Structure 387 10.2.2. SIT I-V Characteristics 388 10.2.3. SIT Turn-off 389 10.2.4. SIT Turn-on 390 10.2.5 SIT Protection 390 10.2.6. SIT Ratings and Applications 390

10.3. The SITH 391 1O.3.I. SITH Structure 391 10.3.2. SITH I-V Characteristics 392 10.3.3. SITH Turn-off 393 10.3.4. SITH Turn-on 394 10.3.5. SITH Protection 394 10.3.6. SITH Ratings and Applications 395

10.4. Thyristors 395 10.4. I. The ASCR 395 10.4.2. TheGATI 396 10.4.3. TheRCT 396

10.5. TheMCT 397 1O.S.I. MCT Structure 398 10.5.2. MCT I-V Characteristics 399 10.5.3. MCTModels 400 10.5.4. MCTTurn-on 401 10.5.5. MCTTurn-off 401 10.5.6. MCT Protection 403 10.5.7. MCT Ratings and Applications 404

10.6. Summary 406 10.7. Problems 407 10.8. Bibliography 409

APPENDIX 1 Rectifier Diode Data Sheets 410

APPENDIX 2 BJT Power Transistor Data Sheets 414

APPENDIX 3 Power MOSFET Data Sheets 418

APPENDIX 4 Thyristor Data Sheets 426

APPENDIX 5 IGBT Data Sheets 430

APPENDIX 6 Triac Data Sheets 434

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APPENDIX 7 GTO Data Sheets

APPENDIX 8 MeT Data Sheets

APPENDIX 9 Answers to Problems

APPENDIX 10 List of Symbols

INDEX

436

440

444

449

454

PREFACE

Power electronics plays a significant role in the application of electric power wherever there is a need to change voltage, .current or frequency from the stan­dard values that are available. At the heart of power electronics is a fast acting switch that is used, not just to isolate the source from the load, but to modulate the power that reaches the load.

This is an introductory text about semiconductor switches and their uses to modulate power to a form best suited to a load. Today the subject of power elect­ronics has expanded to include not only power semiconductor devices, but also to incorporate converter topologies, analysis and simulation, control and estimation techniques and control hardware together with the attendant software. Each of these is a topic in its own right and is left for further study following this text.

In the first part of the text there is a description of how power is converted from ac to dc, ac to ac, dc to dc and dc to ac forms in the terms of the periodic opening and closing of a single switch or a group of switches that are ideaL That is, the basics of power conditioning are generalized.

In the second part of the text, systems of supply, converter and load are described. The equations that govern the behaviour of those converters with ideal switches are formulated to provide the fundamentals of the analysis of power con­ditioning in basic circuits. The result is twofold. The basic responses of currents voltages and average power are determined for the input and output of the conver­ter, starting with the simplest load and progressing to complex passive loads. Fur­ther, the performance factors that describe the goodness of power conversion are applied to each type of converter. This description is broadly based with simple analytical treatments of simple systems to show in first principles what is possible to be done with more complex switching systems.

With this background to the use of semiconductor switches, the important switches are treated separately in the third and main part of the text. The purpose is to help the reader make a choice of the right switch for a particular application and to help in the use of the switches in circuits. For each switch there is a description of operation in general terms of a pn junction and charge flow under the influence of electric fields. The physics of operation is omitted, because the text is aimed at those who may have the desire to use switches in a converter. Cir­cuit operation and switch control are the important objectives of this text.

No switch is perfect. Accordingly, some attempt is made to accentuate the per­formance characteristics of the switch in terms of steady-state and transient opera­tion. From this, the main forms of protection become evident.

Design techniques for circuits and systems that incorporate switches are left to manufacturers' manuals. The analytical descriptions, that are given in this text, are mainly to show the principles of switch and circuit behaviour and to provide a

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base so that manufacturers' data sheets and manuals can be used to the best effect. The best effect usually means minimum losses and waveforms as close to the ideal as possible.

This book is intended as a text for readers who wish to become users of semi­conductor switches and who wish to understand basics of power electronics and switch applications. It is for this reader that there are many worked examples and many more problems for practice. Hands-on experience quickly shows the fragil­ity and limitations of power electronics circuits, just like solving problems enables rapid learning of principles and an acknowledgement of the limitations of our modelling and analytical tools. Many of the problems make use of chopper circuits to exemplify a switch's performance, because choppers provide extreme characteristics that are relatively easy to analyze.

Although this book sets out to be a first course in the subject of power electron­ics, it does rely on the readers' familiarity with a fundamental electrical engineer­ing course in circuit theory and its attendant mathematics. The level of analysis has increased in recent years. The knowledge of mathematics that is required has not changed much, but the complexity of the switched-circuit analysis has been extended by the availability of mathematical tools for computer aided analysis. There are software packages (MATLAB, MATHCAD etc.) available to take away the drudgery of solving a transcendental equation and to solve problems of Fourier analysis, of complex integrals or simultaneous transcendental equations that might have been left alone before.

As this book is an introductory text, the bibliography given at the end of each chapter is an invitation for further reading.

Acknowledgement and gratitude are due to Elizabeth Nicklin who has taken the author's scribblings and sketches and transformed them into the typeset text and figures set before you. The University of Auckland kindly provided the facilities for the preparation of the text. At the University of Auckland James Thompson was kind enough to solve many of the MATLAB problems and Grant Spencer gave his time generously to proof-read the final draft. Thanks are due to Philips Export B.V. and Harris Semiconductor for giving permission to reproduce their data sheets.

Raymond Ramshaw Waterloo.