Understandable Electric Circuits: Key Concepts

454 Pages·2019·26.65 MB·English

by  Meizhong Wang

IETMATERIALS,CIRCUITS AND DEVICES SERIES 47
Understandable
Electric Circuits
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Understandable
Electric Circuits
Key concepts
2nd Edition
Meizhong Wang
The Institution of Engineering andTechnology
PublishedbyTheInstitutionofEngineeringandTechnology,London,UnitedKingdom
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†TheInstitutionofEngineeringandTechnology2019
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Contents
Abouttheauthor xv
Preface xvii
Acknowledgments xix
R Quantities andunits 1
R.1 International system of units (SI) 1
R.1.1 SI units and circuit quantities 1
R.1.2 Metric prefixes (SIprefixes) 2
R.1.3 Metric conversion 3
R.1.4 The unit factor method 4
R.2 Scientific notation 6
R.2.1 Write in scientific notation 6
R.3 Engineering notation 8
R.3.1 Write in engineering notation 8
Summary 10
Self-test 12
1 Basic conceptsof electric circuits 15
1.1 Introduction to electric circuits 15
1.1.1 Why studyelectric circuits? 15
1.1.2 Careers inelectrical, electronic, and computer engineering 16
1.1.3 Milestones of electric circuit theory 17
1.2 Electric circuitsand schematic diagrams 18
1.2.1 Basic electric circuits 18
1.2.2 Circuit schematics (diagrams) and symbols 20
1.3 Electric current 21
1.3.1 Current 21
1.3.2 1-ampere current 22
1.3.3 The direction of electric current 23
1.4 Electric voltage 24
1.4.1 Voltage/electromotive force 24
1.4.2 Potential difference/voltage 25
1.5 Resistanceand Ohm’slaw 27
1.5.1 Resistance/resistor 27
1.5.2 Factors affectingresistance 28
1.5.3 Conductance 31
vi Understandable electric circuits: key concepts, 2nd edition
1.5.4 Ohm’slaw 32
1.5.5 I–V characteristics of Ohm’slaw 34
1.6 Reference direction of voltage and current 35
1.6.1 Reference direction of current 35
1.6.2 Reference polarity of voltage 36
1.6.3 Mutually related reference polarity of current/voltage 37
Summary 38
Practice problems 40
2 Basic lawsof electric circuits 43
2.1 Power and energy 43
2.1.1 Work 43
2.1.2 Energy 44
2.1.3 Power 46
2.1.4 Electric power 46
2.1.5 The reference direction of power 48
2.2 Kirchhoff’s voltage law 50
2.2.1 Closed-loopcircuit 50
2.2.2 Kirchhoff’s voltage law (KVL) #1 51
2.2.3 Kirchhoff’s voltage law (KVL) #2 52
2.2.4 Experimental circuit of KVL 53
2.2.5 KVLextension 54
2.3 Kirchhoff’s current law 55
2.3.1 Kirchhoff’s current law (KCL) #1 55
2.3.2 Kirchhoff’s current law (KCL) #2 56
2.3.3 Physical property of KCL 58
2.3.4 Procedure to solve a complicated problem 59
2.3.5 Supernode 60
2.3.6 Some important circuit terminologies 62
2.4 Voltage source and current source 63
2.4.1 Ideal voltage source 63
2.4.2 Real voltage source 64
2.4.3 Ideal current source 66
2.4.4 Real current source 68
Summary 69
Practice problems 70
3 Series–parallel resistive circuits 75
3.1 Series resistive circuitsand voltage divider rule 76
3.1.1 Series resistive circuits 76
3.1.2 Series voltage and resistance 77
3.1.3 Series current and power 77
3.1.4 Anexample of a series circuit 78
3.1.5 Voltage divider rule (VDR) 79
3.1.6 Circuit ground 81
3.1.7 Voltage subscript notation 81
Contents vii
3.2 Parallel resistive circuits and current divider rule 82
3.2.1 Parallel resistive circuits 82
3.2.2 Parallel voltage and current 83
3.2.3 Parallel resistance and power 84
3.2.4 Anexample of a parallel circuit 85
3.2.5 Current divider rule (CDR) 86
3.3 Series–parallel resistive circuits 88
3.3.1 Equivalent resistance of a series–parallel circuit 88
3.3.2 Analysis of the series–parallel circuits 88
3.3.3 Currents and voltages of a series–parallel circuit 90
3.4 Wye (Y)and delta (D)configurations and their
equivalent conversions 91
3.4.1 Wye and delta configurations 91
3.4.2 Tee (T) and pi (p)configurations 92
3.4.3 Delta to wye conversion(D!Y) 93
3.4.4 Wye todelta conversion(Y!D), RY,and RD 94
3.4.5 Anexample of wye and delta conversion 95
3.4.6 UsingD! Yconversion to simplify bridge circuits 96
3.4.7 Balanced bridge 97
3.4.8 Measure unknownresistorsusingthe balanced bridge 98
Summary 99
Practice problems 101
4 Methodsof DCcircuit analysis 109
4.1 Voltage source, current source, and their equivalent conversions 109
4.1.1 Source equivalent conversion 109
4.1.2 Verification of source conversion 111
4.1.3 Source conversion examples 111
4.1.4 Voltage sources in series 113
4.1.5 Voltage sources in parallel 114
4.1.6 Current sources in parallel 115
4.1.7 Current sources in series 115
4.2 Branch current analysis 116
4.2.1 Branch current analysis 116
4.2.2 Procedure for applying the branch current analysis 117
4.2.3 Branch current analysisexamples 118
4.3 Mesh analysis 121
4.3.1 Mesh current analysis 121
4.3.2 Procedure for applying the mesh current analysis 122
4.3.3 Mesh current analysis examples 122
4.4 Nodal voltage analysis 125
4.4.1 Procedure for applying the node voltage analysis 125
4.4.2 Node voltage analysis examples 126
4.4.3 Node voltage analysis vs.mesh current analysis 130
Summary 130
Practice problems 132
viii Understandable electric circuits: key concepts, 2ndedition
5 The network theorems 137
Introduction to the network theorems 137
5.1 Superposition theorem 138
5.1.1 Steps toapply the superposition theorem 138
5.1.2 Superposition examples 139
5.2 Thevenin’s and Norton’s theorems 143
5.2.1 Introduction to Thevenin’sand Norton’s theorems 143
5.2.2 Thevenin and Norton equivalentcircuits 143
5.2.3 Equivalent resistance and voltage/current 144
5.2.4 Procedure for applying the Thevenin’s and
Norton’s theorems 145
5.2.5 Thevenin/Norton equivalent example 146
5.2.6 Viewpointsof Thevenin’s and Norton’s
equivalent circuits 148
5.2.7 Norton’s theorem examples 153
5.3 Maximumpower transfer 157
5.3.1 Maximumpower transfer theorem 157
5.3.2 Applicationsof maximum power transfer 158
5.3.3 Proof of maximum power transfer theorem 159
5.4 Millman’s and substitution theorems 160
5.4.1 Millman’stheorem 160
5.4.2 Millman’stheorem example 162
5.4.3 Substitutiontheorem 163
5.4.4 Substitutiontheorem example 164
Summary 165
Practice problems 167
6 Capacitors andinductors 171
6.1 Capacitors 172
6.1.1 Three basic circuit components 172
6.1.2 Capacitors 172
6.1.3 Charging a capacitor 173
6.1.4 Howdoes a capacitor store energy? 175
6.1.5 Discharging a capacitor 175
6.1.6 Capacitance 176
6.1.7 Calculating capacitance 177
6.1.8 Factors affectingcapacitance 178
6.1.9 Leakage current and breakdown voltage 180
6.1.10 Relationship between the v and i of a capacitor 180
6.1.11 Ohm’slaw for a capacitor 181
6.1.12 Energy stored by a capacitor 182
6.2 Capacitors inseries and parallel 183
6.2.1 Total or equivalent capacitance 183
6.2.2 Capacitors in series 185
6.2.3 Capacitors in parallel 186
Contents ix
6.2.4 Physical properties of parallel C 187
eq
6.2.5 Capacitors inseries–parallel 188
6.3 Inductors 189
6.3.1 Electromagnetism induction 189
6.3.2 Faraday’s law 190
6.3.3 Lenz’s law 191
6.3.4 Inductors 192
6.3.5 Self-inductance 192
6.3.6 Ohm’slaw foran inductor 193
6.3.7 Factors affectinginductance 194
6.3.8 Energy stored in an inductor 195
6.3.9 Calculating the energy stored in an inductor 196
6.3.10 Winding resistor of an inductor 197
6.4 Inductors in series and parallel 198
6.4.1 Series and parallel inductors 198
6.4.2 Inductors in series–parallel 200
Summary 201
Practice problems 202
7 Transientanalysis of circuits 205
7.1 The first-order circuit and its transient response 206
7.1.1 First-order circuit 206
7.1.2 Transient and steady state 206
7.1.3 Step response 207
7.1.4 Source-free and unit-step response 208
7.1.5 The initial condition of the dynamic circuit 209
7.2 The step responseof an RCcircuit 210
7.2.1 The charging process of an RC circuit 210
7.2.2 Quantity analysis of the RCcharging process 212
7.2.3 Charging equationsfor an RCcircuit 213
7.2.4 Example with RCcircuit 214
7.3 The source-free response of the RCcircuit 215
7.3.1 The discharging process of the RCcircuit 215
7.3.2 Quantity analysis of the RCdischarging process 216
7.3.3 RCtime constant 218
7.3.4 The RCtime constant and charging/discharging 219
7.3.5 Different time constants for charging/discharging 220
7.3.6 Discharging process examples 221
7.4 The step responseof an RL circuit 222
7.4.1 RL circuit 222
7.4.2 Energy-storingprocess of the RL circuit 223
7.4.3 Quantity analysis of the RL energy-storing process 224
7.5 Source-free responseof an RL circuit 226
7.5.1 Energy-releasingprocess of an RL circuit 226
7.5.2 Quantity analysis of the RL energy-releasing process 227