ELECTRIC CIRCUITS ELECTRIC CIRCUITS Nihal Kularatna Oxford Book Company ]aipur, New Delhi ISBN: 978-93-80179-37-7 Edition: 2010 Oxford Book Company Regd. Off. 267-B, IO-B. Scheme. Opp. Narayan Niwas, Gopalpura By Pass Road. Jaipur - 302018 Rajasthan (India) Ph: 0141 - 2594705, Telefax: 2597527 B.O. 102, 1st Floor. Sat yam House. 4327/3. AnsarI Road.Darya Ganj. New Delhi - 110002 (India) Ph: 011-45652440 EmaiJ - [email protected] Visit us at: oxfordbookcompany.com © Reserved Typeset by: Slllvangl Computers 267, IO·B-Scheme, Opp Narayan Nlwas, Gopalpura By Pass Road, Jalpur-3020 18 Printed at: R'\ldhalll Pllllters, Deihl All Rights are 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, scanning or otherwise, without the prior written permission of the copyright owner. Responsibility for the facts stated. opinions expressed. conclusions reached and plagiarism, ifany. in this volume is entirely that of the Author. according to whom the matter encompassed in this book has been originally created/edited and resemblance with any such publication may be incidental. The Publisher bears no responsibility forthem. whatsoever. Preface Electronics is probably one of the few subjects where the "knowledge halflife" of a professional is very short. Today it is probably only 3 to 4 years. Designing electronic systems today requires a unique combination of (1) fundamentals; (2) research and development directions in the latest semiconductors and passive components; (3) nitty-gritty aspects within the "mixed signal world;" (4) access to component manufacturers' data. sheets, design guidelines, and development environments; and, most importantly, (5) a timely and practical approach to overall aspects of a design project. • • This work attempts to address several areas of analog and mixed signal design, including power supply design, signal conditioning, essentials of data conversion, and signal processing, while summarizing a large amount of information from theory texts, application notes, design bulletins, research papers, and technology magazine articles. In a few chapters I had the assistance of expe11s in different subject areas, as chapter authors. Nihal Kularatna Contents Preface v 1. Introduction 1 2. Transformers 24 3. Motors 64 4. Alternating Currents 71 5. Electrical Circuits: Network Analysis 92 6. Circuit Theory 105 7. Direct Current 134 8. Shock Circuits 165 9. Amplifiers' 173 10. Electrical Transients 272 Chapter 1 Introduction For an adequate understanding of the subject matter of this book, it is essential not only that the text be read and understood but especially that the reader complete all of the problems. The importance of solving the problems cannot be overstated. Some of the points in the text will seem quite obvious, and it is hoped that all of them will seem logical and understandable. However, it has been the author's repeated experience in teaching this material that people may feel that they understand it completely and yet are unable to put into practice even some of the simpler principles. If the reader really has no need to solve the problems in order to understand them, then the problems will be very easy for him. If the reader finds them hard, then they must have been needed. The general method of presentation in this book is to put basic principles and practical applications in close juxtaposition. It is certainly true that an understanding of such principles is essential to the design of new circuits, but, at the same time, understanding is not always sufficient for the successful application of these principles. Frequently, the applications must be specifically explained. A complete mastery of the concept of electric resistance helps very little in building a piece of apparatus if the builder does not know what a resistor looks like or what to do about the wires sticking out of each end. The following pages, therefore, contain almost as many pictures of actual circuit parts as circuit diagrams, and as much concrete description of elements which go into electric apparatus as discussion ofthe properties of electricity flowing through conductors. The examples discussed and the problems to be solved are drawn primarily from the behavioural sciences. Some of the most common circuit problems will be discussed specifically, so that the reader may use the solutions presented directly ifhe insists. However, this book is not intended as a handbook of solutions to common circuit problems and will not serve that function very well. Many of the problems given require the building of actual electric circuits, and a note about shock hazards might be in order here. None of the circuits to be built at the beginning of this book requires 2 Introduction more than 12 volts to operate it. It is virtually impossible to get a real shock from these circuits. In fact, except for very few circuits which-will be specifically pointed out, it is difficult even to feel a shock when trying very hard to do so. There is no need, therefore, to fear electrocution; each circuit capable of giving any shock at all will be so identified. It will be necessary to borrow or buy a number of circuit parts in order to solve the problems presented. These parts can be bought at any radio supply store, but they are all common enough so that many of them can probably be found around the laboratory. A list of these parts follows: • A 100-foot spool of solid (not stranded) hookup wire (#22 solid- type MW plastic-insulated wire, or equivalent). • Ten feet of lamp cord. • Ten alligator clips (screw connection). • A I-pound spool of rosin core solder. • Four terminal strips (at least four terminals each), lugtype, for soldering. To be screwed to board. • Four pilot light bulbs (6 volts, type 47). • Two sockets for above light bulbs. • One battery, Burgess-type 5156 "B or C" (3.4Y2, 6, 9, 10Y2, 16Y2, 22Y2 volts) clip terminals (or equivalent). • One male wall plug. • Two resistors (5 watts, 30 ohms each). • One potentiometer (10 watts, 50 ohms, wire-wound). • One potentiometer (4 watts, 5000 ohms, wire-wound). • Two set screw knobs for potentiometers. • Two capacitors (at least 150 microfarads, 50 volts, electrolytic). • Two microswitches, SPDT. • One toggle switch, DPDT. • One relay, 115 volts a-c, at least 4PDT, not enclosed (with visible working parts). • One relay, SPDT, sensitive (e.g. with at least lOOO-ohm coil resistance, closes on 10 volts or less, closes on 10 milli amperes or less), not enclosed (with visible working parts). • One toy motor (3 volts). If none of these items can be borrowed, they should not cost more than a total of about $25.00, and may be much cheaper at surplus stores. The following tools should be available: • A medium-sized screw driver. • A small soldering iron. • One pair of long-nosed pliers with wire cutters or, preferably, one pair of long-nosed pliers and a separate pair of wire cutters. Introduction 3 • One ohm-volt-ammeter. It would be most efficient if all these items were on hand before the book proper is begun rather than trying to locate each part or tool when it is first required. Many of the items listed above should be mounted on a board for convenience in setting up circuits. +Vsupply R RS OV(ground) Fig. A Board with Mounted Circuit Elements. Find a piece of wood about one foot square, and mount on it each of the components listed below. • All four terminal strips. • Two of the flashlight bulbs in their sockets. • Battery. • Both potentiometers (variable resistors). • Both microswitches. • Toggle switch. • Both relays. • Motor. The particular locations of each of these components are not important. To speed up construction of some of the simpler circuits, "clip leads" are convenient. A clip lead is a wire with an alligator clip at each end. Make five clip leads by connecting alligator clips to each end of five 12 inch­ long pieces of hookup wire. THE CONCEPT OF ELECTRICITY When you pet a cat on a dry day, both you and the cat get shocked. The reason for this is that there are loosely bonded electrons on the surface of your skin, and with your first stroke some of them are rubbed off onto the cat's fur. The cat now has more electrons than normal, and you have fewer (the cat is negatively charged, you are positive). The excess electrons 4 Introduction on the cat's fur redistribute themselves so that the charges are most dense at the tip of each hair. When you begin the next stroke, some of these electrons jump back to your hand, illustrating the fact that electrons are repelled by other electrons, and attracted by atoms that have fewer electrons than normal. The sparks that you feel and hear (and can see in a dark room) are groups of electrons jumping the gap between the tips of the cat's hairs and your hand. CURRENT AND VOLTAGE If you were to connect a wire between a petted cat and the hand that did the petting, electrons would flow through the wire from the cat to the hand. This flow of electrons is called electric current. The more electrons flowing past any point in the wire in a given time, the higher the current. If more electrons are rubbed off in the first place, the "charge" on the cat and the hand is higher, and the tendency for electrons to flow in the wire is greater. The "tendency" for current to flow between two points is called the voltage between the two points. From these crude definitions, it is clear that the higher the voltage, the greater the current, other conditions being equal.