Practical MOSFET Electronics Theory, LTspice Simulation, and Hands-On Projects
Dogan Ibrahim
Practical MOSFET Electronics Theory, LTspice Simulation, and Hands-On Projects
● Dogan Ibrahim
● This is an Elektor Publication. Elektor is the media brand of Elektor International Media B.V.
PO Box 11, NL-6114-ZG Susteren, The Netherlands Phone: +31 46 4389444
● All rights reserved. No part of this book may be reproduced in any material form, including photocopying, or
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● Declaration
The author and publisher have used their best efforts in ensuring the correctness of the information contained in this book. They do not assume, or hereby disclaim, any liability to any party for any loss or damage caused by errors or omissions in this book, whether such errors or omissions result from negligence, accident or any other cause.
● British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
● I SBN 978-3-89576-777-7 Print
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● © Copyright 2026 Elektor International Media www.elektor.com
Editor: Elektor Team Prepress Production: D-Vision, Julian van den Berg Printers: Ipskamp, Enschede, The Netherlands
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Contents
Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice . . . . . . . . . 13 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.2 Installing the LTspice on Windows PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.3 Running the LTspice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.4 Creating a new schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.5 Resistor-inductor-capacitor (RLC) transient circuit . . . . . . . . . . . . . . . . . . . . . . . 20 1.6 Semiconductor diode (P-N junction) fundamentals . . . . . . . . . . . . . . . . . . . . . . . 26 1.6.1. Semiconductor Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.7 Project 1 – Diode – LED circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.8 Project 2 – Diode clamping circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.9 Project 3 – Diode full wave rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Chapter 2 • Transistor Overview – BJTs and MOSFETs . . . . . . . . . . . . . . . . . . . . . . 38 2.1 Why Transistors? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.2 Brief Introduction to BJTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.3 NPN and PNP operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.1 NPN Transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.3.2 PNP Transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.3.3 Comparison of NPN and PNP operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.4 Transistor operating regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.4.1. Cutoff region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.4.2 Active region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.4.3. Saturation region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.5 Drawing the IC -VCE graph of a transistor using LTspice . . . . . . . . . . . . . . . . . . . . 43 2.6 Project 1 – Transistor as a switch – LED control . . . . . . . . . . . . . . . . . . . . . . . . . 44 2.7 Project 2 – Small signal transistor amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.8 Limitations of BJTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2.9 Introduction to MOSFETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.10 Why MOSFETs dominate modern electronics . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.11 Comparison of BJTs and MOSFETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
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Chapter 3 • MOSFET Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.2. MOSFET structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.3. MOSFET operating regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3.1 Cutoff region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 3.3.2 Triode (Linear) region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.3.3 Saturation region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.4 Project 1 – n-channel E-MOSFET switch – LED control . . . . . . . . . . . . . . . . . . . . . 61 3.5 Project 2 – p-channel E-MOSFET switch – LED control . . . . . . . . . . . . . . . . . . . . . 63 3.6 Project 3 – Automatic dark sensor with relay . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 3.7 Project 4 – Reed switch door security system . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.8 Project 5 – ON-OFF temperature control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.9 Project 6 – Smart safety box - Tilt switch and buzzer . . . . . . . . . . . . . . . . . . . . . 74 3.10 Project 7 – Touch controlled buzzer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.11 Project 8 – PIR sensor with relay output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.12 MOSFET and Pulse Width Modulation (PWM) – Driving large loads PWM . . . . . . . . 79 3.12.1 Project 9 – Small brushed DC motor speed control . . . . . . . . . . . . . . . . . . . . . 85 3.12.2 Project 10 – Temperature controlled fan (DC motor) . . . . . . . . . . . . . . . . . . . 87 3.12.3 Project 11 – DC Motor speed and direction control – MOSFET H-Bridge . . . . . . 89 Chapter 4 • MOSFET Small Signal Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.2 MOSFET transfer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 4.2.1 D-MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 4.2.2 E-MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 4.3 Small signal MOSFET amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 4.3.1 Small signal model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 4.4 Drain current – Drain voltage characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4.4.1 Biasing the MOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 4.4.2 Example design of a small signal amplifier – common-source amplifier . . . . . . . 109 4.4.3 Multi-stage amplifier design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.4.4 2-stage MOSFET amplifier design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
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4.4.5 Common source amplifier without source bypass capacitor . . . . . . . . . . . . . . . 118 4.4.6 Other MOSFET amplifier configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Chapter 5 • MOSFET Oscillator Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.2 Astable multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 5.2.1 Output oscillation frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2.2 Project 1 – Example multivibrator design . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2.3 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.2.4 Constructing the circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.3 MOSFET Colpitts oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 5.3.1 Circuit diagram and equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 5.3.2 Project 2 – Example design of Colpitts oscillator . . . . . . . . . . . . . . . . . . . . . . 128 5.3.3 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 5.3.4 Construction on a breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.4 Hartley oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 5.4.1 Circuit diagram and equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 5.4.2 Project 3 – Example design of Hartley oscillator . . . . . . . . . . . . . . . . . . . . . . . 134 5.4.3 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 5.4.4 Construction on a breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 5.5 MOSFET phase shift oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 5.5.1 Project 4 – Example design of phase shift oscillator . . . . . . . . . . . . . . . . . . . . 139 5.5.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 5.5.3 Construction on a breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 5.5.4 Driving an LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 5.6 Crystal Pierce oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 5.6.1 Project 5 – Example Pierce oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.6.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 5.6.3 Construction on a breadboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 Chapter 6 • MOSFET Logic Gates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.2 NOT gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
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6.3 NAND gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.4 NOR gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.5 AND gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 6.6 OR gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.7 Project 1 – NAND gate with LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.8 Project 2 – NOT gate with LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 6.9 Project 3 – NOR gate with LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 6.10 Project 4 – OR gate with LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 6.11 Project 5 – AND gate with LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 6.12 Project 6 – Alarm system with buzzer output . . . . . . . . . . . . . . . . . . . . . . . . . 158 Chapter 7 • MOSFETs in Power Supply Applications . . . . . . . . . . . . . . . . . . . . . . . 161 7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 7.2 Power MOSFET data sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 7.3 DC to DC converters using MOSFETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 7.3.1 DC to DC Buck converter principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 7.4 The NE555 Astable multivibrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 7.4.1 NE555 Astable online calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 7.4.2 Astable circuit with duty cycle less than or equal to 50% . . . . . . . . . . . . . . . . 176 7.5 Project 1 – DC to DC Buck (step down) converter . . . . . . . . . . . . . . . . . . . . . . . 178 7.5.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 7.5.2 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7.6 Project 2 – DC to DC Boost (step up) converter . . . . . . . . . . . . . . . . . . . . . . . . 185 7.6.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 7.6.2 Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Chapter 8 • MOSFET Audio Power Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 8.1 Overview – Types of power amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 8.1.1 Class A MOSFET Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 8.1.2 Class B MOSFET Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 8.1.3 Class AB MOSFET Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 8.1.4 Class D MOSFET Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 8.1.5 Class C Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
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8.2 MOSFET audio power amplifier characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 193 8.2.1 Complementary and quasi-complementary output stages . . . . . . . . . . . . . . . . 193 8.2.2 Biasing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 8.2.3 Gate Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 8.2.4 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 8.2.5 Heat Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.2.6 Clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.2.7 Loudspeaker Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 8.3 1W Class A audio power amplifier using a MOSFET . . . . . . . . . . . . . . . . . . . . . . 196 8.3.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 8.4 1.5W Class AB audio power amplifier using a MOSFET . . . . . . . . . . . . . . . . . . . 202 8.5 10W MOSFET audio power amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 8.6 Very high power MOSFET Class D audio power amplifiers . . . . . . . . . . . . . . . . . 208 8.6.1 Basic features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 8.6.2 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 8.6.3 Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 List of components used in projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
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Preface The Metal-Oxide-Semiconductor Field-Effect Transistor, more commonly known as the MOSFET, is one of the most important electronic components used in modern circuit design. MOSFETs are found in power supplies, motor controllers, amplifiers, oscillators, digital logic circuits, microprocessors, communication systems, and many other electronic products. Their ability to switch quickly, consume very little input power, and control large currents makes them essential in both low-power and high-power electronic systems. This book has been written to provide a practical and easy-to-follow introduction to MOSFETs and their applications. It is intended for students, technicians, hobbyists, engineers, and anyone interested in learning how MOSFET circuits work. The aim is to explain the theory clearly, then reinforce the ideas through simulation and practical projects. Instead of presenting MOSFETs only as theoretical semiconductor devices, this book shows how they are actually used in real electronic circuits. The book begins with semiconductor fundamentals and an introduction to LTspice. Before studying MOSFETs in detail, it is useful to understand the basic behaviour of semiconductor materials and simple devices such as diodes. The first chapter therefore introduces semiconductor principles, diode operation, and basic circuit simulation. LTspice is used throughout the book because it allows circuits to be tested virtually before they are built on a breadboard. Readers are guided through installing LTspice, creating schematics, running simulations, and plotting voltage and current waveforms. Simple projects such as an LED diode circuit, a diode clamping circuit, and a full-wave rectifier help establish the foundation needed for later MOSFET circuits. The second chapter introduces transistors in general, beginning with bipolar junction transistors. BJTs are discussed because they provide a useful comparison with MOSFETs. The chapter explains NPN and PNP operation, transistor operating regions, switching behaviour, and small signal amplification. Practical projects include using a transistor as a switch to control an LED and designing a small signal transistor amplifier. These examples help the reader understand why MOSFETs have largely replaced BJTs in many modern applications, particularly where high input impedance, low power consumption, and efficient switching are required. The main study of MOSFETs begins with their structure and operating principles. The book explains the differences between depletion-mode and enhancement-mode MOSFETs, as well as N-channel and P-channel devices. The cutoff, triode, and saturation regions are described so that the reader can understand when a MOSFET is OFF, when it behaves like a switch, and when it can be used for amplification. These ideas are then supported by practical switching projects using both N-channel and P-channel enhancement MOSFETs to control LEDs.
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Preface
A major feature of this book is its project-based approach. The MOSFET projects begin with simple switching circuits and gradually progress to more practical control systems. The automatic dark sensor project uses a light-dependent resistor and a MOSFET to activate a relay when the light level falls, demonstrating how MOSFETs can be used in automatic lighting and sensing applications. The reed switch door security system shows how a MOSFET can respond to a magnetic door sensor and activate an alarm or output device. The ON-OFF temperature control project introduces temperature sensing and switching, showing how MOSFETs can be used in thermostatic control circuits. Other sensor and alarm projects are included to show how versatile MOSFETs can be in practical electronics. The smart safety box project uses a tilt switch and buzzer to detect movement or change of position. The touch-controlled buzzer demonstrates how a MOSFET can respond to a very small control signal and drive an audible output. The PIR sensor with relay output project introduces motion detection and shows how MOSFETs can interface with sensors used in security, automation, and lighting systems. These projects are designed to help the reader understand not only the MOSFET itself, but also how it connects to realworld input and output devices. Pulse Width Modulation is introduced as an important technique for controlling larger loads efficiently. The book includes projects on small brushed DC motor speed control, a temperature-controlled fan, and DC motor speed and direction control using a MOSFET H-bridge. These projects are particularly useful for readers interested in robotics, model control, cooling systems, and automation. They show how MOSFETs can be used not only to switch a motor ON and OFF, but also to vary its speed and reverse its direction. MOSFET small signal amplifiers are then studied in detail. The book explains MOSFET transfer characteristics, small signal models, drain current and drain voltage characteristics, biasing methods, common-source amplifier design, and multi-stage amplifiers. These sections are intended to help the reader understand how MOSFETs can amplify weak signals. Example designs show how component values are chosen and how the amplifier performance can be simulated before construction. Oscillator circuits form another important part of the book. MOSFET astable multivibrators, Colpitts oscillators, Hartley oscillators, phase shift oscillators, and crystal Pierce oscillators are introduced with practical design examples. These circuits demonstrate how MOSFETs can be used to generate square waves and sinusoidal signals. The projects include simulation and breadboard construction, allowing the reader to compare theoretical calculations with actual circuit performance. The oscillator projects also introduce important concepts such as feedback, frequency-determining components, waveform generation, and frequency stability. The book also explains the use of MOSFETs in digital logic gates. NOT, NAND, NOR, AND, and OR gates are presented, followed by practical projects using LEDs and a buzzer output. These projects show how MOSFETs can be used to perform basic logical operations and how simple digital circuits can be built from discrete components. The alarm system with
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Practical MOSFET Electronics
buzzer output combines logic concepts with a practical application, helping the reader see how digital decision-making can be used in real circuits. Power supply applications are covered in a later chapter. Since MOSFETs are widely used in switching power supplies, the book introduces power MOSFET data sheets, DC-to-DC converter principles, and the use of the NE555 timer as an astable waveform generator. Practical buck and boost converter projects show how MOSFETs can be used to step DC voltages down or up efficiently. These projects introduce important power electronics concepts such as duty cycle, inductors, switching action, output filtering, and efficiency. The final chapter introduces MOSFET audio power amplifiers. Different amplifier classes are described, including Class A, Class B, Class AB, Class D, and Class C amplifiers. The chapter also discusses practical design considerations such as complementary and quasicomplementary output stages, biasing, gate drive, power supply requirements, heat dissipation, clipping, and loudspeaker loading. A Class A MOSFET audio power amplifier project is included to demonstrate how MOSFETs can be used to drive an audio load and how theoretical design considerations affect practical amplifier performance. Throughout the book, LTspice simulations are used alongside practical construction. This allows the reader to design and test circuits before building them physically. Simulation also makes it easier to observe voltages, currents, waveforms, switching behaviour, amplifier gain, oscillator frequency, and power supply performance. By comparing simulated results with practical circuit operation, readers can develop a deeper understanding of MOSFET circuits and improve their design skills. This book does not assume advanced semiconductor knowledge. The topics are introduced gradually, beginning with basic semiconductor and transistor principles before moving into MOSFET switching, amplification, oscillation, digital logic, power conversion, motor control, and audio amplification. Each chapter builds on the previous one, and the projects have been selected to give the reader useful practical experience in a wide range of MOSFET applications. It is hoped that this book will help readers gain both confidence and competence in working with MOSFETs. By the end of the book, the reader should understand how MOSFETs operate, how to select suitable devices, how to simulate MOSFET circuits, and how to build practical MOSFET-based projects. The knowledge gained from these examples can then be applied to many other areas of electronics, from simple switching circuits to more advanced control, power, audio, and digital systems.
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
Chapter 1 • S emiconductor Fundamentals and Introduction to LTspice 1.1 Overview This chapter introduces the fundamental concepts of semiconductor devices and provides a practical foundation for circuit simulation using LTspice, one of the most widely used electronic circuit simulation tools. Understanding semiconductor behaviour is essential for the study of modern electronics, as semiconductor devices form the building blocks of nearly all electronic systems, from simple power supplies to advanced computing and communication technologies. Alongside the theoretical principles, this chapter emphasizes the use of simulation tools to analyse and verify circuit performance before physical implementation. The chapter begins with an introduction to LTspice, familiarising readers with its interface, key features, and role in electronic circuit design. LTspice enables engineers and students to model circuits, predict their behaviour, and troubleshoot potential design issues in a virtual environment. By learning the basic functions of the software, readers gain the ability to create schematic diagrams, configure simulation settings, and interpret simulation results effectively. This provides a valuable bridge between theoretical circuit analysis and practical design applications. Following the introduction, readers are guided through the process of running a simple simulation. This initial exercise demonstrates the fundamental workflow involved in circuit modelling, including component selection, circuit construction, simulation setup, and result interpretation. Through this process, readers develop confidence in using simulation software and gain an appreciation of how computational tools can be used to evaluate circuit performance quickly and accurately. The ability to simulate circuits before physical construction reduces development time, lowers costs, and helps identify design errors at an early stage. The discussion then focuses on diodes, one of the simplest and most important semiconductor components. The operating characteristics of diodes are examined, including their ability to conduct current in one direction while restricting current flow in the opposite direction. Particular attention is given to the current-voltage relationship of the diode and the practical implications of its nonlinear behaviour. Understanding diode operation is crucial for a wide range of electronic applications, including signal processing, voltage regulation, and power conversion. The chapter also explores voltage and current plotting, which are essential techniques for analysing circuit behaviour. Readers learn how to display and interpret graphical representations of electrical signals within LTspice. Voltage and current waveforms provide important insights into circuit operation, allowing engineers to observe how signals change over time and under different conditions. By understanding these graphical outputs, readers can evaluate component performance, verify design objectives, and gain a deeper understanding of circuit dynamics.
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Practical MOSFET Electronics
The chapter concludes with practical diode-based projects that integrate the concepts and techniques introduced throughout the chapter. These projects provide hands-on experience in circuit design, simulation, and analysis, reinforcing theoretical knowledge through practical application. By combining LTspice simulation tools with an understanding of semiconductor fundamentals, readers develop valuable skills that can be applied to more advanced electronic circuits and systems. Overall, this chapter establishes a strong foundation in semiconductor principles and circuit simulation, preparing readers for the study of increasingly sophisticated electronic devices and applications.
1.2 Installing the LTspice on Windows PC Most of the circuits designed in this book will be constructed and tested on a breadboard, and at the same time simulated using the popular LTspice circuit simulator package. In the next sections you will learn how to install the LTspice on your PC. Then, the simulation of some simple circuits will be shown in later sections to familiarize the readers with using the LTspice. At the time of writing this book the latest version of the LTspice was 26.0.2, known as Version 26. The installation steps are: • Go to web site: https://www.analog.com/en/resources/design-tools-and-calculators/LTspicesimulator.html • Scroll down and click on the Download link to download the installation file. • Double click on the file to install the LTspice. After the installation, the icon shown in Figure 1.1 should appear on your desktop,
Figure 1.1 LTspice icon
1.3 Running the LTspice Double click on the icon to start LTspice. Figure 1.2 shows the start-up screen. At this stage, you will see that almost all of the menu options are greyed out and are not available, except the File, View, Tools, and Help. For now, click Help -> About LTspice to display the version number (Figure 1.3)
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
Figure 1.2 LTspice start up screen
Figure 1.3 LTspice version number
1.4 Creating a new schematic • Before creating a new schematic, it is important to know how to specify the units of resistors, capacitors, and inductors used to be used in our circuit. Table 1.1 shows how the valid units. Note that the unit prefixes are not case sensitive, for example k and K are interpreted the same. Unit prefix
Unit
Multiple
T
tera
1012
G
giga
109
Meg
mega
106
k
kilo
103
m
milli
10-3
u
micro
10-6
n
nano
10-9
p
pico
10-12
f
femto
10-15
Table 1.1 LTspice units
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Practical MOSFET Electronics
To create a new schematic, click File -> New Schematic, or press Cntrl+N, or click the icon with the + sign at the top left hand side of the top menu. You will be presented with a screen as shown in Figure 1.4. The screen is divided into two parts to make it clear. The brief function of each button is displayed in this figure for quick reference. At the top part of the screen, we have the menu items and below them are the buttons or icons).
Figure 1.4 New schematic screen The following short key combinations can be used to access the menu buttons: New schematic Open Save Print Configure analysis Zoom Zoom back Zoom to fit Wire Ground Resistor Capacitor Inductor Diode Component Label net Text Spice directives Delete mode
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-
Cntrl+N Cntrl+O Cntrl+S Cntrl+P A Cntrl+Z Cntrl+B Space F3 G R C I D F2 F4 T S F5 or DEL
Duplicate mode Move mode Search mode Search
-
F6 F7 F8 Cntrl+F
Example simulation – Charging RC transient Perhaps the easiest way to learn how to simulate an electronic circuit is to go through an example. First of all, we have to create the schematic of the circuit to be simulated on the LTspice, and then the circuit can easily be simulated, displaying voltages, currents, waveforms etc in the circuit. In this section a simple resistor-capacitor (RC) transient charging circuit is simulated. Drawing the schematic: The steps are: • Start LTspice • Click File -> New Schematic • We will make the background as white. wire colour Black, and the screen background colour White, so that the schematics are clearly visible when the book is printed. To change the wire colour, click Tools -> Colour Preferences, Select Wires as the Selected item and set the red, green and blue to 0 so that the wire colour is black. Also, select Background as the Selected item and set Red, Green and Blue to 255 so that the background colour is white. • You can also make the graph lines thicker by clicking Tools -> Settings and then click to select tab Waveforms. Set the Data trace width to a higher value (e.g. 3) • Click on the resistor symbol to place resistors R1. Notice that the resistor should be rotated by 90 degrees. This is done before it is placed in its final position by typing Cntrl+R. Press ESC on the keyboard or right click your mouse button to exit. You can make the components smaller or larger my scrolling the mouse wheel. If you want to change the position of a component, click on button Move mode (or F7), click on the component to be moved and move it to desired position. Press ESC on keyboard or right click your mouse button to exit the Move mode. • Now, we will place the capacitor C1. Click on the capacitor symbol and place it next to the resistor. Press ESC on the keyboard or right click your mouse button to exit. • Click Voltage Source and place it at the left-hand side of the resistor and capacitor.
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Practical MOSFET Electronics
• Click to insert a Ground symbol under the voltage source • Join the components • Right click on resistor, click Select Resistor and set its value to 2 kΩ • Right click on capacitor and set its value to 1 µF • You can click the Move Mode menu option to move the labels around. • Click on the Voltage Source and set it to 5 V • Click menu option net and insert label VC at the output of the circuit • Figure 1.5 shows the final schematic with the components labelled
Figure 1.5 Join and label the components • This completes the design of the schematic. The next step is the simulation. Simulation: • Click Run/pause and select Transient. • Set the Stop time to 12m • Click to Skip initial operating point solution (Figure 1.6)
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
Figure 1.6 Transient mode settings • Click OK. You should see an empty graph. Place the voltage probe at the output point (VC). The time response of the voltage across the capacitor will be displayed. We can insert a title for the graph. Click right on the graph and then select Notes & Annotations -> Text and enter the text Voltage across the capacitor (Figure 1.7) and set its colour to red. Right click on the graph and enable View -> Grid. Click on the horizontal axis and change the final time (Right) to 10ms. Click Tools -> Color Preferences and select Waveform. Set the axis colours to 0 so that the axis labels are displayed in bold black. Figure 1.8 shows the final graph.
Figure 1.7 Enter a graph title
Figure 1.8 Voltage across the capacitor
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Practical MOSFET Electronics
The rise time of an RC circuit is the point where the voltage across the capacitor rises from 0V to about 63.2% of its final value. The rise time can also be found graphically by drawing a tangent to its rising slope and finding its intersection point with its final value (see Figure 1.9 where only the initial part of the graph is shown). Right click on the graph and select Notes & Annotations -> Line and draw a line tangent to the rising response. Then draw a vertical line from that point to the horizontal axis. Here, the rise time is found to be about 2ms.
Figure 1.9 Finding the time constant The theory The voltage across the capacitor in an RC circuit when a step input is applied is given by: VC = V1(1-e-t/RC) Where VC is the voltage across the capacitor and V1 is the applied step input voltage. In this example the formula becomes: VC = 5(1-e-t/0.002) The time constant of an RC circuit is given by, T = RC. With the component values of R = 2 kΩ and C = 1 μF , we have: T = 2 x 103 x 1 x 10-6 = 2 ms, which is the value calculated using the simulator
1.5 Resistor-inductor-capacitor (RLC) transient circuit It is useful to simulate another circuit to make the reader familiar with various options and features of LTspice. In this example, we will analyze the transient response of an RLC circuit when a step input is applied. Drawing the schematic: • Figure 1.10 shows the schematic where a 100 Ω resistor (R1) is connected in series with a 2 mH inductor (L1) and a 2 nF capacitor (C1) and a step voltage of 5 V (V1) is applied to the circuit.
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
Figure 1.10 The schematic Simulation: • Click Run/pause and select Transient. • Set the Stop time to 150u • Click to Skip initial operating point solution (Figure 1.11)
Figure 1.11 Transient mode settings • Click OK. You should see an empty graph. Place the voltage probe at the output point (VC). The time response of the voltage across the capacitor will be displayed. We can insert a title for the graph. Click right on the graph and then select Notes & Annotations -> Text and enter the text Voltage across the capacitor and set its colour to red. Figure 1.12 shows the final graph. The response have oscillatory behaviour, which is called underdamped.
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Practical MOSFET Electronics
Figure 1.12 Voltage across the capacitor The theory The step response of an RLC circuit depends on the damping ratio ξ: ξ>1 ξ=1 ξ<1
is overdamped case is critically damped case is underdamped case
The damping ratio is given by:
In Figure 1.10, ξ = 0.05 and therefore we have an underdamped case with oscillations. The unit step time response of an RLC circuit is given by the formula: v(t) = 1 + e-ξwnt (cos wdt + θ) Where, wn is the undamped natural frequency of oscillation, and is the damped natural frequency. In our example, the undamped natural frequency is given by:
and,
Calculating the damped frequency from the waveform There are several ways that we can calculate the frequency of a waveform in LTspice. Here, we will use two cursors. The steps are:
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
• Right click the title V(vc) at the top of the waveform to open up the Expression Editor window. Select 1st and 2nd as the Attached Cursor (Figure 1.13) and click OK.
Figure 1.13 Select 1st and 2nd cursor • You should see dashed vertical and horizontal lines in the middle of the graph. Place the mouse pointer on this line and number 1 will be displayed. Move number 1 to the first peak of the waveform. • Now go back to the line in the middle and you should see number 2 displayed. Move number 2 to the second peak of the waveform (Figure 1.14)
Figure 1.14 Mark the peaks of the first two waveforms • You should see the waveform details at the bottom right-hand side of the screen where the horizontal and vertical points of the two peaks are displayed. Also, the frequency of the waveform is displayed as 79.692 kHz as shown in Figure 1.15.
Figure 1.15 The frequency is 79.692 kHz
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Practical MOSFET Electronics
Clearly, both the theoretical results and the results obtained from the simulation agree with each other. Fourier spectrum The Fourier spectrum (FFT) of the waveform can be displayed as follows: • Display the underdamped graph as in Figure 1.12 • Right click on the graph and select View -> FFT • Select the output voltage V(vc) and click OK (Figure 1.16)
Figure 1.16 FFT parameters • Figure 1.17 shows the FFT of the output signal. Notice the peak at 79.360 kHz which is the fundamental frequency
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
Figure 1.17 FFT of the output signal Multiple displays As an example, we can display the current through the resistor in another graph. The steps are: • Right click on the waveform and select Add Plot Pane Above. You should see an empty box on top of the main graph • Place a current probe by placing the cursor on top of the resistor and click the mouse. You should see the resistor current displayed on the top pane • Write titles for the two graphs by right clicking on the graphs and selecting Notes & Annotations -> Text. • Figure 1.18 shows the final graphs.
Figure 1.18 Final graphs Simulator settings There are many options that the user can select to configure the simulator. Normally, the default options provided should be fine for all types of simulations. Click on the settings menu (a gear shaped icon at the top left part of the screen) and you can see the available options. You are however advised not to change any options at this stage. Online help The Help menu provides several menu options. There are help options on using the LTspice, help on keyboard shortcuts, support on EngineerZone, link to Analog Devices web site, LTspice update check, and display of the version of LTspice.
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Practical MOSFET Electronics
1.6 Semiconductor diode (P-N junction) fundamentals The semiconductor diode is one of the most fundamental electronic devices and serves as the building block for many modern electronic components. It is primarily formed by joining two differently doped semiconductor materials, creating what is known as a P–N junction. The diode allows electric current to flow predominantly in one direction while restricting current flow in the opposite direction.
1.6.1. Semiconductor Basics Intrinsic semiconductors Pure semiconductor materials such as silicon (Si) and germanium (Ge) are known as intrinsic semiconductors. Their electrical conductivity lies between that of conductors and insulators. The atomic structure of silicon consists of four valence electrons that participate in covalent bonding with neighbouring atoms. At absolute zero, all electrons remain bound within these covalent bonds, resulting in no free charge carriers. As temperature increases, some covalent bonds break, generating: • Free electrons in the conduction band • Holes in the valence band An electron-hole pair is therefore created whenever sufficient thermal energy is supplied. Energy bands In semiconductor physics, electron energies are grouped into bands: • Valence Band (VB): Contains bound electrons. • Conduction Band (CB): Contains free electrons capable of conduction. • Forbidden Energy Gap (Band Gap): Energy difference between the conduction and valence bands. For silicon:
The conductivity of a semiconductor depends strongly on the concentration of free charge carriers. Extrinsic semiconductors The conductivity of intrinsic semiconductors is relatively low. To improve conductivity, controlled impurities are introduced through a process called doping. N-Type semiconductor N-type material is produced by adding pentavalent impurities such as: • Phosphorus (P) • Arsenic (As) • Antimony (Sb)
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Chapter 1 • Semiconductor Fundamentals and Introduction to LTspice
These atoms possess five valence electrons. Four electrons participate in covalent bonding, while the fifth electron becomes weakly bound and can easily become a free electron. Characteristics: • Majority carriers: Electrons • Minority carriers: Holes P-Type semiconductor P-type material is formed by adding trivalent impurities such as: • Boron (B) • Aluminium (Al) • Gallium (Ga) These atoms possess three valence electrons, creating a deficiency of one electron in the crystal lattice. This deficiency behaves as a positive charge carrier known as a hole. Characteristics: • Majority carriers: Holes • Minority carriers: Electrons Formation of the P–N junction When P-type and N-type materials are joined together, a P–N junction is formed. Initially: • The N-region contains a high concentration of electrons. • The P-region contains a high concentration of holes. Due to concentration gradients: • Electrons diffuse from N to P. • Holes diffuse from P to N. When electrons and holes meet, they recombine. As recombination continues: • Positive donor ions remain uncovered in the N-region. • Negative acceptor ions remain uncovered in the P-region. These fixed ions create a region depleted of mobile charge carriers called the depletion region.
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Practical MOSFET Electronics
Index A Active region Add plot pane Alarm system Average voltage B Barrier potential BC337 Biasing MOSFET BJT Bode plot Brushed DC motor BS170 BS250 C Carrier mobility Channel length Channel width Class A amplifier Class AB amplifier Class B amplifier Class C amplifier Class D amplifier Clipping CMOS technology Common drain amplifier Common emitter Common gate amplifier Common source amplifier Conduction band Current controlled device Cutoff region D Dark sensor DCA75 DC Buck converter DC Boost converter DC sweep Depletion region Depletion type Diode clamping
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42 25 158 81
28 45 109 38 115 82, 85 62 64
98 98 98 191, 196 192, 202 191 193 192, 208 195 54 120 45 120 118 26 53 41
64 52 167, 178 185 43 27 56 934
Diode model Driving an LED Duty cycle
30 144 80
E E-MOSFET Emitter bypass capacitor Enhancement type Expression editor Extrinsic semiconductor
58 205 56 43 26
F FFT Flyback diode Forbidden band Forward bias Forward region Fourier spectrum Free electrons Full wave rectifier
24 90 26 29 30 24 26 35
H Hbridge Heat dissipation Heatsink design Help Holes
92 195 71 25 26
I Input coupling capacitor Intrinsic semiconductor IRFZ44N IRLZ44N
205 26 72
J Junction temperature
72
L LDR LM35DZ Load line Logic gates Lossless conversion Loudspeaker load
64 69 51 150 168 195
Index
M Metal gate MOSFET amplifier MOSFET AND gate MOSFET crystal oscillator MOSFET Hartley oscillator MOSFET astable multivibrator MOSFET Colpitts oscillator MOSFET cutoff region MOSFET drain current MOSFET NAND gate MOSFET NOR gate MOSFET NOT gate MOSFET OR gate MOSFET phase shift oscillator MOSFET Pierce oscillator MOSFET input resistance MOSFET linear region MOSFET model MOSFET operating region MOSFET output resistance MOSFET saturation region MOSFET triode region MOSFET voltage gain Motor speed control Move mode Multiple display Multistage amplifier
56 106 151 145 132 122 126 59 107 150 151 150 152 138 145 106 60 106 59 107 61 60 107 89 17 25 117
N N-channel MOSFET NDP6020P NE555 NE555 online calculator NPN Notes & annotations
56 91 169 174 38 20
O Oxide insulator
56
P Passive infrared sensor p-channel MOSFET PIR sensor Plot pane PNP
77 57 76 25 38
Power calculation Powere dissipation PWM PWM frequency
203 198 79 83
Q Q point
51
R RC transient Reed switch Reflected load Reverse bias NEE555 reverse calculator Reverse region
16 66 196 29 175 30
S Safety box Saturation region Substrate
74 42 56
T Temperature control Thermal resistance Tilt switch Touch controller Transconductance Transfer curve Transformer TTP223
68 72 74 75 97 101 199 75
V Valence band Voltage source
26 17
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Practical MOSFET Electronics Theory, LTspice Simulation, and Hands-On Projects MOSFETs are essential components in modern electronics, used in switching, amplification, motor control, power conversion, digital logic, and audio circuits. This book offers a practical introduction to MOSFET technology, combining clear explanations with LTspice simulations and hands-on projects. Starting with semiconductor fundamentals, you will learn how MOSFETs operate, how they compare with BJTs, and how to apply them in real circuits. The book then progresses from basic switching applications to more advanced designs. You will learn how to:
> Understand N-channel and P-channel MOSFET operation > Work with cutoff, triode, and saturation regions > Simulate and analyze circuits using LTspice > Build switching circuits for LEDs, relays, buzzers, sensors, and motors
> Create sensor circuits for light, temperature, touch, tilt, reed switches, and PIR motion detection
> Control motors and fans using PWM and H-bridge circuits > Design MOSFET small-signal amplifiers > Build astable, Colpitts, Hartley, phase-shift, and Pierce oscillators > Experiment with MOSFET digital logic > Explore buck and boost DC-DC converters > Understand the basics of MOSFET audio power amplifiers Written for engineers, students, and experienced makers, this book connects theory with simulation and practical construction, giving you the knowledge and experience to design and experiment with MOSFET circuits with confidence.
Prof. Dr. Dogan Ibrahim has a BSc degree in Electronic Engineering, an MSc degree in Automatic Control Engineering, and a PhD degree in Digital Signal Processing. He worked for several industrial organizations before he returned to academic life. Prof Ibrahim is the author of over 120 technical books and published over 200 technical articles on microcontrollers, microprocessors, and related fields. He is a chartered electrical engineer and a Fellow of the Institution of Engineering and Technology. He is a certified Arduino professional.
Elektor International Media www.elektor.com