THE FIELDS OF ELECTRONICS

Transcription

1 THE FIELDS OF ELECTRONICS

2 THE FIELDS OF ELECTRONICS Understanding Electronics Using Basic Physics Ralph Morrison A Wiley-Interscience Publication JOHN WILEY & SONS, INC.

3 This book is printed on acid-free paper.!" Copyright c! 2002 by John Wiley & Sons, Inc., New York. All rights reserved. Published simultaneously in Canada. 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, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) , fax (978) Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 605 Third Avenue, New York, NY , (212) , fax (212) , PERMREQ@WILEY.COM. For ordering and customer service, call CALL-WILEY. Library of Congress Cataloging-in-Publication Data Is Available ISBN Printed in the United States of America

4 CONTENTS Preface xi 1 The Electric Field Introduction Charge Electrical Forces on Charged Bodies Electric Field Work Voltage Charges on Surfaces Equipotential Surfaces Field Units Batteries A Voltage Source Current Resistors Resistors in Series or Parallel E Field and Current Flow Problems Energy Transfer Resistor Dissipation Problems Electric Field Energy Ground and Ground Planes Induced Charges Forces and Energy Problems Review 21 2 Capacitors, Magnetic Fields, and Transformers Dielectrics Displacement Field 23

5 vi CONTENTS 2.3 Capacitance Capacitance of Two Parallel Plates Capacitance in Space Current Flow in Capacitors RC Time Constant Problems Shields Magnetic Field Solenoids Ampère s Law Problems Magnetic Circuit Induction or B Field Magnetic Circuit without a Gap Magnetic Circuit with a Gap Transformer Action Magnetic Field Energy Inductors L=R Time Constant Mutual Inductance Problems Review 44 3 Utility Power and Circuit Concepts Sine Waves Reactance and Impedance Problems Resonance Phase Parallel RL and RC Circuits Problems RMS Values Problems Transmission Lines Poynting s Vector Transmission Line over an Equipotential Surface Transmission Lines and Sine Waves Coaxial Transmission Utility Power Distribution 62

6 CONTENTS vii 3.16 Earth as a Conductor Power Transformers in Electronic Hardware Electrostatic Shields in Electronic Hardware Where to Connect the Metal Box Problems Review 74 4 A Few More Tools Introduction Resistivity Inductance of Isolated Conductors Ohms per Square Problems Radiation Half-Dipole Antennas Current Loop Radiators Field Energy in Space Problems Reflection Skin Effect Problems Surface Currents Ground Planes and Fields Apertures Multiple Apertures Waveguides Attenuation of Fields by a Conductive Enclosure Gaskets Honeycombs Wave Coupling into Circuits Problems Square Waves Harmonic Content in Utility Power Spikes and Pulses Transformers Eddy Currents Ferrite Materials 99

7 viii CONTENTS 4.30 Problems Review Analog Design Introduction Analog Signals Common-Mode Interference Common-Mode Rejection in Instrumentation Problems Voltage Measurement: Oscilloscopes Microphones Resistors Guard Rings Capacitors Problems Feedback Processes Problems Miller Effect Inductors Transformers Problems Isolation Transformers Solenoids and Relays Problems Power Line Filters Request for Energy Filter and Energy Requests Power Line Filters above 1 MHz Mounting the Filter Optical Isolators Hall Effect Surface Effects Review Digital Design and Mixed Analog/Digital Design Introduction Logic and Transmission Lines Decoupling Capacitors Ground Planes 131

8 CONTENTS ix 6.5 Power Planes Decoupling Power Geometries Ground Plane Islands Radiation from Loops Problems Leaving the Board Ribbon Cable and Common-Mode Coupling Braided Cable Shields Transfer Impedance Mechanical Cable Terminations Problems Mounting Power Transistors Electrostatic Discharge ESD Precautions Zapping Product Testing: Radiation Military Testing Chattering Relay Test Euro Standards LISN Sniffers Simple Antenna Peripherals Problems Lightning Problems Mixing Analog and Digital Design Ground Bounce Review Facilities and Sites Introduction Utility Power Floating Utility Power Isolated Grounds Single-Point Grounding Ground Planes Alternative Ground Planes Power Centers 157

9 x CONTENTS 7.9 Lightning Protection Surge Suppression Racks Magnet Fields around Distribution Transformers Monitor Fields Motor Controllers Screen Rooms Review 164 Appendix I: Solutions to Problems 165 Appendix II: Glossary of Common Terms 177 Appendix III: Abbreviations 183 Index 187

10 PREFACE This book provides a new way to understand the subject of electronics. The central theme is that all electrical phenomena can be explained in terms of electric and magnetic fields. Beginning students place their faith in their early instruction. They assume that the way they have been educated is the best way. Any departure from this format just adds complications. This book is a departure hopefully, one that helps. There are many engineers and scientists struggling to function in the real world. Their education did not prepare them for handling most of the practical problems they encounter. The practitioner in trouble with grounds, noise, and interference feels that something is missing in his education. The new engineer has a very difficult time ordering, specifying, or using hardware correctly. Facilities and power distribution are a mystery. Surprisingly, all these areas are accessible once the correct viewpoint is taken. This book has been written to provide a better introduction to the field of electronics so that the parts that are often omitted can be put into perspective. The book uses very little mathematics. It helps to have some background in electronics, but it is not necessary. The beginning student may need some help from an instructor to fill in some of the blanks. The practicing engineer will be able to read this book with ease. Field phenomena are often felt to be the domain of the physicist. In a sense this is correct. Unfortunately, without a field-based understanding, many electronic processes must remain mysteries. It is not necessary to solve difficult problems to have an appreciation of how things work. It is only necessary to appreciate the fundamentals and understand the true nature of the world. To illustrate the problem, consider an electric field that is constant everywhere. Place a conducting loop of wire at some crazy angle in this field and ask a question: What is the shape of the new field? This is a very difficult problem even with a great deal of computing power. Now, have the field change sinusoidally and consider current flow and skin effect and the problem really gets difficult. The ideas are important, but the exact answer is not worth worrying about. Connecting wires and components to form circuits is standard practice. These conductors modify the fields around them. This is the same nasty problem, and again it does not need an exact solution. What is needed is an understanding of what actually takes place. Circuit theory does not consider this type of problem.

11 xii PREFACE Most students in electronics spend a great deal of time with circuit theory. The viewpoint of circuit theory is to treat lumped-parameter models. Circuit theory provides an excellent way to predict the behavior of a group of components. The mathematics is very straightforward. Field theory, on the other hand, provides very little in terms of simple answers. Most practical problems cannot be approached by field theory, and yet circuit theory and field theory are inseparable. Circuit theory has no way to handle component size or orientation. Circuit theory, with its zero-ohm connections, avoids any reference to loop area, common-impedance coupling, or common-mode coupling. It fails to reference radiated energy from any source. Circuit theory has its successes, but it also has its failures. Field theory has its place, too, and yet it fails, as there is no convenient methodology. Educators are oriented toward problem-solving courses. Circuit theory fits this model, as it lends itself to solving many practical problems. Electricity and magnetism courses are more difficult, and only very simple geometries can be approached. The mathematics of vector fields, complex variable, and partial differential equations are not for the faint of heart. This leaves the practicing engineer with one solution. Drop physics and concentrate on circuit theory to provide answers. The circuit diagram of a building or the grounding diagram of a power grid is of no help in analyzing interference. These diagrams can be attempted, but they fail to provide a useful approach. They do not fit the textbook models, as they are not lumped-parameter circuits. The engineer is at a loss. This book allows the student to solve problems by means of simple ratios. In each area, typical practical problems are solved in the text. The student is expected to use this information to work the problem sets. The answers are all worked out in Appendix I. This makes it possible for the engineer or technician out of school to use the book for self-study. It also makes it possible to use the text in school, where problems can be assigned. The teacher can modify the parameters in the problems so that the student must work out the details rather than copy the answers. This book is not intended to teach circuit theory. It is not a substitute for teaching physics. It is a tool that can be used to connect the two subjects. There is a need to establish an elementary understanding in both areas so that the reader can understand the things that occur in the real world. This is done in the early chapters. The problems that are discussed throughout the book occur frequently. Exact solutions are not attempted. The simplifications that are applied are brought out in the text. These simple approaches provide insight into what can be done to handle practical situations. If students want to study physics or expand their knowledge of circuit theory, many texts and courses are available. This book takes the liberty of choosing important features from both areas in order to provide students with a different view of the electrical world a view from the bridge between electrical behavior and physics. Redwood City, CA February 14, 2001 Ralph Morrison