Industrial Electronic Circuits Laboratory Manual (Synthesis Lectures on Electrical Engineering)

Synthesis Lectures on Electrical Engineering
Farzin Asadi
Industrial
ElectronicCircuits
Laboratory
Manual

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Synthesis Lectures on Electrical
Engineering

This series of short books covers a broad spectrum of titles of interest in electrical
engineering that may not specifically fit within another series. Books will focus on
fundamentals, methods, and advances of interest to electrical and electronic engineers.

Farzin Asadi
Industrial Electronic Circuits
Laboratory Manual

Farzin Asadi
Department of Electrical and Electronics
Engineering
Maltepe University
Istanbul, Türkiye
Department of Electrical and Electronics
Engineering
Beykent University
Istanbul, Türkiye
ISSN 1559-811X ISSN 1559-8128 (electronic)
Synthesis Lectures on Electrical Engineering
ISBN 978-3-031-50772-4 ISBN 978-3-031-50773-1 (eBook)
https://doi.org/10.1007/978-3-031-50773-1
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature
Switzerland AG 2024
This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole
or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,
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hereafter developed.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does
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The publisher, the authors, and the editors are safe to assume that the advice and information in this book are
believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give
a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that
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The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland
Paper in this product is recyclable.

Preface
This is a book for a lab course meant to accompany, or follow, any standard course in
industrial/power electronics. This book has the following objectives:
1. To support, verify, and supplement the theory; to show the relations and differences
between theory and practice.
2. To teach measurement techniques.
3. To convince students that what they are taught in their lecture classes is real and useful.
4. To help make students tinkerers and make them used to asking “what if” questions.
This book contains 50 experiments, which help the reader to explore the concepts studied
in the classroom. It is assumed that the reader is familiar with the working principles of
circuits. The references given at the end of chapters helps you to refresh your theoretical
knowledge. Here is a brief summary of chapters and appendixes:
Chapter 1 studies the most commonly used measurement devices that are used in the
laboratory.
Chapter 2 studies the most commonly used switches (i.e., relay, BJT, MOSFET,
temperature, and reed switches).
Chapter 3 studies the thyristor and triacs.
Chapter 4 studies the different types of power supply circuits.
Chapter 5 studies the DC-DC converter circuits.
Chapter 6 studies the different types of filter and comparator circuits.
Chapter 7 studies the speed and direction control of DC motors.
Chapter 8 studies the delay generator circuits.
Appendix shows how to draw different types of graphs with MATLAB®.
I hope that this book will be useful to the readers, and I welcome comments on the
book.
Istanbul, Türkiye Farzin Asadi
v

Contents
1 Commonly Used Laboratory Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Digital Multi Meter (DMM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Function Generator (Signal Generator) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Oscilloscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.6 Breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.7 Measurement with Cell Phone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.8 Conventions Used in This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
References for Further Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2 Different Types of Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Relay Test Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4 Control of Relay with BJT Transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5 Control of Relay with MOSFET Transistor . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.6 Optocoupler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.7 Control of Relay with an Optocoupler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.8 Darlington Pair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.9 MOSFET as Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.10 Control of Load Current with Optocoupler and MOSFET Transistor . . . 30
2.11 Temperature Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.12 Reed Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.13 Infrared Transmitter and Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
vii

viii Contents
3 Thyristors and Triacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.2 Relaxation Oscillator with UJT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 Thyristor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.4 Thyristor Turn Off Methods in DC Circuits . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5 Diac . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.6 Pulse Generation with Diacs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.7 Dimmer Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.8 Controlled Rectifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4 Power Supply Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2 Half Wave Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3 Full Wave Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4 Symmetric Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.5 Voltage Regulator ICs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.6 Regulated Power Supply with High Output Current and Short
Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.7 Regulator with Adjustable Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.8 Obtaining a High Regulated Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . 61
4.9 Current Source Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.10 LM317 Adjustable Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.11 Overload Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.12 Over Voltage Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.13 Over Temperature Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.14 Voltage Multiplier Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
4.15 Simple Inverter Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5 DC-DC Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.2 Boost Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.3 Buck Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.4 Voltage-Inverting Converter with TL7660 IC . . . . . . . . . . . . . . . . . . . . . . . 79
5.5 Voltage-Inverting Converter with MC33063 IC . . . . . . . . . . . . . . . . . . . . . . 79
5.6 Voltage Inverting Converter with 555 IC . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.7 Voltage Doubler Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Contents ix
6 Filter and Comparator Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.2 Simple Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.3 Window Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.4 Low Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
6.5 High Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.6 Band Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7 Control of DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.2 Direction of Rotation Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.3 DC Motor Speed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.4 Control the Direction of Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.5 Full-Bridge Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
7.6 Speed Control of Universal Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7.7 Stepper Motor and BLDC Motor Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
8 Delay Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
8.2 Delay Circuit with Transistor (Normally on Circuit) . . . . . . . . . . . . . . . . . 111
8.3 Delay Circuit with Transistor (Normally Off Circuit) . . . . . . . . . . . . . . . . 112
8.4 Delay Circuit with 555 IC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
8.5 555 Timer IC Based Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Drawing Graphs with MATLAB® . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

1
Commonly Used Laboratory Equipment
1.1 Introduction
This chapter studies the most commonly used devices in the laboratory. Measurement
devices that are used in different laboratories are made by different companies. Working
with each device has its own details. Therefore, you are encouraged to read the user
manual of devices that you will use during the experiments. Another good reference is
your laboratory instructor. Studying the Ref. [1] is recommended as well.
1.2 Digital Multi Meter (DMM)
Digital multimeters are measuring instruments that can measure quantities such as voltage,
current, and resistance. Measured values are shown on a digital display, allowing them to
be read easily and directly, even by first-time users.
Study the user manual of the DMM that you will use in the experiments. Ensure that
you are able to do the followings:
(a) Measurement of resistance.
(b) Measurement of AC/DC voltages.
(c) Measurement of AC/DC currents in the range of Amps.
(d) Measurement of AC/DC currents in the range of milli/micro Amps.
Ask your laboratory instructor to make an explanation to you if you are not able to do
one or more of the above tasks.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
F. Asadi, Industrial Electronic Circuits Laboratory Manual, Synthesis Lectures on
Electrical Engineering, https://doi.org/10.1007/978-3-031-50773-1_1
1

2 1 Commonly Used Laboratory Equipment
1.3 Function Generator (Signal Generator)
A function generator (sometime is called signal generator) is used to generate different
types of electrical waveforms over a wide range of frequencies. Some of the most common
waveforms produced by the function generator are the sine wave, square wave, triangular
wave and saw tooth shapes.
The FG’s are divided into two groups: Analog FG’s and Direct Digital Synthesis (DDS)
FG’s. As the name suggests, the analog FG’s, uses the analog circuits in order to produce
the output waveform. DDS FG’s use digital circuits (i.e. a microprocessor) in order to
produce the output waveforms. Accuracy of DDS signal generators is better than analog
signal generators.
Beside the standard waveforms (i.e. sinusoidal, square, triangular and saw tooth), some
DDS FG’s are able to produce arbitrary waveforms. These type of FG’s are called Arbi-
trary Waveform Generator (AWG). They have software which permits you to draw the
waveform that you want. After drawing the waveform in the software environment, the
hardware of AWG produces the waveform for you.
Output of function generator is connected to the circuit under test with the aid of a
cable (Fig. 1.1). Black wire is connected to the ground of the signal generator as shown in
Fig. 1.2. R1 shows the output resistance of the signal generator which is generally 50 Ω.
Fig.1.1 Signal generator cable

1.4 Oscilloscope 3
Fig.1.2 Simple model for signal generator
Study the user manual of the function generator that you will use in the experiments.
Ensure that you are able to do the followings:
(a) Generation of a sinusoidal signal with amplitude of 5 V and frequency of 50 Hz, i.e.,
v(t) = 5 × sin(2π × 50 × t) V.
(b) Generation of a sinusoidal signal with amplitude of 5 V, frequency of 50 Hz and
average value of 3 V, i.e., v(t) = 3 + 5 × sin(2π × 50 × t) V.
(c) Generation of a sinusoidal signal with peak value of 50 mV, i.e., v(t) = 0.05 ×
sin(2π × 50 × t) V.
(d) Generation of a triangular wave with frequency of 50 Hz and peak value of 5 V
(Fig. 1.3).
(e) Generation of a pulse with frequency of 50 Hz and duty cycle of 25% (Fig. 1.4).
1.4 Oscilloscope
An oscilloscope is an instrument that graphically displays electrical signals and shows
how those signals change over time. Scientists, engineers, physicists, repair technicians
and educators use oscilloscopes to see signals change over time. These days generally
digital scopes are used in laboratory.

Fig.1.3 Sample triangular wave
Fig.1.4 Sample pulse
Study the user manual of the oscilloscope that you will use in the experiments. Ensure
that you are able to do the followings:
(a) Measurement of peak value of a signal.
(b) Measurement of period and frequency of a periodic signal.
(c) Use the cursors to read voltage or time difference between two points.
(d) Observing two waveforms simultaneously.
(e) Measurement of phase difference between two waveforms. Remember that you can
measure the phase difference between two waveform easily with the aid of Δϕ =
Δt
T × 360◦ formula (Fig. 1.5).
(f) Explain the difference between AC and DC coupling.
(g) Explain the functionality of X1/X10 switch on the probe.

1.5 Power Supply 5
Fig.1.5 Measurement of phase difference. B leads A by Δϕ = Δt
T × 360◦
1.5 Power Supply
All the circuits require an energy source in order to work. The power supply (PS) is
responsible for providing the required energy for the circuit. The power supply takes the
AC electric energy from the grid and converts it into a DC voltage. Generally, they provide
the voltages in the 0–30 V range. Generally, the output current could be up to 3 A. The
outputs of a PS are called a “Channel”. So, when we speak about a 3 channel PS, we
mean a PS with three outputs. Generally, the outputs are variable and the user could set
them to the desired value he/she wants. Generally, PS’s have one regulated output with
voltage of 5 V. This output is used to supply digital circuits. Remember that traditional
digital circuits work with 5 V (However this voltage decreased to 3.3 V and even 1.1 V
these days!). So, it is a good idea to use this fixed 5 V when you work with traditional
digital circuits. You can connect a digital circuit to variable outputs of a PS. However,
if you increase the voltage of that variable channel by mistake, then your circuit may be
damaged. So, always use this fixed 5 V when you are working with traditional digital
circuits.

Study the user manual of the power supply that you will use in the experiments. Ensure
that you are able to do the followings:
(a) Generation of 12 V with maximum output current of 0.5 A.
(b) Generation of 12 V with maximum output current of 5 A (Use parallel mode).
(c) Generation of 40 V with maximum output current of 1 A (Use series mode).
(d) Generation of a symmetric voltage for instance +12 and −12 V with maximum output
current of 0.5 A.
1.6 Breadboard
A breadboard is used to build and test circuits quickly. The breadboard has many holes
into which circuit components like ICs and resistors can be inserted. A typical breadboard
is shown in Fig. 1.6.
The breadboard has strips of metal which run underneath the board and connect the
holes on the top of the board. The metal strips are laid out as shown below. Note that the
Fig.1.6 Bead board

1.6 Breadboard 7
top and bottom rows of holes are connected horizontally while the remaining holes are
connected vertically (Figs. 1.7 and 1.8).
Let’s study an example. Assume that want to make the circuit shown in Fig. 1.9 on
breadboard.
Let’s start from the left side. Put the resistor R1 on the breadboard (Fig. 1.10).
Fig.1.7 Connections of breadboard
Fig.1.8 Inside of a breadboard

Fig.1.9 Sample circuit
Fig.1.10 Resistor R1 is added

1.7 Measurement with Cell Phone 9
Put the resistor R2 (Fig. 1.11).
Put the capacitor C1 (Fig. 1.12).
Put the resistor R3 (Fig. 1.13).
Connect the resistor R1 to the positive voltage rail and R2 and R3 to the negative
voltage rail (Fig. 1.14).
Connect the power supply to the breadboard (Fig. 1.15).
1.7 Measurement with Cell Phone
You can convert your cell phone, tablet or even your smart watch into a digital multimeter,
digital storage oscilloscope (DSO) or a logger with the aid of Pokit meter (Figs. 1.16 and
1.17) or Pokit pro (Fig. 1.18). More information can be found on https://www.pokitinno
vations.com/.

Fig.1.12 Capacitor C1 is added

1.7 Measurement with Cell Phone 11
Fig.1.14 Power supply connection are made
Fig.1.15 Voltage source is added to the circuit

Fig.1.16 Pokit meter
Fig.1.17 Pokit meter

1.8 Conventions Used in This Book 13
Fig.1.18 Pokit pro
1.8 Conventions Used in This Book
In this book the symbols shown in Fig. 1.19 are used to show pass of two wires over each
other without any connection. Figure 1.20 shows that two wires are connected to each
other.
Electrolytic capacitors are shown with the symbol shown in Fig. 1.21. Capacitance of
the capacitor is shown behind the symbol. Polarity of the capacitor is shown in Fig. 1.22.
Fig.1.19 There is no contact between w1 and w2
Fig.1.20 There is a contact
between w1 and w2

Fig.1.21 Symbol used for
electrolytic capacitors
Fig.1.22 Polarity of
electrolytic capacitor terminals
The terminal that is not hatched must be connected to the higher potential. The hatched
terminal must be connected to the lower potential.
References for Further Study
1. Asadi F., Eguchi K., Electronic Measurement: A Practical Approach, Springer, 2021.
2. Asadi F., Power Electronics Circuit Analysis with PSIM®, De Gruyter, 2021. DOI: https://doi.
org/10.1515/9783110740653
3. Asadi F., Simulation of Power Electronics Circuits with MATLAB®/Simulink®: Design, Ana-
lyze, and Prototype Power Electronics, Apress, 2022. DOI: https://doi.org/10.1007/978-1-4842-
8220-5
4. Asadi F., Eguchi K., Simulation of Power Electronics Converters Using PLECS®, Academic
Press, 2019. DOI: https://doi.org/10.1016/C2018-0-02253-7
5. Asadi F., Analog Electronic Circuits Laboratory Manual, Springer, 2023. DOI: https://doi.org/
10.1007/978-3-031-25122-1
6. Asadi F., Electric Circuits Laboratory Manual, Springer, 2023. DOI: https://doi.org/10.1007/
978-3-031-24552-7
7. Asadi F., Essential Circuit Analysis using NI Multisim™ and MATLAB®, Springer, 2022. DOI:
https://doi.org/10.1007/978-3-030-89850-2

References for Further Study 15
8. Asadi F., Essential Circuit Analysis Using Proteus®, Springer, 2022. DOI: https://doi.org/10.
1007/978-981-19-4353-9
9. Asadi F., Essential Circuit Analysis using LTspice®, Springer, 2022. DOI: https://doi.org/10.
1007/978-3-031-09853-6
10. Asadi F., Electric and Electronic Circuit Simulation using TINA-TI®, River Publishers, 2022.
DOI: https://doi.org/10.13052/rp-9788770226851
11. Asadi F., Electric Circuit Analysis with EasyEDA, Springer, 2022. DOI: https://doi.org/10.1007/
978-3-031-00292-2

2
Different Types of Switches
2.1 Introduction
In electrical engineering, a switch is an electrical component that can disconnect or
connect the conducting path in an electrical circuit, interrupting the electric current or
diverting it from one conductor to another. Switches play an important role in industrial
electronics. Important types of switches are studied in this chapter.
2.2 Relay
Relay is an electromechanical switch. You can use a relatively small current to control a
large current. Relays are thousand and million times slower than electronic switches like
BJT and MOSFET’s. Relays are bidirectional switches. Therefore, you can use them in
both AC and DC circuits.
Each relay has a coil. The current passes through the coil makes an electromagnet.
The electromagnet closes or opens the relay’s contacts.
Important types of relays are shown in Fig. 2.1. In Fig. 2.1, SPST, SPDT, DPST and
DPDT stands for Single Pole Single Through, Single Pole Double Through, Double Pole
Single Through and Double Pole Double Through, respectively.
Each relay works with a certain voltage. The required operating voltage for the coil and
current allowed to pass through relay contacts is printed on the relay case. For instance,
for the relay shown in Fig. 2.2, the operating voltage for the coil is 12 V. The contacts of
this relay can handle 250 VAC/10 A or 30 VDC/10 A load. Why the allowed DC voltage
is much smaller than the allowed AC voltage?
17

18 2 Different Types of Switches
Fig.2.1 Important types of
relays
2.3 Relay Test Circuit
Circuit shown in Fig. 2.3 is a simple circuit to test a SPST relay. VDC equals to the
nominal voltage of the relay coil. AC sinusoidal signal is large enough to turn on the
light bulb. When you press the push button, the coil is energized and the lamp turns on.
Test circuit for a SPDT relay is shown in Fig. 2.4. When the push button is not pressed,
L1 is on and L2 is off. When you press the push button, L1 turns off and L2 turns on.
VDC equals to the relay’s nominal coil voltage. AC sinusoidal signal is large enough to
turn on the light bulb.
Assume that the available DC voltage is bigger than the nominal voltage of the coil.
You can use the circuit shown in Fig. 2.5 in this case.
Let’s calculate the value of required resistor R1 in Fig. 2.5. When the push button
is pressed, the nominal current must pass through the coil. So, Inom =
V DC−Vrelay
R1
⇒
R1 =
V DC−Vrelay
Inom
. For instance, assume that we have a 12 V relay with coil resistance
of 400 Ω. In this case nominal current is Inom = 12
400 = 30mA. When VDC = 15 V,
R1 =
V DC−Vrelay
Inom
= 15−12
30 = 0.1 kΩ = 100 Ω (Fig. 2.6).

2.3 Relay Test Circuit 19
Fig.2.2 A sample relay
Fig.2.3 Simple test circuit for SPST relay
Make the circuits shown in Fig. 2.6 and ensure that it works as expected. Calculate the
value of resistor R1 based on the relay that you used.

Fig.2.4 Simple test circuit for SPDT relay
Fig.2.5 Using a series resistor to set the relay voltage
2.4 Control of Relay with BJT Transistor
You can use the circuit shown in Fig. 2.7 to control a relay with a microcontroller. The
microcontroller pin generates 0 and 5 V (or 0 and 3.3 V). When the microcontroller
pin is high, the transistor is in the saturation state and the relay coil is energized. When

2.4 Control of Relay with BJT Transistor 21
Fig.2.6 Supplying a 12 V relay from a 15 V supply
microcontroller pin is 0 V, the transistor is in the cut-off state and coil is not energized
and the pole is connected to normally close (NC) pin.
Let’s design the circuit shown in Fig. 2.7. Assume that given relay is a 12 V relay
with nominal current of 30 mA. This means that resistance of the coil is 400 Ω. TIP
41 is a good option for Q1. Let’s take the current equal to 40 (βmin = 40). Therefore,
Fig.2.7 Control of a relay with a BJT transistor

IB ≥ Inom
β = 30
mA40 = 750 μA. IB = 5−0.7
R1
≥ 750 μA ⇒ R1 ≤ 5.73 kΩ. Note that
IB shows the base current of Q1. Vrelay equals to 12 V since selected relay requires 12
V. Diode D1 protect the transistor Q1 against the voltage induced in the relay coil during
the turn off time.
Design the circuit shown in Fig. 2.7 based on relay available in your lab and test it.
Use 0 and 5 V to test the circuit.
2.5 Control of Relay with MOSFET Transistor
You can use a MOSFET to control a relay as well. The circuit shown in Fig. 2.8 can be
used for this purpose. Diode D1 protects the MOSFET against the induced voltage of relay
coil. The microcontroller pin generates 0 and 5 V. When microcontroller generates 0 V, no
current passes through the relay coil and the pole is connected to normally close terminal.
When it generates 5 V, the coil is energized and connects the pole to normally open
terminal. According to IRFZ 44 N datasheet, maximum of gate-source threshold voltage
is 4 V. Therefore, 5 V can turn on the transistor since 5; V > max(V GS,threshold) = 4 V.
Fig.2.8 Control of a relay with a MOSFET transistor

2.6 Optocoupler 23
Fig.2.9 A sample circuit to turn on/off a 12 V relay
Make the circuit shown in Fig. 2.9 and ensure it works properly.
You can use NTD3055L170 MOSFET if your microcontroller generates 0 and 3.3 V.
Maximum gate-source threshold voltage for NTD3055L170 equals to 2 V. Therefore,
3.3 V can turn on the NTD3055L170.
2.6 Optocoupler
Optocoupler (Opto-isolator) is device that transfer electrical signals between two isolates
circuits with the aid of light. Generally, one of the isolated circuits works with a high
voltage. We want to isolate this high voltage from the other circuit, which works with a
low voltage and contains sensitive components like IC’s and transistors.

Fig.2.10 Simple test circuit for optocoupler
Let’s see how an optocoupler works. Prepare the circuit shown in Fig. 2.10. When the
LED is not energized, the collector-emitter connection behaves like an open circuit and
collector voltage equals to VCC which in Fig. 2.10 is 12 V. When the LED is energized,
the collector-emitter behaves like short circuit and collector voltage is a small value.
Apply the 0 and +5 V to the resistor R1 (Figs. 2.11 and 2.12) and measure the collector
voltage. Does it work as expected? Measure the voltage drop across the LED in Fig. 2.12
as well.
Search the internet and see what an optocounter is and how it works.

2.7 Control of Relay with an Optocoupler 25
Fig.2.11 0 V is applied to resistor R1
2.7 Control of Relay with an Optocoupler
The optocoupler can be used in control of relays as well. The circuit shown in Fig. 2.13
can be used to turn on/off a light bulb. When control signal is +5 V the LED turns on
and the phototransistor energizes the relay coil. When control signal is 0 V the LED is
reverse biased and no current passes through the phototransistor. In this case the relay
coil is not energized and the contacts are in the NC state.
You can use the circuit shown in Fig. 2.14 if your relay requires more current than the
maximum current of the optocoupler. When the LED is forward biased (control signal =
+5 V), the phototransistor turns on and cause the Q1 to enter into the cut-off mode. The
relay coil is not energized in this case and the relay contacts are in the NC state. When the
LED is reverse biased (control signal = 0 V), the photo transistor is in the cut-off mode
and Q1 is in the saturation mode. When Q1 is saturated, the relay’s coil is energized and
the relay’s contacts are in the NO mode.

Fig.2.12 +5 V is applied to resistor R1
Make the circuits shown in Figs. 2.13 and 2.14 and ensure that they work as expected.
Measure the voltage of different nodes for different values of control signal. Compare the
measurements with hand analysis results.
2.8 Darlington Pair
The Darlington transistor named after its inventor, Sidney Darlington. Basic Darlington
transistor configurations are shown in Fig. 2.15. Providing a high current gain is the
advantage of the Darlington pair. Equivalent current gain for Darlington pair is around
β1×β2 where β1 and β2 shows the current gain of the first and second transistor. Note
that we have two base emitter junction; therefore, a voltage drop of 1.4 V is expected.
ULN2033 is a famous Darlington array.

2.8 Darlington Pair 27
Fig.2.13 Control of a relay with optocoupler
Fig.2.14 Sample test circuit to control a 12 V relay

Fig.2.15 Darlington pair
Let’s get started. Make the circuit shown in Fig. 2.16 (Use a 10 Ω, 10 W resistor as
load). Set the VB equal to 0 V and start to increase it slightly. Pay attention to the value
shown by the voltmeter. What is the minimum value shown by the voltmeter?
Measure the circuit currents (base of Q1, collector of Q1, emitter of Q1, collector of
Q2 and emitter of Q2) for VB = 10 V. Measure the voltage of base Q1 as well. Use the
measurements to calculate the equivalent current gain (βeq =
IC1 +IC2
IB1
).
BDX 33 contains two transistors connected in Darlington configuration. You can use
this device instead of using two discrete transistors.
2.9 MOSFET as Switch
MOSFET’s can be used as switches to connect or disconnect load current. The MOSFET
turns on when you give a gate-source voltage which is bigger than the threshold voltage.
Let’s get started. Make the circuit shown in Fig. 2.17. Increase the VG from 0 to 5 V
with 0.5 steps. Pay attention to the collector voltage. Find the minimum value that turns
on the MOSFET.

2.9 MOSFET as Switch 29
Fig.2.16 Control of a load with a Darlington pair
You can control the load power with the aid of pulses applied to the gate terminal of
the MOSFET. Make the circuit shown in Fig. 2.18 and apply pulses with different duty
cycles to the gate terminal (Fig. 2.19). Observe the output (drain voltage) and input (gate
voltage) simultaneously. What is the relationship between input and output?
Use the oscilloscope to measure the RMS of load voltage. Use the RMS value to find
the power dissipated in the load.
You can use the circuit shown in Fig. 2.20 to control the speed of small DC motors.
The diode protects the transistor against the high voltages generated by armature winding.
Make the circuit shown in Fig. 2.20 and apply a gate pulse with duty cycle of 20% and
frequency of 500 Hz (Fig. 2.21). Increase the duty cycle from 20% up to 80% with 10%
steps and observe the change of DC motor speed.
You can use the TL 494 to control the speed of small DC motors as well. TL 494
generates the required pulses for you and eliminates the need for a signal generator.

Fig.2.17 Measurement of threshold voltage of the MOSFET
2.10 Control of Load Current with Optocoupler and MOSFET
Transistor
The circuit shown in Fig. 2.22 can be used to control a load current. Vload is the voltage
required for the load. When control signal is +5 V, the LED is forward biased and the
phototransistor is in saturation mode. Q1 is reverse biased and Q2 charges the gate-source
capacitor of the MOSFET. This turns on the MOSFET and load current starts to flow.
Diode D1 protects the MOSFET against the inductive loads.
When control signal is 0 V, the LED is reverse biased and the phototransistor is cut-off
mode. Q1 conducts and cause Q3 to discharge the gate-source capacitor of the MOSFET.
This turns off the MOSFET and load current stops.

2.10 Control of Load Current with Optocoupler and MOSFET Transistor 31
Fig.2.18 Control of a load with a MOSFET
Fig.2.19 Frequency of these pulses is 10 kHz

Fig.2.20 Speed control of a DC motor with a MOSFET
Fig.2.21 Gate pulses
Make the circuit shown in Fig. 2.22. Use a 10 Ω resistor as load (Vload = 12 V). Give
different control signals to the circuit and observe its behavior. Measure the DC voltage
of different nodes and compare them with your hand analysis results.

2.11 Temperature Switch 33
Fig.2.22 Control of a load with an optocoupler and MOSFET
2.11 Temperature Switch
Temperature switches (thermostats) are a type of switches that change state based on the
temperature. Temperature switches are divided into two groups:
(A) Contact opens when temperature rises to set point (Normally Closed),
(B) Contact closes when temperature rises to set point (Normally Open).
Two type of temperature switches are shown in Figs. 2.23 and 2.24.
Let’s get started. Make the circuit shown in Fig. 2.25 with the temperature switch
you have in the lab. Use a soldering iron to increase the temperature of the temperature
Fig.2.23 Sample temperature switches

Fig.2.24 Sample temperature switch
switch and see what happens. Then remove the soldering iron and permit the sensor to
start cooling down. What happens in this case?
2.12 Reed Switch
The reed switch is an electromechanical switch operated by an applied magnetic field. It
can be used to turn on/off a device based on presence/absence of a magnetic field. When
magnetic field exists, the reed switch acts as short circuit. When magnetic field does not
exist, it act as open circuit.
Let’s get started. Make the circuit shown in Fig. 2.26. Bring a magnet close to the reed
switch and observe what happens.
2.13 Infrared Transmitter and Receiver
You can use infrared transmitter and receiver (Figs. 2.27 and 2.28) to turn on or off a
devices. For instance, hand dryers use these type of sensors in order to detect whether
user hand is put in front of the device. Infrared transmitter and receivers are Arduino
compatible. Therefore, you can use an Arduino board to read them [1].

2.13 Infrared Transmitter and Receiver 35
Fig.2.25 Test circuit for temperature switch
Fig.2.26 Test circuit for reed switch

Fig.2.27 A sample of infrared transmitter and receiver
Fig.2.28 A sample of infrared transmitter and receiver
1. Asadi F., Essential of Arduino Boards Programming: Step-by-Step Guide to Master Arduino
Boards Hardware and Software, Apress, 2023, DOI: https://doi.org/10.1007/978-1-4842-9600-4
2. Mohan N., Undeland T., Robbins W., Power Electronics: Converters, Applications, and Design,
Wiley, 2007.

org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2
1007/978-981-19-4353-9
1007/978-3-031-09853-6
978-3-031-00292-2
13. Asadi F., Eguchi K., Electronic Measurement: A Practical Approach, Springer, 2021. DOI:
https://doi.org/10.1007/978-3-031-02021-6
14. https://bit.ly/3KPtUUR

3
Thyristors and Triacs
3.1 Introduction
Thyristor (or Silicon Controlled Rectifier, SCR) is an important solid-state switch. It is
a unidirectional device. This means that current can pass from anode to cathode only
(Fig. 3.1).
Triacs (Fig. 3.2) are bidirectional switches (current can go from MT1 to MT2 or from
MT2 to MT1). Being bidirectional makes triacs suitable for AC circuits.
This chapter studies the important circuits that can be made with thyristors and triacs.
3.2 Relaxation Oscillator with UJT
Relaxation oscillator is the most common use of Uni-Junction Transistor (UJT). The
relaxation oscillator can be used to trigger the thyristors.
A relaxation oscillator is shown in Fig. 3.3. Explain how the circuit shown in Fig. 3.3
works. Make the circuit shown in Fig. 3.3 and observe the waveform of different nodes.
What role is played by the potentiometer?
Observe the voltage of Emitter node (node E in Fig. 3.3) and measure the maximum
and minimum value of the observed waveform. For 2N2646, typical intrinsic standoff ratio
(η) is around 0.7. Therefore, peak value of Emitter voltage is around Vp = η·VBB +VD =
0.7 × 12 + 0.7 = 9.1V.
39

40 3 Thyristors and Triacs
Fig.3.1 Thyristor symbol
Fig.3.2 Triac symbol

3.3 Thyristor 41
Fig.3.3 Relaxation oscillator
with UJT
3.3 Thyristor
Thyristor is a unidirectional switch (Fig. 3.4). The user can apply a gate pulse to turn
on the thyristor. When the thyristor is on, the current goes from anode to cathode. The
thyristor conducts current until the voltage between the cathode and anode is reversed or
reduced below a certain threshold or holding value.
Circuits of this chapter used TIC106 thyristor. Pinout of TIC106 thyristor is shown in
Fig. 3.5.

Fig.3.4 In thyristors current flows from anode to cathode
Thyristors are operated in one of the following three states.
Forward conducting: This is a thyristor’s primary operating mode. Current flows from
anode to cathode until the current falls below a specific level, called the holding current.
Forward blocking: In this case Vanode −Vcathode > 0. However, lack of gate pulse causes
the thyristor block the flow of current.
Reverse blocking mode: In this case Vanode − Vcathode < 0 and no current (except of a
small leakage current of order of few micro amps) pass through the thyristor.
Let’s get started. Circuit shown in Fig. 3.6 helps you to understand how thyristor works.
Make the circuit shown in Fig. 3.6 (Set VG to 0 V). Use a DC voltmeter to monitor the
load voltage (i.e., VA −VB). Increase the VG slightly until the thyristor enters the forward
conducting mode (when DC voltmeter shows a voltage around 10–10.5 V the thyristor is
in the forward conducting mode). Measure the gate current (current through resistor RG)
and voltage drop across the anode–cathode of the thyristor. Disconnect the connection
between RG and gate terminal (Fig. 3.7) when the thyristor is in the forward conduction
mode. Does the thyristor continue to conduct current in this case?

3.4 Thyristor Turn Off Methods in DC Circuits 43
Fig.3.5 Pins of TIC106
thyristor
3.4 Thyristor Turn Off Methods in DC Circuits
Consider the circuit shown in Fig. 3.8. When you press the S1 push button, the thyristor
starts to conduct current and enters the forward conduction mode. When you press the
S2 push button, the load current starts to pass through the push button S2 and thyristor
current decreases to zero. When you release the push button S2, the thyristor is in the off
state and stays in the off state until the user press the push button S1 again.

Fig.3.6 Simple test circuit for a thyristor
Make the circuit shown in Fig. 3.8 and ensure that it works as expected. Press the
push button S1 and measure the voltage of different nodes. Release the push button S1
after measurement. Then press the push S2 and measure the voltage of different nodes.
Compare your measurements with hand analysis results.
Another technique to turn off a thyristor in a DC circuit is shown in Fig. 3.9. When
you press the S1 push button, the gate current flows and the thyristor enters the forward
conduction mode. This charges the capacitor C1 to around 10–10.5 V.

3.4 Thyristor Turn Off Methods in DC Circuits 45
Fig.3.7 Gate current is zero
When you press the S2 push button, the capacitor is connected to the thyristor and
applies a negative voltage it. This negative voltage cause the thyristor to enter the reverse
blocking mode and stops the load current.
Make the circuit shown in Fig. 3.9. Press the push button S1 and measure the voltage
of different nodes. Release the push button S1 after measurement. Then press the push
S2 and measure the voltage of different nodes. Compare your measurements with hand
analysis results.

Fig.3.8 Turning off the thyristor with a switch
3.5 Diac
The diac is a diode that conducts electrical current only after its break over voltage, VBO,
has been reached momentarily. I-V characteristic of a diac is shown in Fig. 3.10. Diacs
are usually used for triggering the triacs.
Let’s use a simple circuit to see how diacs behave. Make the circuit shown in Fig. 3.11.
Set V1 equal to 0 V and increase it with 3 V steps until the LED turns on (V 1 ≈ 30V
turns on the LED). Measure the voltage drop across the diac when the LED is turned on.

3.6 Pulse Generation with Diacs 47
Fig.3.9 Turning off the thyristor by applying a negative voltage to anode–cathode
Repeat the previous experiment with the polarity of V1 reversed (Fig. 3.12).
3.6 Pulse Generation with Diacs
You can use the diacs for pulse generation as well. Consider the circuit shown in Fig. 3.13.
The capacitor starts to charge through R1 and potentiometer. When voltage of capacitor
wants to go over the break over voltage of DB3 diac, the diac enters the conduction mode
and discharges the capacitor. Capacitor starts to charge again after the discharge and this
process repeats.

Fig.3.10 Typical current–voltage (I-V) curve for a diac
Fig.3.11 Simple circuit to test the behavior of a diac
Make the circuit shown in Fig. 3.13. Use an oscilloscope to observe the waveforms of
node A and B. What is the effect of potentiometer on circuit waveforms?

3.7 Dimmer Circuit 49
Fig.3.12 Applying negative voltages to the diac
3.7 Dimmer Circuit
A dimmer circuit is a circuit which can be used to control the intensity of incandescent
light bulbs, speed of small universal motors or amount of heat generated by a heater. A
dimmer works by essentially chopping parts out of the AC voltage.
A dimmer circuit is shown in Fig. 3.14. The triac is triggered when voltage of capacitor
C1 is bigger than the break over voltage of DB3 diac. Break over voltage of DB3 is around
30 V. The time instant that capacitor voltage reaches 30 V is controlled by potentiometer
and its series resistor R1. R2 and C2 form a snubber circuit and protest the triac.
Simulate the circuit shown in Fig. 3.14 and observe the waveforms of different nodes.
Study the effect of potentiometer on the load voltage. Don’t try to make this circuit on
breadboard. Realization of this circuit requires a printed circuit board and it must be tested
under the supervision of lab instructor.

Fig.3.13 Pulse generation with diac
3.8 Controlled Rectifiers
Thyrsitors can be used to make controlled rectifiers. Controlled rectifiers generally use a
pulse transformer to trigger the thyristors. Reference [1] shows how to make a controlled
rectifier with thyristors and an Arduino board.

Fig.3.14 Dimmer circuit
1. bit.ly/3sq9UBL
Wiley, 2007.
org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2
1007/978-981-19-4353-9
1007/978-3-031-09853-6

978-3-031-00292-2
https://doi.org/10.1007/978-3-031-02021-6

4
Power Supply Circuits
4.1 Introduction
All of the electronic circuits require an energy source to operate correctly. This chapter
studies different types of power supplies.
4.2 Half Wave Rectifier
A half wave rectifier circuit is shown in Fig. 4.1. The transformer used is a 12 V trans-
former (Fig. 4.2). Capacitor C1 is 1000 µF, 35 V. Make the circuit shown in Fig. 4.1. Use
an oscilloscope to observe the load voltage waveform. Use AC coupling of the oscillo-
scope to observe the load voltage ripple. Measure the frequency and peak-to-peak value
of ripple voltage. Compare the measured values with hand analysis results. What is the
relationship between ripple voltage frequency and frequency of input AC source? Use
a DC voltmeter to measure the average value of load voltage. What is the relationship
between peak value of secondary voltage and average value of load voltage?
4.3 Full Wave Rectifier
A full wave rectifier circuit is shown in Fig. 4.3. The transformer used is a 12 V trans-
former (Fig. 4.2). Capacitor C1 is 1000 µF, 35 V. Make the circuit shown in Fig. 4.3. Use
an oscilloscope to observe the load voltage waveform. Use AC coupling of the oscillo-
scope to observe the load voltage ripple. Measure the frequency and peak-to-peak value
of ripple voltage. Compare the measured values with hand analysis results. What is the
relationship between ripple voltage frequency and frequency of input AC source? Use
53

54 4 Power Supply Circuits
Fig.4.1 Half wave rectifier
Fig.4.2 RMS of the output voltage is 12 V
a DC voltmeter to measure the average value of load voltage. What is the relationship
between peak value of secondary voltage and average value of load voltage? What is the
difference between full wave and half wave rectifier?
You can use a diode bridge instead of using four separate diode. A sample diode bridge
and its equivalent circuit are shown in Figs. 4.4 and 4.5, respectively.
4.4 Symmetric Power Supply
The previous circuits provides positive voltages only. In this section, we want to study
the generation of symmetric outputs (i.e., both positive and negative voltages). Symmetric
power supplies require a center tap transformer.
The transformer required in this section is shown in Fig. 4.6. Waveforms of this
transformer are shown in Fig. 4.7.

4.4 Symmetric Power Supply 55
Fig.4.3 Full wave rectifier
Fig.4.4 Diode bridge

Fig.4.5 Schematic of a diode bridge
Fig.4.6 Center tap transformer with 12 V output
The circuit shown in Fig. 4.8 can be used for generation of symmetric voltages.
Capacitor C1 and C2 are 1000 µF, 35 V.
Make the circuit shown in Fig. 4.8. Use an oscilloscope to observe the load1 volt-
age waveforms. Use AC coupling of the oscilloscope to observe the load1 voltage ripple.
Measure the frequency and peak-to-peak value of ripple voltage. Compare the measured
values with hand analysis results. What is the relationship between ripple voltage fre-
quency and frequency of input AC source? Use a DC voltmeter to measure the average
value of load1 voltage. What is the relationship between peak value of secondary voltage
and average value of load1 voltage? Repeat the measurements for load2 as well.

4.5 Voltage Regulator ICs 57
Fig.4.7 Output voltage of center tap transformer
Fig.4.8 Power supply circuit with positive and negative voltages
4.5 Voltage Regulator ICs
Voltage regulators provide an accurate constant voltage for you. A +5 V voltage regulator
IC is shown in Fig. 4.9.
78xx and 79xx ICs are among the commonly used voltage regulator ICs. 78xx voltage
regulator ICs produce positive fixed DC voltage values, whereas, 79xx voltage regulator
ICs produce negative fixed DC voltage values. For example, 7805 provides a +5 V output

Fig.4.9 A +5 V voltage
regulator IC
while 7905 provides a −5 V output. Pinout 78xx and 79xx ICs are shown in Fig. 4.10.
For correct operation, absolute value of input voltage must be bigger than output voltage
by at least 2–3 V.
The circuit shown in Fig. 4.11 shows how to convert +12 V into +5 V. 7805 can take
input voltages in the [+7 V, +35 V] range and can give up to 1.5 A of output current.
Addition of a diode between input and output nodes (Fig. 4.12) is recommended.
The circuit shown in Fig. 4.13 shows how to convert −12 V into −5 V. 7905 can take
input voltages in the [−7 V, −35 V] range and can give up to 1 A of output current.
Addition of a diode between input and output nodes (Fig. 4.14) is recommended.
The circuit shown in Fig. 4.15 is a regulated ±5 V power supply.
Make the circuits shown in Figs. 4.12, 4.14 and 4.15. Measure the output voltages and
ensure that they are as expected.

4.5 Voltage Regulator ICs 59
Fig.4.10 Pinout of 78xx and 79xx ICs
Fig.4.11 Sample circuit with 7805

Fig.4.12 Addition of diode D1 is recommended
Fig.4.13 Sample circuit with 7905
4.6 Regulated Power Supply with High Output Current
and Short Circuit Protection
Output current of 78xx ICs is limited to 1.5 A. You can use the circuit shown in Fig. 4.16
to obtain more output current. Circuit shown in Fig. 4.16 is a regulated power supply
with high output current and short circuit protection. Short circuit current for Fig. 4.16 is
ISC =
VBE Q2
RSC
≈ 0.6
RSC
.
Make the circuit shown in Fig. 4.17. This circuit provides a +5 V output for the load
and output current is limited to around ISC =
VBE Q2
RSC
≈ 0.6
0.22 = 2.73A (Note that 7805
can handle up to 1.5 A only). Use a DC ammeter to measure the Iload, I1 and I2. Then
measure the short circuit current of the output and compare it with calculated value of
2.73A. Calculate the efficiency of this circuit (Remember that η = Pout
Pin
= Vin×Iin
RLoad ×ILoad
2 ).

4.8 Obtaining a High Regulated Output Voltage 61
4.7 Regulator with Adjustable Output
The circuit shown in Fig. 4.18 can be used to obtain a variable output voltage. Formula
for output voltage is shown in Fig. 4.18. This formula is correct when IR1 > 5IQ.
Let’s get started. Make the circuit shown in Fig. 4.19. Measure the minimum and max-
imum output voltages that this circuit can generate. Use a DC milli ammeter to measure
the IQ as well. Measure the output value for the case R1 = 3kΩ and R2 = 7kΩ.
4.8 Obtaining a High Regulated Output Voltage
You can use the circuit shown in Fig. 4.20 to obtain a high regulated output voltage.
Formula for output voltage is shown in Fig. 4.20. This formula is correct when IR1 ≥ 5IQ.
Remember that for correct operation, absolute value of input voltage must be bigger than
output voltage by at least 2–3 V, i.e., Vin − VX X
(
1 + R2
R1
)
+ IQ R2 > 3V .
Let’s get started. Make the circuit shown in Fig. 4.21 and measure the output volt-
age and IQ and IR1. Compare the measured output with value predicted by the VO =
VX X
(
1 + R2
R1
)
+ IQ R2 = 24 ×
(
1 + 390
470
)
+ IQ × 390 = 43.91 + IQ × 390 formula.
The circuit shown in Fig. 4.22 can be used to generate +5, 6.5, 8.3, 9.9 and 12 V.
Make the circuit shown in Fig. 4.22 and ensure that it gives the expected output voltages.
Fig.4.14 Addition of diode D1 is recommended

Fig.4.15 A power supply circuit with positive and negative regulated output voltages
Fig.4.16 Increasing the output current and protection against short circuit
Fig.4.17 Test circuit

4.9 Current Source Circuit 63
Fig.4.18 Obtaining a variable output voltage
4.9 Current Source Circuit
The circuit shown in Fig. 4.23 can be used as current source. Remember that for correct
operation, absolute value of input voltage must be bigger than output voltage by at least
2–3 V, i.e., Vin − VX X −
(
VX X
R1
+ IQ
)
Rload > 3V.
Let’s get started. The circuit shown in Fig. 4.24 can be approximated as a 5/47 =
106 mA current source. Make the circuit shown in Fig. 4.24. Connect different loads in
the [0 Ω, 120 Ω] range to the output and pay attention to value read by the milli ammeter.

4.10 LM317 Adjustable Regulator
LM317 is one of the commonly used voltage regulators. An adjustable voltage regulator
with LM317 is shown in Fig. 4.25. Output voltage for this circuit is given by: VO =
1.25×
(
1 + R2
R1
)
+(Iadj × R2).Iadj is typically 50 µA and negligible in most applications.
Make the circuit shown in Fig. 4.26. Measure the maximum and minimum value of
load voltage. Compare the measured values with values predicted using the VO ≈ 1.25 ×
(
1 + R2
R1
)
formula.
4.11 Overload Protection
The circuit shown in Fig. 4.27 can be used to avoid drawing currents beyond a certain
limit. When current drawn from the input source exceeds Imax =
VBE,Q1
R1 ≈ 0.6
R1
, the
transistor Q1 turns on. This turns on the thyristor as well. The relay is activated and dis-
connects the load current when the thyristor turns on. When load current is disconnected,
the LED turns on to inform the user. After solving the problem, the user needs to press
the normally close push button to reset the circuit.
Fig.4.20 Obtaining a high output voltage

4.11 Overload Protection 65
Fig.4.22 Obtaining +5, 6.5, 8.3, 9.9 and 12 V at the output
The reset push button can be placed in parallel with the thyristor as well (Fig. 4.28).
Note that the push button in Fig. 4.28 is a normally open push button. When overload
happens, you need to press the push button to reset the circuit.

Fig.4.23 Current source circuit
Let’s get started. Make the circuit shown in Fig. 4.29. Decrease the value of load
resistor from 50 Ω toward 20 Ω and measure the maximum current that can be drawn from
the source. Compare your measurement with value predicted by the Imax =
VBE,Q1
R1 ≈
0.6
R1
= 0.6
1 = 0.6A formula.
Protection against short circuit using relays is studied in [1].
4.12 Over Voltage Protection
The circuit shown in Fig. 4.30 can be used for overvoltage protection purposes. The
thyristor turns on when input voltage is big enough. You need to press the push button to
reset the circuit. Similar to the previous circuit, you can connect the reset push button in
parallel with the thyristor (Fig. 4.31).
Make the circuit shown in Fig. 4.30 or 4.31. Apply VIN = 6 V and VIN = 15 V to
the circuit and see what happens. Set the VIN = 0, then increase the VIN slightly and
measure the maximum input voltage that can be applied to the load.

4.13 Over Temperature Protection 67
4.13 Over Temperature Protection
The circuit shown in Fig. 4.32 or 4.33 can be used to disconnect the energy from a load
when temperature is beyond a certain level. When temperature rises, the NTC resistance
decreases and potential of positive terminal of Op Amp increases. Output of the Op Amp
is low (i.e., around 0 V) when potential of positive terminal is less than 8.2
8.2+4.7 × 12 =
7.63 V. Output of the Op Amp is high (i.e., around 12 V) when voltage of positive
terminal of the Op Amp is bigger than 7.63 V. The thyristor is triggered when output of
the Op Amp is high. The user needs to press the push button to reset the circuit.

Fig.4.25 Adjustable regulator with LM317
Make the circuit shown in Fig. 4.32 or 4.33. Use a soldering iron to heat the NTC
and observe the circuit behavior. At which temperature the circuit current is stopped? Use
hand analysis to obtain a relationship for current cut-off temperature of the circuit.
4.14 Voltage Multiplier Circuit
Voltage doubler and tripler circuits are shown in Figs. 4.34 and 4.35, respectively. These
circuits can’t provide much current and are used in low current applications.
Use a hand analysis and show that Figs. 4.34 and 4.35 are voltage doubler and tripler.
Make the circuit shown in Figs. 4.34 and 4.35 (the transformer secondary voltage is 12
VAC and working voltage of the capacitors is 63 V). Use a DC voltmeter to measure the
voltage of capacitors and compare them with your hand analysis.

4.14 Voltage Multiplier Circuit 69
Fig.4.27 Overload protection circuit (Reset button is in series with VIN source)

Fig.4.28 Overload protection circuit (Reset button is in parallel with the thyristor)

4.15 Simple Inverter Circuit 71
Fig.4.30 Over voltage protection circuit (Reset button is in series with VIN source)
4.15 Simple Inverter Circuit
The circuit shown in Fig. 4.36 is a simple inverter (i.e., DC to AC converter) circuit. Q2
and Q3 are switched with frequency of 50 Hz. The transformer used here is shown in
Fig. 4.2. Gate pulses applied to Q2 and Q3 are complement of each other.
Let’s get started. Explain how circuit shown in Fig. 4.36 works. Simulate the circuit
shown in Fig. 4.36. Observe the gate pulses of Q2 and Q3. Use an oscilloscope to observe
the load voltage waveform. Change the value of load and see its effect on the load voltage.
Ready to use EGS002 card can be used to make more accurate SPWM inverters [2].

Fig.4.31 Over voltage protection circuit (Reset button is in parallel with the thyristor)
Fig.4.32 Over temperature protection circuit (Reset button is in series with VIN source)

4.15 Simple Inverter Circuit 73
Fig.4.33 Over temperature protection circuit (Reset button is in parallel with the thyristor)
Fig.4.34 Voltage doubler circuit
Fig.4.35 Voltage tripler circuit

Fig.
4.36
Simple
square
wave
inverter
circuit

1. https://bit.ly/3QTtyAi
2. https://bit.ly/3skFFwp
3. https://bit.ly/3KLcpF6
4. https://bit.ly/45x1t67
5. https://bit.ly/45v9s4d
Wiley, 2007.
org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2
1007/978-981-19-4353-9
1007/978-3-031-09853-6
978-3-031-00292-2
https://doi.org/10.1007/978-3-031-02021-6

5
DC-DC Converters
5.1 Introduction
DC-DC converters take a DC voltage as input and generate a different DC voltage (i.e., a
DC voltage that is bigger or smaller than input) as output. This chapter studies some of
the important DC-DC converter circuits.
5.2 Boost Converter
The circuit shown in Fig. 5.1 shows a Boost converter circuit. The Boost converter pro-
vides a output voltage that is bigger than input voltage. The gate signal is a pulse with
amplitude of 5 V, frequency of 25 kHz and duty cycle of 0.6. You can use a signal
generator to make this pulse.
Analyze the circuit shown in Fig. 5.1 and calculate the average value of output voltage
and output voltage ripple using hand analysis. Make the circuit and measure the average
value of output voltage using a DC voltmeter. Then use an oscilloscope to measure the
output voltage ripple (connect the oscilloscope to load and use AC coupling to observe
the ripple only). Compare your measurements with hand analysis results. Calculate the
efficiency of the circuit as well (η = Pout
Pin
). Change the duty cycle and measure the average
value of output for different duty cycles.
A DC-DC converter requires a closed-loop control system to give a stable DC output.
Without a closed-loop control system, disturbances like: input voltage changes and output
load changes affect the output voltage. Closed-loop control system design for DC-DC
converters is studied in [1].
77

78 5 DC-DC Converters
Fig.5.1 Boost converter circuit
5.3 Buck Converter
We used discrete components to make a Boost converter in the previous example. Many
ICs were made to simplify making the DC-DC converters. You need to add few external
components to these ICs to make the desired converter. In this experiment, we will use
LM 2576 to make a Buck converter. Study the datasheet of this IC (This IC has 52 kHz
switching frequency). Functional block diagram of this IC is shown in Sect. 7.2 of [2].
Let’s get started. Make the circuit shown in Fig. 5.2. Measure the output voltage and
efficiency. Observe the waveform of diode D1 as well. Measure the frequency of observed
waveform.
See [3] to see another IC that can be used to make DC-DC converters.
Fig.5.2 Buck converter circuit

5.5 Voltage-Inverting Converter with MC33063 IC 79
Fig.5.3 Voltage inverting with TL7660 IC
5.4 Voltage-Inverting Converter with TL7660 IC
Sometimes you need a negative voltage to supply your circuit (i.e., circuits made with Op
Amps) but you have only one power supply (for example you have only one 12 V batter).
In these cases you can use TL7660 to convert a positive voltage into a negative voltage.
Note that TL7660 provides a small output current for you. It is suitable for light loads
only.
Let’s get started. Make the circuit shown in Fig. 5.3 (input voltage is less than 3.5 V).
Use a DC voltmeter to measure the average value of the output voltage. Connect different
loads to the output (VOUT node) and use an oscilloscope to observe the load voltage.
What happens to the load voltage waveform when the load current increases?
Repeat the experiment with the circuit shown in Fig. 5.4.
5.5 Voltage-Inverting Converter with MC33063 IC
You can use a MC33063 IC for voltage polarity reversal as well. This IC provides more
output current in comparison to TL7660. However, it requires more external components
in comparison to TL7660.
Let’s get started. Make the circuit shown in Fig. 5.5. Use a DC voltmeter to measure
the average value of the output voltage. Connect different loads to the output (VOUT node)
and use an oscilloscope to observe the load voltage. What happens to the load voltage
waveform when the load current increases?

Fig.5.4 Voltage inverting and doubling with TL7660 IC
Fig.5.5 Voltage inverting with MC33063 IC
5.6 Voltage Inverting Converter with 555 IC
Previous experiments introduced two ways to generate a negative voltage from a given
positive voltage. You can use the circuit shown in Fig. 5.6 as the third way of negative
voltage generation.

5.7 Voltage Doubler Circuit 81
Fig.5.6 Voltage inverting with 555 IC
5.7 Voltage Doubler Circuit
The circuit shown in Fig. 5.7 can be used to boost the input DC voltage by factor of
around 2. Note that this circuit can’t provide much output current for. It is suitable for
low power applications only. The TL7660 IC can be used as voltage doubler as well [4].

Fig.5.7 Voltage doubler with 555 IC
1. Asadi F., Eguchi K., Dynamics and Control of DC-DC Converters, Springer, 2018. DOI: https://
doi.org/10.1007/978-3-031-02502-0
2. https://bit.ly/45b3N2S
3. https://bit.ly/3E32LtP
4. https://bit.ly/45g6jVE
Wiley, 2007.
org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2

1007/978-981-19-4353-9
1007/978-3-031-09853-6
978-3-031-00292-2
https://doi.org/10.1007/978-3-031-02021-6

6
Filter and Comparator Circuits
6.1 Introduction
A comparator compares two voltages and indicate which is larger. A filter is a circuit that
separate some frequencies from others. This chapter studies the important comparator and
filter circuits.
6.2 Simple Comparator
The circuit shown in Fig. 6.1 compares the voltage V1 with 1
10+1 × 12V = 1.091 V.
When V1 is bigger than 1.091 V, the output will be high. When V1 is less than 1.091 V,
the output will be low.
Make the circuit shown in Fig. 6.1 and observe the input and output waveforms. Does
it work as expected? V1 is a sinusoidal signal with frequency of 1 kHz and peak value of
3 V.
Change the circuit to what shown in Fig. 6.2 and observe the input and output wave-
forms. Compare the waveforms with previous experiment. What is the difference between
this circuit and circuit shown in Fig. 6.1.
6.3 Window Comparator
A window comparator is a circuit that determines whether input signal is in a specific
interval. Block diagram of window comparator is shown in Fig. 6.3.
85

86 6 Filter and Comparator Circuits
Fig.6.1 Comparator circuit (input voltage is applied to positive terminal of the Op Amp)
Fig.6.2 Comparator circuit (input voltage is applied to negative terminal of the Op Amp)
The circuit shown in Fig. 6.4 determines whether Vin is in the

1
1+10 × 12V, 2.2
10+2.2 × 12 V

= [1.092V, 2.164 V] interval. Output is high (LED
is on) when input signal is in this interval.

6.3 Window Comparator 87
Fig.6.3 Block diagram of a window comparator
Fig.6.4 Window comparator for [1.092 V, 2.164 V] interval
Explain how circuit shown in Fig. 6.4 works. Then make the circuit and ensure that
it works as expected. Apply 0 VDC, 1.5 VDC, 2.5 VDC and a sinusoidal signal with
peak value of 3 V to the input and observe the output using an oscilloscope. Interpret the
observed waveforms.

6.4 Low Pass Filter
A simple passive low pass filter is shown in Fig. 6.5. Transfer function of this circuit
is H(s) =
VC1 (s)
Vin(s) =
1
C1s
R1+ 1
C1s
= 1
R1C1s+1 = 1
0.001s+1 . Cut-off frequency of this filter is
1
2π R1C1
= 159 Hz.
Let’s use MATLAB to draw the frequency response of the circuit shown in Fig. 6.5.
The code shown in Fig. 6.6 draws the frequency response for us. Output of this code is
shown in Fig. 6.7.
You can cascade two or more low pass filters in order to obtain a more accurate low
pass filter. In Fig. 6.8 two low pass filters are cascaded. Transfer function of this filter is
H(s) = Vout (s)
Vin(s) = 1
R1C1s+1 × 1
R2C2s+1 = 1
(R1C1s+1)(R2C2s+1) .
Let’s use MATLAB to draw the frequency response of the circuit shown in Fig. 6.8.
The code shown in Fig. 6.9 draws the frequency response for us. Output of this code is
shown in Fig. 6.10.
Fig.6.5 Low pass filter
Fig.6.6 MATLAB code

6.4 Low Pass Filter 89
Fig.6.7 Output of the MATLAB code
Fig.6.8 Cascaded low pass filters

Fig.6.9 MATLAB codes
Fig.6.10 Output of MATLAB code

6.4 Low Pass Filter 91
Fig.6.11 MATLAB code
Let’s draw Figs. 6.7 and 6.10 on the same graph. This helps us to compare them. The
code shown in Fig. 6.11 draws both of the transfer functions on the same graph. Output of
this code is shown in Fig. 6.12. Frequency response of circuits shown in Figs. 6.5 and 6.8
are shown with blue and red, respectively. Note that the red curve is steeper. Therefore,
the circuit shown in Fig. 6.12 is a more accurate low pass filter.

Let’s get started. Make the circuit shown in Figs. 6.5 and 6.8. Apply a sinusoidal
signal with amplitude of 1 V and measure the output amplitude for different frequencies.
Use MATLAB (see Sect. A.7 in Appendix A) to draw the frequency response graph of
obtained data.
6.5 High Pass Filter
A simple passive high pass filter is shown in Fig. 6.13. Transfer function of this circuit is
H(s) =
VR1 (s)
Vin(s) = R1
R1+ 1
C1s
= R1C1s
R1C1s+1 . Cut-off frequency of this filter is 1
2π R1C1
.
You can cascade two or more low high filters in order to obtain a more accurate high
pass filter. In Fig. 6.14 two high pass filters are cascaded. Transfer function of this filter
is H(s) = Vout (s)
Vin(s) = R1C1s
R1C1s+1 × R2C2s
R2C2s+1 = R1 R2C1C2s2
(R1C1s+1)(R2C2s+1) .
The MATLAB code shown in Fig. 6.15 draws the frequency response of the circuits
shown in Figs. 6.13 and 6.14 on the same graph. Output of this code is shown in Fig. 6.16.
Frequency response of circuits shown in Figs. 6.13 and 6.14 are shown with blue and red,
respectively. Note that the red curve is steeper. Therefore, the circuit shown in Fig. 6.14
is a more accurate high pass filter.
Fig.6.13 High pass filter

6.6 Band Pass Filter 93
Fig.6.14 Cascaded high pass filters
obtained data.
6.6 Band Pass Filter
Block diagram of a band pass filter is shown in Fig. 6.17.
The circuit shown in Fig. 6.18 is a cascade connection of a high pass filter with cut-
off frequency of 15.92 Hz and a low pass filter with cut-off frequency of 159.15 Hz.
Frequencies in the [15.92 Hz, 159.15 Hz] pass through this filter. Transfer function of
circuit shown in Fig. 6.18 is H(s) = R1C1s
R1C1s+1 × 1
R2C2s+1 .
The code shown in Fig. 6.19 draws the frequency response of the filter shown in
Fig. 6.18. Output of this code is shown in Fig. 6.20.

Fig.6.17 Block diagram of a band pass filter
You can use the Op Amps to obtain the desired pass band gain as well (Fig. 6.21).
Transfer function of the circuit shown in Fig. 6.22 is H(s) = (1 + R3
R4
) × (1 + R5
R6
) ×
R1C1s
R1C1s+1 × 1
R2C2s+1 . Compare this transfer function with the transfer function of circuit
shown in Fig. 6.18.

Fig.6.18 Band pass filter
The code shown in Fig. 6.23 draws the frequency response of the circuit shown in
Fig. 6.22. Output of this code is shown in Fig. 6.24. Compare this graph with the one
shown in Fig. 6.20.
obtained data.

Fig.6.21 Block diagram of a band pass filter with amplification

Fig.6.22 Band pass filter with amplification

org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2

1007/978-981-19-4353-9
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https://doi.org/10.1007/978-3-031-02021-6

7
Control of DC Motors
7.1 Introduction
A DC motor is an electrical motor that uses direct current to produce mechanical torque.
Control of DC motors (i.e., control of shaft speed or position) is relatively easy. This
makes the DC motors a good choice for many applications. This chapter shows how speed
and direction of rotation of a permanent magnet brushed DC motor can be controlled.
7.2 Direction of Rotation Indicator
You can use the circuit shown in Fig. 7.1 to show the rotation direction of the motor.
When motor rotates clockwise, one LED turns on and when the motor rotates counter
clockwise, the other one turns on.
Make the circuit shown in Fig. 7.1. Apply V1 = +12 V and V1 = −12 V and see the
behaviour of the circuit.
7.3 DC Motor Speed Control
The circuit shown in Fig. 7.2 can be used to control the speed of a small DC motor. You
can’t use this circuit to control the direction of rotation of motor. This circuit controls the
speed of motor only. The PWM pulses (Fig. 7.3) turns on and turns off the MOSFET.
In fact, the MOSFET control the average value of voltage applied to the armature and
average value of armature voltage changes the motor speed. The diode is required to
protect the MOSFET.
101

102 7 Control of DC Motors
Fig.7.1 Direction of shaft rotation indicator
You can use a small sense resistor to measure the motor current (Fig. 7.4). Voltage
across this sense resistor is proportional to the motor current. Sense resistor voltage is
representative of motor current.
Let’s get started. Make the circuit shown in Fig. 7.2 and apply a gate pulse with duty
cycle of 20% and frequency of 500 Hz (Fig. 7.3). Increase the duty cycle from 20% up
to 80% with 10% steps and observe the change of DC motor speed.
7.4 Control the Direction of Rotation
The circuit shown in Fig. 7.5 can be used to control the direction of rotation of the motor.
This circuit can’t be used to control the speed of the motor.
When the switch is in position A, transistor Q1 turns on and motor starts to rotate. Q2
is in cut-off mode in this case.
When the switch is in position B, transistor Q2 turns on and motor starts to rotate in
the reverse direction. Q1 is in cut-off mode in this case.
Let’s get started. Make the circuit shown in Fig. 7.5. Put the switch in position A and
B and see how the circuit behaves. Measure the voltages of the circuit and compare them
with hand analysis results.

7.5 Full-Bridge Driver 103
Fig.7.2 Speed control with MOSFET
Fig.7.3 PWM signal
7.5 Full-Bridge Driver
L298 is a full bridge driver. You can use it to control the direction and speed of two
separate DC motor. Operating supply voltage of L298 is up to 46 V and it can handle up
to 4 A of current. L298 is used in closed-loop rotor position control systems as well.

Fig.7.4 Voltage of RSENSE is a representative of motor current
L298 pinout is shown in Fig. 7.6. The IN1 and IN2 pins control the direction of rotation
for motor 1. Similarly, the IN3 and IN4 pins control the direction of rotation for motor
2. PWM signal for first motor is applied to ENA pin. PWM signal for second motor
is applied to ENB pin. Armature of first motor is connected to OUT1 and OUT2 pins.
Armature of second motor is connected to OUT3 and OUT4 pins. Motor power supply is
connected to VC and GND pins. VCC is connected to +5 V.
Let’s get started. Make the circuit shown in Fig. 7.7. Connect the ENA pin to a pulse
with frequency of 500 Hz and duty cycle of 20% (Fig. 7.8). Increase the duty cycle from
20% up to 80% with 10% steps and observe the change of DC motor speed. RSENSE can
be replaced with a short circuit. Voltage drop across RSENSE is representative of motor
current (VRsense = RSE N SE × Imotor ).

7.5 Full-Bridge Driver 105
Fig.7.5 Control of direction of rotation
Fig.7.6 Pins of L298 IC

Fig.7.7 Test circuit for L298 IC
Fig.7.8 PWM signal
Connect the IN1 and IN2 to GND and VCC, respectively (Fig. 7.9) and repeat the
experiment. Note that this time direction of rotation of the motor is the reverse of previous
case.
Connect both of IN1 and IN2 to ground (Fig. 7.10) and repeat the experiment. What
happens?
7.6 Speed Control of Universal Motors
The universal motor is a type of electric motors that can operate on either AC or DC
power. A dimmer (Fig. 7.11) can be used to control the speed of universal motors. Simu-
late the circuit shown in Fig. 7.11 and observe the waveform of different nodes. You can
use a 484 Ω resistor as load. Don’t try to make this circuit on breadboard. Realization of
this circuit requires a printed circuit board and it must be tested under the supervision of
lab instructor.

7.7 Stepper Motor and BLDC Motor Driver 107
Fig.7.9 IN1 and IN2 are 0 and +5 V, respectively
Fig.7.10 Both of IN1 and IN2 are 0 V
7.7 Stepper Motor and BLDC Motor Driver
Stepper and BLDC motors can be controlled quite easy with the aid of cheap ready to
use drivers. Refer to Chap. 8 of [1] for more information.

Fig.7.11 A dimer circuit can be used to control the speed of a DC motors
1. Asadi F., Essential of Arduino Boards Programming: Step-by-Step Guide to Master Arduino
Boards Hardware and Software, Apress, 2023, DOI: https://doi.org/10.1007/978-1-4842-9600-4
2. Mohan N., Advanced Electric Drives: Analysis, Control, and Modeling Using MATLAB /
Simulink, Wiley, 2008.
org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2
1007/978-981-19-4353-9
1007/978-3-031-09853-6
978-3-031-00292-2

https://doi.org/10.1007/978-3-031-02021-6
14. https://bit.ly/3qESDo6
15. https://bit.ly/3KIANre

8
Delay Circuits
8.1 Introduction
Sometimes you need to turn on/off a load with a certain delay after a specific event. For
instance, consider the staircase corridor lighting system: when you press the key, the lights
are turned on for a specific time (typically 2–3 min.). Then they turn off automatically.
This chapter shows how different types of delay circuits can be made.
8.2 Delay Circuit with Transistor (Normally on Circuit)
The LED is on in Fig. 8.1. When you press the push button, the LED turns off for a
while and it turns on again after a delay. Amount of delay is determined by the capac-
itor C1 and Thevenin resistance seen from its terminals. The potentiometer affects the
Thevenin resistance seen from the capacitor. Therefore, we can say that amount of delay
is determined by the potentiometer.
Make the circuit shown in Fig. 8.1. Measure the minimum and maximum delays
that you can generate with this circuit. Replace the 1000 µF capacitor with a 2200 µF
capacitor and repeat the experiment. What is the relationship between the results of two
experiments? Use hand analysis to obtain a formula for the amount of delay. Explain how
this circuit works.
111

112 8 Delay Circuits
Fig.8.1 Delay circuit with BJT (by default the transistor is on)
8.3 Delay Circuit with Transistor (Normally Off Circuit)
The LED is off in Fig. 8.2. When you press the push button, the LED turns on for a
while and it turns off again after a delay. Amount of delay is determined by the capac-
itor C1 and Thevenin resistance seen from its terminals. The potentiometer affects the
Thevenin resistance seen from the capacitor. Therefore, we can say that amount of delay
is determined by the potentiometer.
Make the circuit shown in Fig. 8.2. Measure the minimum and maximum delays
that you can generate with this circuit. Replace the 1000 µF capacitor with a 2200 µF
capacitor and repeat the experiment. What is the relationship between the results of two
experiments? Explain how this circuit works.

8.4 Delay Circuit with 555 IC 113
Fig.8.2 Delay circuit with BJT (by default the output transistor Q2 is off)
8.4 Delay Circuit with 555 IC
The mono-stable circuit shown in Fig. 8.3 can be used to generate delay. The output by
default is at low level (i.e., 0 V). When you press the push button, the output becomes
high (i.e., VCC) for duration of t = 1.1 × R2 × C1. After t = 1.1 × R2 × C1, the output
returns to low level.
Make the circuit shown in Fig. 8.3. Press the push button and measure the amount of
delay that you observe after releasing the push button. Use an oscilloscope to observe the
waveforms of the circuit.

Fig.8.3 Monostable circuit with 555 IC
Output of 555 can stimulate a relay. In Fig. 8.4 the red LED is on by default. When
you press the push button the green led turns on for duration of t = 1.1 × R2 × C1. After
t = 1.1 × R2 × C1 the red led turns on again.
Make the circuit shown in Fig. 8.4 and ensure that it works as expected.
8.5 555 Timer IC Based Circuit Design
NI® Multisim™ software can be used to design the 555 based circuits. The tool can be
accessed in the Tools menu (Fig. 8.5). You can use this tool to design Astable (Fig. 8.6)
or Mono stable (Fig. 8.7) circuits.

8.5 555 Timer IC Based Circuit Design 115
Fig.8.4 Output of 555 IC can stimulate a relay
Fig.8.5 Tools circuit
wizards 555 timer wizard

Fig.8.6 Astable circuit design
Fig.8.7 Monostable circuit design

1. Bell D., Solid State Pulse Circuits, Prentice Hall, 2008.
org/10.1515/9783110740653
8220-5
10.1007/978-3-031-25122-1
978-3-031-24552-7
https://doi.org/10.1007/978-3-030-89850-2
1007/978-981-19-4353-9
1007/978-3-031-09853-6
978-3-031-00292-2
https://doi.org/10.1007/978-3-031-02021-6

Drawing Graphs with MATLAB®
A.1 Introduction
This appendix shows how to draw different types of graphs with MATLAB.
A.2 fplot Command
Assume that you want to draw the graph of sin(x) for [0, 2π] interval. The commands
shown in Fig. A.1 do this job for you. Output of this code is shown in Fig. A.2.
You click on any point in order to read its coordinate (Fig. A.3).
A.3 Plotting the Graph of a Numeric Data
In the previous section you learned how to draw the graph of a symbolic function. In this
section we learn how to draw the graph of a numeric data. Plotting the graph of a numeric
data is very simple in MATLAB. You need to use the plot command.
Let’s make a numeric data (Fig. A.4).
Fig.A.1 fplot command can
be used to draw symbolic
expressions
© The Editor(s) (if applicable) and The Author(s), under exclusive license
to Springer Nature Switzerland AG 2024
Electrical Engineering, https://doi.org/10.1007/978-3-031-50773-1
119

Industrial Electronic Circuits Laboratory Manual (Synthesis Lectures on Electrical Engineering)

Industrial Electronic Circuits Laboratory Manual (Synthesis Lectures on Electrical Engineering)

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