alee) Martin Podges edad Ld a edAcknowledgements The authors and publishers wish to thank the following persons and institutions for their invaluable contribution to the development of this publication and for permission to reproduce material: * The United States Agency for International Development (USAID), for funding the project. This Materials Development Project formed part of the Tertiary Education Linkages Project (TELP) which focused on capacity building at Historically Disadvantaged Technikons through the establishment of linkages with universities in the United States of America. * Contributors and moderators from the following South African institutions: Mangosuthu Technikon, ML Sultan Technikon, Peninsula Technikon, Technikon Eastern Cape, Technikon Northern Gauteng, Technikon Southern Africa. + Contributors and moderators from the United States University Consortium comprising Howard University, Massachusetts Institute of Technology, Clark Atlanta University, and North Carolina A&T State University. * The Motorola Corporation, Atlanta, USA, for permission to reproduce the data sheets on pages 75, 85, 86, 89, 180-182 and 200-201. Various people have been involved in the development of this book, and I would like to thank them for their invaluable contributions: Jan Hattingh (Bothurpe Hellerman) for supplying photographs of the instruments on pages 2, 3, 8, 19, 20, 21 and 197; Abrie Michau and Pam Pike (TSA); and all my colleagues at Eastern Cape Technikon for their support with this project. } Martin Podges First published 1999 © Juta & Co, Ltd 1999 PO Box 14373, Kenwyn 7790 ISBN 0 7021 5214 5 This book is copyright under the Berne Convention. In terms of the Copyright Act 98 of 1978, no part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording. or by any information storage and retrieval system, without permission in writing from the Publisher. Illustrator: Hugh Lane, Malick Abarder Book design: Designworx Typesetting: AN dtp Services Cover design: Pumphaus Design Studio Printed and bound in South Africa by The Rustica Press, Ndabeni, Western Cape DeeContents Note to the student ix ee ee | Outcomes 1 L1_Introduetion 2 L2__Multimeters 2 1.2.1 Analog multimeters 2 1.2.2 Digital multimeters 3 > Basic operation 3 & Voltage measurements 3 & Current measurements 4 & Resistance measurements 4 & Range selection 5 & Comparison 6 Activity If 7 1.3 Oscilloscopes 8 1.3.1 Basic operation 8 b> Cathode ray tube (CRT) b> The sweep generator 10 & The vertical attenuator and vertical amplifier TZ b Triggering 12 1.3.2 Oscilloscope measurements Is & Voltage (ac and de) 15 _Period or frequency 16 1.3.3 Setting up an oscilloscope 17 Activity L2 19 1.4 Function generators 19 Activity 1.3 20 1.5 The de power supply 20 Activity 1.4 22 L6__Breadboards 4. Activity 1.5 23 1.7 Summary 23 Selfevaluation 0 Answers. 27Unit 2 Semiconductor theor | 2.1 Introduction | > 2.2.2 Valence band 32 2.2.3 Jonisation 33 2.2.4 Energy bands 33 Activity 2.1 34 2.3 Semiconductors 8 2.3.1 Covalent bonding 35 2.3.2 Electron and hole flow 18 2.3.3 Doping 37 Activity 2.2 40 2.4 The pn junction 40 Activity 2.3 43 2.5 Summary 43 Self-evaluation 43 Answers 45 Unit 3 Diode theory 47 Outcomes AT 3.1 Introduetion 3.2 Forward biasing 48 Activity 3.4 5] 3.3 Reverse biasing 51 3.3.1 Reverse current 52 3.3.2 Reverse breakdown 0S Activity 3.2 53 3.4 The pn junction diode 53 Activity 3.3 56. 5 I dis el Activity 3.4 59 4.6__Practical diode model = SSC Activity 3.5 62 3.7 Full diode model and the real diode 62 3.7.1 Characteristic curves 3.7.2 Plotting the characteristic curve of a real diode 63 Urheberrechtlich geschiiztes Material3.1.3 Full diod Jel f I-biased 6 Activity 3.6 65 3.8 Temperature effects 65 Activity 3.7 66 39. Resistance 66 | 3.9.2 Average or ac resistance Activity 3.8 3.10 Summary | | 4.2.4 Selector guides W 4.2.5 Finding data on data sheets B Activity 4.1 79 43 Diode testing 79 4.3.1 Using a DMM to test a diode in the forward-biased 4.3.2 Using a DMM to test _a diode in the reverse-biased i Bi Activity 4.2 sl 44 Zener diodes £2 44.1 Zener diode data sheets 4.4... RG 44.2 Maximum ratings 86 4.4.4 Graphical data 89 * Activity 4.3 90 4.5 Light-emitting diodes (LEDs) 90 4.5.2 Biasing 91 4.5.3 Current-limiting resistor 92 5.4 LED lead identificati 93 Urheberrechtlich geschiiztes Material455 Multicoloured LEDs 4.5.6 Multi-segment displays 94 Activity 4.4 95 4.6 Summary 96 Self-evaluation 97 Answers 98 Unit 5 Diode applications 101 Outcomes 101 §.1__Introduction 102 5.2 Load line analysis 102 Activity 5.2 106 5.3 Dc input diode configurations 106 5.3.L Series diode configurations 106 5.3.2 Parallel and series-parallel diode configurations 2 Activity 5.2 113 5.4 Simple power supply circuits 113 5.4.3 Full-wave rectifiers \4||. DT & Pull-wave centre-tapped rectifiers 122 Bb Full-wave bridge rectifiers 126 Activity 5.3 130 5.5 Simple power supply filters — the capacitor filter 130 Activity 5.4 138 5.6 Clippers 138 5.6.1 Series clippers 138 5.6.2 Parallel clippers 140 Activity 5.5 142 5.7___Clampers 142 5.7.1 Positive clampers 143 5.7.2 Negative clampers 145 Activity 5.6 145 3.8 Summary 146 Selfeevaluation 4. Answers 153 Urheberrechtlich geschiiztes MaterialUnit 6 Transistor theory 159 Outcomes 159 6.1 Introduction 160 6.2 The Bipolar Junction Transistor (BJT) 160 6.2.1 Construction of a BJT 160 Activity 6.1 i6] 6.2.2 Basic operation of a BJT 161 Activity 6.2 164 6.3 Transistor current and voltage relationships 165 6.3.1 De alpha (a) 165 6.3.2 De beta (3) 165 Activity 6.3 168 6.4 Transistor characteristic curves Cid‘ Activity 6.4 174 6.5 Summary 174 Self-evaluation dN Answers ——SSS—“‘“‘CSSC*C*S*SCSCSCSC‘iCYL‘ TG Unit 7 Transistor characteristics 179 Outcomes 179 71__Introduction 180 72 Transistor datasheets = —“(—;C‘“—;*sC~C~CCCCC«~dSNS 7.2.1 Maximum ratings 182 2.2.2 OFF characteristics dN 1.2.3 ON characteristics 185 Activity 7.1 187 1.3___Limits of transistor operation 187 Activity 7.2 193 7.4 Testing a transistor 193 Activity 7.3 197 7.5 Summary 198 Self-evaluation 198 Answers 202 Unit 8 Transistor applications 203 Outcomes 203 &1 Introduction 204 8.2 DC biasing principles 204 8.2.1 DC load line 204 Urheberrechtlich geschiltztes Material8.2.2 Operating point 206 Activity 8.1 2u 8.3 Base bias 911 Activity 8.2 216 Activity 8.3 219 8.5 Voltage-divider bias 220 Activity 8.4 223 8.6 Collector-feedback bias 8 Activity 8.5 225 8.7 Design operations 226 Activity 8.6 232 8.8 Summary 232 Self-evaluation 24.4228 Answers 238 Unit 9 Field effect transistors 9... 2 Outcomes 0 8 9.1 Introduction 9.2 The Junction Field Effect Transistor (JFET) 244 Activity 9. 251 9.3 Biasing of the JEET 251 9.3.1 Fixed-bias circuit 253 9.3.3 Voltage-divider bias circuit 256 Activity 9.2 259 (MOSFET) 260 9.4.1 Depletion-type MOSFET (D-MOSFET) 260 9.4.2. Enhancement-type MOSFET (E-MOSFET) 264 Activity 9.3 266 9.5 Summary 267 Self-evaluation 20-8 Answers 272 Urheberrechtlich geschiiztes Material| Note to the student This book introduces the fundamental concepts of electronics to entry level tertiary students. It is designed as a one-semester course for students in the fields of electrical and electronic engineering. The language in the text is simple, conversational English. Difficult concepts and technical terms are explained throughout the book. This book has 9 units. Each unit starts with a list of outcomes or study objectives. These outcomes set out what you should be able to do at the end of the unit. The text is set out in such a way that you should be able to work through the book by yourselves. New concepts are explained and reinforced by giving examples with solutions to work through. Many figures are used throughout the text to aid understanding and clarify concepts. The mathematics in this course is thereby made clear and understandable. Your Grade 12 (Matric) Mathematics and Science knowledge will enable you to understand the concepts introduced in this book. The key to successful studying is to understand rather than memorise concepts, because each subsequent section will be based on an understanding of the previous work covered. Therefore it is important to work through the material in the order in which it is presented here. Once you understand something, it will also be much easier to remember it. Following each section of text, you will find an activity. These activities allow you to make sure that you have understood the work you have just covered. Do the activity only once you understand the entire section. The answers to the activities appear at the end of each unit. The summary at the end of each unit enables you to see at a glance what you should have learnt in the unit. The summary is followed by a section with self-evaluation exercises to assess your own progress. Answers to the self-evaluation exercises appear at the end of each unit. Once you understand the work covered in a unit and have successfully completed the self-evaluation exercises, you are ready to start the next unit.We have used four icons in this book: AH ae MAN IV Activity 1 U This is an ACTIVITY icon, When you see this icon you will know that it is time to DO something! The activities are active and enjoyable, and they help you to understand the subject. Feel free to do them with a friend or group of friends. The solutions to the activities are given at the end of each unit. This is a DEFINITION icon. Read the definitions carefully because the details are important. The TAKE NOTE icon appears alongside all the extremely important information. Mau Self-evaluation This is a self-evaluation icon. The self-evaluation exercises at the end of each unit enable you to assess your own progress.Instruments OUTCOMES After studying this unit, you should be able to: @ identify the following instruments: « digital multimeter « oscilloscope + function generator «dc power supply * breadboard @ set up and use the above instruments correctly.Introductory Electronics for Engineering aD Introduction In this unit you will learn about the instruments you will use in this electronics course and in almost every other course during your studies, and in your future career. _- You need To understand the basic operation of these instruments as | ‘this will give you the necessary confidence when using them ina practical situation, Multimeters are one of the most common instruments used by electrical engineers. They can usually measure at least three electrical quantities, namely amperes, volts and ohms. Two types of multimeters are available, namely analog and digital meters, but digital multimeters are the most widely used. 1.2.1 Analog multimeters Analog multimeters have a pointer which moves across a calibrated scale to indicate the value of the quantity being measured. You should be careful when using analog meters as the meter can be very easily damaged if it is bumped or if you use it incorrectly. Fig 1.1 shows a typical analog multimeter. Fig 1.1 A typical analog multimeterUnit 1 Instruments 1.2.2 Digital multimeters A digital multimeter (DMM) displays voltage (measured in volts), current (measured in amperes) and resistance (measured in ohms) measurements on a numerical display as numbers. Fig 1.2a-c shows various types of digital multimeters. (a) Hand-held DMM (b) Autorange hand-held DMM (c) Bench-type/hand-held DMM Fig 1.2 Various types of digital multimeters > Basic operation A digital multimeter operates very differently from the analog meter. The heart of the analog meter is the moving coil ammeter, while the DMM uses a digital voltmeter. The components used in a DMM are transistors, integrated circuits and the light-emitting diode (LED) or liquid-crystal display (LCD). Unlike analog multimeters, DMMs don’t have any moving parts, therefore they can withstand mechanical shock much better than the analog meters. The DMM works well when reading stable currents, but has difficulty in showing readings where the current changes continuously. DMM displays are updated every 0.5 seconds or so, and large variations in the input voltage might cause the display to change a lot, which makes it difficult to interpret. Some modern DMMs have overcome this problem by the addition of an analog bar graph which simulates the pointer of an analog meter. This kind of display is updated about 20 times per second, which results in a much faster response than the numerical display. b> Voltage measurements Voltage measurements are always done in parallel, as shown in fig 1.3a-c.4 Introductory Electronics for Engineering fle & (a) Measures voltage (b) Measures voltage (c) Measures voltage of cell E across Fi, across A, Fig 1.3 Voltage measurements are done in parallel The impedance of a DMM is usually much higher during voltage measurements than the impedance of the traditional analog meter. The impedance of the DMM usually stays the same for any range selected, and is in the order of 10 MQ. > Current measurements To measure current with a DMM the meter needs to be placed in series in the circuit. The DMM measures the voltage drop over its shunt resistor. RShut — 200mVv > To DMM circuitry Fig 1.4 A shunt resistor is used in a DMM to measure current b> Resistance measurements When you use a DMM to measure resistance, an internal current generator provides a known current to the resistor to be measured. This results in a voltage drop across the resistor. Fig 1.5 shows how the rest of the DMM circuitry uses this voltage drop. When the current is constant, the resistance of the resistor is directly related to the voltage drop generated over it. The resistance is displayed as a value in ohms.Unit 1 Instruments () Internal & eras va} To DMM circuitry Measured resistor |= Constant Fig 1.5 An internal current generator is used in a DMM to measure resistance 1.2.3 Other functions of multimeters More advanced DMMs can test transistors, measure capacitance, frequency, temperature, and even provide a square wave pulse. > Range selection The multimeter selector switch is usually divided into groups such as de V, ac V, de A, ac A, OHM (2) and all the other measurements the meter is capable of indicating. You can turn the selector switch to a specific value in a group. That value indicates the maximum allowable measurement that you can make. For the meter selection as shown in fig 1.6a, it is possible to measure from 0 to | 000 volt de. For fig 1.6b it is possible to measure from 0 to 400 mA with a fsd at 400 mA de. Full scale deflection (fsd) is when the display indicates the maximum reading for the selected range. Fig 1.6 Various meter range selections for dc voltage measurements It is always advisable to select the highest range for the quantity being measured and then turn the selector switch to a lower value for current or voltage measurements. This will prevent the meter from being damaged 5Introductory Electronics for Engineering by an incorrect selection. For example, if the meter is selected to measure 10 volts de and you apply 1 000 volts de, the pointer of an analog meter will shoot to the right of the meter and this might cause permanent damage to the instrument. DMMs are usually less fragile as far as voltage measurements are concerned when a very low range is incorrectly selected. The ideal range to choose for current and voltage measurements is the one that will be the closest to fsd, but it should be greater than the estimated value you are about to measure. You will see an over-range indication on the digital multimeter’s display when its input exceeds the selected range. Various techniques are used to indicate this: some will display 1999, or OL (for ‘overload’) and the readout usually starts to flash. If you want to measure 1.674 V with a DMM, it might display the values as shown in table 1.1 for various voltage range selections. Table 1.1 Range selection versus display readout for a DMM Input voltage (V) 1.674 Range selection (V) 1000 200 Readout display (V) Autorange digital multimeters are becoming increasingly more popular. You need only select the type of measurement that you would like to make, such as V dc, V ac, A de, A ac, 9, etc. and the meter will then automatically choose the best range during the measurement. The meters shown in fig 1.2b and c are autorange multimeters. b> Comparison Table 1.2 on the next page gives a summary of the differences between digital and analog multimeters.Unit 1 Instruments Table 1.2 Differences between digital and analog multimeters Accuracy Specification Digital Analog Loading effects (Voltage Insignificant effect on low Readings can be affected a measurements) resistance circuits. Could lot, especially on high have some effect on high resistance circuits. Extremely accurate for stable signals. resistance circuits. Less accurate, but it works better from } fsd to fsd for current and voltage measurements. Range selection Computer interface Manual or automatic Yes Manual No Changing signals Makes It very difficult to fead, but bar graph compensates a bit for this. Much easier to follow. Power requirements Reading errors Yes, but uses very little power. None Only for the ohmmeter. Can result from parallax Durability Very rugged Extra features. AY Activity 1.1 1 Measures frequency, Capacitance, temperature etc. Name the two types of multimeters. 2 How would you identify an analog meter? 3 Will the addition of a voltmeter cause the overall current flow of a circuit to increase or decrease? Give reasons for your answer. 4 What would the ideal magnitude of the meter impedance of an ammeter be? 5 How would you recognise a DMM? 6 Name five advantages that DMMs have when compared to analog meters. Sensitive to mechanical shockIntroductory Electronics for Engineering €.3) Oscilloscopes The human eye can see the physical components of an electronic circuit, but the oscilloscope helps you see what is going on inside an electronic circuit by giving a visual display on its screen (for example, a sine wave, a square wave, etc.) The oscilloscope can be used to measure voltage, time period/frequency, phase shift, rise or fall time, pulse duration, pulse delay time and repetition rate. An oscilloscope plots a two-dimensional graph with time on the x-axis and voltage on the y-axis, and therefore gives the exact wave shape of the measured signal. The proper name for an oscilloscope is cathode-ray oscilloscope because of the cathode-ray tube which forms the main component of a ‘scope’. 1.3.1 Basic operation Fig 1.7a is a photo of an oscilloscope, while fig 1.7b shows you the components found inside an oscilloscope. In the next section we will discuss the basic operation and function of the different parts of the oscilloscope in more detail. Fig 1.7a Front panel view of an oscilloscopeUnit 1 Instruments Line (50 or 6OHz} intemal ¥ Se External Vertical | trigger input input Trigger circultry Horizontal input Horizontal deflection plates Fig 1.7b Block diagram of a general-purpose oscilioscope including details of the cathode ray tube (CAT) 910 | Introductory Electronics for Engineering b Cathode ray tube (CRT) The cathode ray tube (CRT) is the component that gives a visual display of electrical waveforms. The heater inside the CRT (see fig 1.7b) will heat the cathode to such an extent that it starts emitting electrons from its end surface. The control grid has a negative charge with respect to the cathode and will control the number of electrons that will strike the phosphor coating of the screen. The brightness or intensity of the signal displayed will depend on the number of electrons that strike the phosphor coating. You can adjust the brightness on the front panel. Amode Aj, anode A; and the conductive coating (aquadag coating) have a more positive charge than the cathode, with A, the least positive of the three, and the conductive coating the most positive. The conductive coating is connected to an extra high tension (e.h.t) voltage source of a few thousand volts. The electrons that get through the control grid are accelerated towards the phosphor coating (screen) by the voltage of Aj, Aj and the conductive coating which becomes incrementally more positive. This happens because of the positive voltage which attracts the electrons that are negative in polarity. The electrostatic fields between A, and the control grid, and between A, and A», form an electrostatic lens that will focus the electron beam. The aim is to have a fine point by the time the electron beam strikes the phosphor coating. This is achieved by varying the voltages on Aj, also called the focus anode, and it can be controlled from the front panel. The phosphor coating of the screen inside the CRT gives off light when the electrons strike it. Without any voltage on the horizontal and vertical deflection plates, the electron beam strikes the phosphor screen in one place only (in the centre of the screen). This will cause a round dot to appear on the screen. A voltage applied to the horizontal deflection plates will cause the electron beam to be deflected towards the left or right (horizontally or x-axis). The electron beam with its negative polarity is attracted towards the horizontal deflection plate with the higher positive polarity. The vertical deflection plates work similarly, but the electron beam is deflected up or down (vertically or y-axis). The amount of deflection is directly related and linear to the amount of voltage applied to the deflection plates. b» The sweep generator The purpose of the sweep generator is to generate a voltage al the horizontal deflection plates. This will move the electronic beam horizontally across the screen (from left to right) at a constant speed (linear to time). Fig 1.8 shows a typical waveform generated by a sweepUnit 1 Instruments generator, as well as a graticule of an oscilloscope faceplate. The graticule is usually laid out in an 8 x 10 pattern of 1 cm squares. Each square represents 1 division. The minor divisions on the horizontal and vertical centre line represent 0.2 divisions. Centre graticule line Centre graticule line erat: Reret + Electron beam on ——+-+—-» 4+ Electron bearn on, ———+e— > v (time base related) ; : Time Fig 1.8 Waveform on horizontal plate in relation to the graticule of the facepiate The electron beam is deflected towards the extreme left of the screen at time zero, therefore it is not visible on the graticule. At this time, the voltage to the right-hand horizontal plate is at its lowest level. The electron beam is deflected towards the right of the screen as the voltage on the right-hand plate increases. It reaches the right-hand side of the screen when the sawtooth is at its highest voltage. During the flyback or retrace period, the electron beam is moved to the extreme left of the screen again. During this time, the voltage on the control grid is turned off, which makes the electron beam invisible. The whole process is then repeated to display the next screen, The horizontal position controller is used to set the start of the waveform horizontally to the left or right. The time to move the electron beam from the left to the right of the display can be changed on the horizontal time base. If the time base is set to | ys per division, the electron beam will move at a rate of | ys for 1112 Introductory Electronics for Engineering every division. It will take 10 ys for a beam to move from the left to the right on a graticule with 10 divisions. f <<” _ Be carefull The time per division >) (time/div) time base setting is only | ‘true when the oscilloscope's time | ' base is in the ealbrated (CAL) \ | mor > The vertical attenuator and vertical amplifier The signal to be viewed is applied to the volts/div attenuator via the vertical input jack. The vertical attenuator reduces the applied signal in such a way that the beam is vertically deflected in correlation with the volt/div attenuator setting. The valt/div setting will only be => true if the gain controller nee calibrated (CAL) mode. N The vertical amplifier enlarges or amplifies the signal from the vertical attenuator to a suitably high voltage as needed by the vertical deflection plates, > Triggering The trigger circuitry will ensure that the measured signal is stable on the CRT display. Fig 1.9a-c shows three displays of a sine wave, but the scope is not triggered. A wave is displayed on the CRT for every sweep generated by the sweep generator. You will find that the start position of the sine wave differs for every new sweep as shown in fig 1.9d. This causes the sine wave to move continuously horizontally on the display.Unit 1 Instruments Sweep 1 Sweep 2 Sweep 3 {a) Sine wave (b) Sine wave (c) Sine wave (0) Start at different starts at starts at Starts at position for each Position A position B position C sweep Fig 1.9 The scope is not triggered and a wave /s displayed at a different position for each sweep The ideal situation would be where the measured signal is displayed in the same position for every sweep of the sweep generator (assuming that the input signal stays the same). This will result in a stable, workable signal as shown in fig 1.10. Sweep 1 Sweep 2 Sweep 3 (a) Sine wave (b) B at same (c) Cat same (0) Each wave ‘starts at pointas A point as starts at same Position A AandB Position for each sweep Fig 1.710 The scope is triggered and a wave is displayed at the same position for each sweep The trigger circuitry determines when the ramp (rising) part of the sawtooth pulse from the sweep generator will start. When set to internal triggering, the trigger circuitry allows you to pick any point on the measured waveform to trigger on. The sweep generator will always start the horizontal sweep at this trigger point. The trigger point can be set for a specific voltage level and slope on a wave (see fig 1.11).