by Earl Boysen
Table of Contents
Chapter 1: DC Review and Pre-Test
Current Flow
Ohm's Law
Resistors in Series
Resistors in Parallel
Power
Small Currents
The Graph of Resistance
The Voltage Divider
The Current Divider
Switches
Capacitors in a DC Circuit
Summary
DC Pre-Test
Chapter 2: The Diode
Understanding Diodes
Diode Breakdown
The Zener Diode
Summary
Self-Test
Chapter 3: Introduction to the Transistor
Understanding Transistors
The Junction Field Effect Transistor (JFET)
Summary
Self-Test
Chapter 4: The Transistor Switch
Turning the Transistor On
Turning Off the Transistor
Why Transistors Are Used as Switches
The Three-Transistor Switch
Alternative Base Switching
Switching the JFET
Summary
Self-Test
Chapter 5: AC Pre-Test and Review
The Generator
Resistors in AC Circuits
Capacitors in AC Circuits
The Inductor in an AC Circuit
Resonance
Summary
Self-Test
Chapter 6: Filters
Capacitors in AC Circuits
Capacitors and Resistors in Series
Phase Shift of an RC Circuit
Resistor and Capacitor in Parallel
Inductors in AC Circuits
Phase Shift for an RL Circuit
Summary
Self-Test
Chapter 7: Resonant Circuits
The Capacitor and Inductor in Series
The Output Curve
Introduction to Oscillators
Summary
Self-Test
Chapter 8: Transistor Amplifiers
Working with Transistor Amplifiers
A Stable Amplifier
Biasing
The Emitter Follower
Analyzing an Amplifier
The JFET as an Amplifier
The Operational Amplifier
Summary
Self-Test
Chapter 9: Oscillators
Understanding Oscillators
Feedback
The Colpitts Oscillator
The Hartley Oscillator
The Armstrong Oscillator
Practical Oscillator Design
Simple Oscillator Design Procedure
Oscillator Troubleshooting Checklist
Summary and Applications
Self-Test
Chapter 10: The Transformer
Transformer Basics
Transformers in Communications Circuits
Summary and Applications
Self-Test
Answers to Self-Test
Chapter 11: Power Supply Circuits
Diodes in AC Circuits Produce Pulsating DC
Level DC (Smoothing Pulsating DC)
Summary
Self-Test
Chapter 12: Conclusion and Final Self-Test
Conclusion
Final Self-Test
Appendix A: Glossary
Appendix B: List of Symbols and Abbreviations
Appendix C: Powers of Ten and Engineering Prefixes
Appendix D: Standard Composition Resistor Values
Appendix E: Supplemental Resources
Web Sites
Books
Magazines
Suppliers
Appendix F: Equation Reference
Appendix G: Schematic Symbols Used in This Book
Introduction
What This Book Teaches
How This Book Is Organized
Conventions Used in This Book
How to Use This Book
Chapter 1
DC Review and Pre-Test
Electronics cannot be studied without first understanding the basics of electricity. This chapter is a review and pre-test on those aspects of direct current (DC) that apply to electronics. By no means does it cover the whole DC theory, but merely those topics that are essential to simple electronics.
This chapter reviews the following:
Current flow
Potential or voltage difference
Ohm's law
Resistors in series and parallel
Power
Small currents
Resistance graphs
Kirchhoff's Voltage Law
Kirchhoff's Current Law
Voltage and current dividers
Switches
Capacitor charging and discharging
Capacitors in series and parallel
Current Flow
1 Electrical and electronic devices work because of an electric current.
Question
What is an electric current?
Answer
An electric current is a flow of electric charge. The electric charge usually consists of negatively charged electrons. However, in semiconductors, there are also positive charge carriers called holes.
2 There are several methods that can be used to generate an electric current.
Question
Write at least three ways an electron flow (or current) can be generated.
Answer
The following is a list of the most common ways to generate current:
Magnetically—This includes the induction of electrons in a wire rotating within a magnetic field. An example of this would be generators turned by water, wind, or steam, or the fan belt in a car.
Chemically—This involves the electrochemical generation of electrons by reactions between chemicals and electrodes (as in batteries).
Photovoltaic generation of electrons—This occurs when light strikes semiconductor crystals (as in solar cells).
Less common methods to generate an electric current include the following:
Thermal generation—This uses temperature differences between thermocouple junctions. Thermal generation is used in generators on spacecrafts that are fueled by radioactive material.
Electrochemical reaction—This occurs between hydrogen, oxygen, and electrodes (fuel cells).
Piezoelectrical—This involves mechanical deformation of piezoelectric substances. For example, piezoelectric material in the heels of shoes power LEDs that light up when you walk.
3 Most of the simple examples in this book contain a battery as the voltage source. As such, the source provides a potential difference to a circuit that enables a current to flow. An electric current is a flow of electric charge. In the case of a battery, electrons are the electric charge, and they flow from the terminal that has an excess number of electrons to the terminal that has a deficiency of electrons. This flow takes place in any complete circuit that is connected to battery terminals. It is this difference in the charge that creates the potential difference in the battery. The electrons try to balance the difference.
Because electrons have a negative charge, they actually flow from the negative terminal and return to the positive terminal. This direction of flow is called electron flow. Most books, however, use current flow, which is in the opposite direction. It is referred to as conventional current flow, or simply current flow. In this book, the term conventional current flow is used in all circuits.
Later in this book, you see that many semiconductor devices have a symbol t
hat contains an arrowhead pointing in the direction of conventional current flow.
Questions
A. Draw arrows to show the current flow in Figure 1.1. The symbol for the battery shows its polarity.
Figure 1.1
B. What indicates that a potential difference is present? __________
C. What does the potential difference cause? __________
D. What will happen if the battery is reversed? __________
Answers
A. See Figure 1.2.
Figure 1.2
B. The battery symbol indicates that a difference of potential (also called voltage) is being supplied to the circuit.
C. Voltage causes current to flow if there is a complete circuit present, as shown in Figure 1.1.
D. The current flows in the opposite direction.
Ohm's Law
4 Ohm's law states the fundamental relationship between voltage, current, and resistance.
Question
What is the algebraic formula for Ohm's law? _____
Answer
This is the most basic equation in electricity, and you should know it well. Some electronics books state Ohm's law as E = IR. E and V are both symbols for voltage. This book uses V to indicate voltage. When V is used after a number in equations and circuit diagrams, it represents volts, the unit of measurement of voltage. Also, in this formula, resistance is the opposition to current flow. Larger resistance results in smaller current for any given voltage.
5 Use Ohm's law to find the answers in this problem.
Questions
What is the voltage for each combination of resistance and current values?
A. R = 20 ohms, I = 0.5 amperes
V = _____
B. R = 560 ohms, I = 0.02 amperes
V = _____
C. R = 1,000 ohms, I = 0.01 amperes
V = _____
D. R = 20 ohms I = 1.5 amperes
V = _____
Answers
A. 10 volts
B. 11.2 volts
C. 10 volts
D. 30 volts
6 You can rearrange Ohm's law to calculate current values.
Questions
What is the current for each combination of voltage and resistance values?
A. V = 1 volt, R = 2 ohms
I = _____
B. V = 2 volts, R = 10 ohms
I = _____
C. V = 10 volts, R = 3 ohms
I = _____
D. V = 120 volts, R = 100 ohms
I = _____
Answers
A. 0.5 amperes
B. 0.2 amperes
C. 3.3 amperes
D. 1.2 amperes
7 You can rearrange Ohm's law to calculate resistance values.
Questions
What is the resistance for each combination of voltage and current values?
A. V = 1 volt, I = 1 ampere
R = _____
B. V = 2 volts, I = 0.5 ampere
R = _____
C. V = 10 volts, I = 3 amperes
R = _____
D. V = 50 volts, I = 20 amperes
R = _____
Answers
A. 1 ohm
B. 4 ohms
C. 3.3 ohms
D. 2.5 ohms
8 Work through these examples. In each case, two factors are given and you must find the third.
Questions
What are the missing values?
A. 12 volts and 10 ohms. Find the current. __________
B. 24 volts and 8 amperes. Find the resistance. __________
C. 5 amperes and 75 ohms. Find the voltage. _____
Answers
A. 1.2 amperes
B. 3 ohms
C. 375 volts
Inside the Resistor
Resistors are used to control the current that flows through a portion of a circuit. You can use Ohm's law to select the value of a resistor that gives you the correct current in a circuit. For a given voltage, the current flowing through a circuit increases when using smaller resistor values and decreases when using larger resistor values.
This resistor value works something like pipes that run water through a plumbing system. For example, to deliver the large water flow required by your water heater, you might use a 1-inch diameter pipe. To connect a bathroom sink to the water supply requires much smaller water flow and, therefore, works with a 1/2-inch pipe. In the same way, smaller resistor values (meaning less resistance) increase current flow, whereas larger resistor values (meaning more resistance) decrease the flow.
Tolerance refers to how precise a stated resistor value is. When you buy fixed resistors (in contrast to variable resistors that are used in some of the projects in this book), they have a particular resistance value. Their tolerance tells you how close to that value their resistance will be. For example, a 1,000-ohm resistor with ± 5 percent tolerance could have a value of anywhere from 950 ohms to 1,050 ohms. A 1,000-ohm resistor with ± 1 percent tolerance (referred to as a precision resistor) could have a value ranging anywhere from 990 ohms to 1,010 ohms. Although you are assured that the resistance of a precision resistor will be close to its stated value, the resistor with ± 1 percent tolerance costs more to manufacture and, therefore, costs you more than twice as much as a resistor with ± 5 percent.
Most electronic circuits are designed to work with resistors with ± 5 percent tolerance. The most commonly used type of resistor with ± 5 percent tolerance is called a carbon film resistor. This term refers to the manufacturing process in which a carbon film is deposited on an insulator. The thickness and width of the carbon film determines the resistance (the thicker the carbon film, the lower the resistance). Carbon film resistors work well in all the projects in this book.
On the other hand, precision resistors contain a metal film deposited on an insulator. The thickness and width of the metal film determines the resistance. These resistors are called metal film resistors and are used in circuits for precision devices such as test instruments.
Resistors are marked with four or five color bands to show the value and tolerance of the resistor, as illustrated in the following figure. The four-band color code is used for most resistors. As shown in the figure, by adding a fifth band, you get a five-band color code. Five-band color codes are used to provide more precise values in precision resistors.
The following table shows the value of each color used in the bands:
By studying this table, you can see how this code works. For example, if a resistor is marked with orange, blue, brown, and gold bands, its nominal resistance value is 360 ohms with a tolerance of ± 5 percent. If a resistor is marked with red, orange, violet, black, and brown, its nominal resistance value is 237 ohms with a tolerance of ± 1 percent.
Resistors in Series
9 You can connect resistors in series. Figure 1.3 shows two resistors in series.
Figure 1.3
Question
What is their total resistance? _____
Answers
The total resistance is often called the equivalent series resistance and is denoted as Req.
Resistors in Parallel
10 You can connect resistors in parallel, as shown in Figure 1.4.
Figure 1.4
Question
What is the total resistance here? _____
Answers
RT is often called the equivalent parallel resistance.
11 The simple formula from problem 10 can be extended to include as many resistors as wanted.
Question
What is the formula for three resistors in parallel? _____
Answers
You often see this formula in the following form:
12 In the following exercises, two resistors are connected in parallel.
Questions
What is the total or equivalent resistance?
A. R1 = 1 ohm, R2 = 1 ohm
RT = _____
B. R1 = 1,000 ohms, R2 = 500 ohms
RT = _____
C. R1 = 3,600 ohms, R2 = 1,800 ohms
RT = _____
Answers
A. 0.5 ohms
B. 333 ohms
C. 1,200 ohms
RT is always smaller than the smallest of the resistors in parallel.
Power
13 When current flows through a resistor, it dissipates power, usually in the form of heat. Power is expressed in terms of watts.
Question
What is the formula for power? _____
Answers
There are three formulas for calculating power:
14 The first formula shown in problem 13 allows power to be calculated when only the voltage and current are known.
Questions
What is the power dissipated by a resistor for the following voltage and current values?
A. V = 10 volts, I = 3 amperes
P = _____
B. V = 100 volts, I = 5 amperes
P = _____
C. V = 120 volts, I = 10 amperes
P = _____
Answers
A. 30 watts.
B. 500 watts, or 0.5 kW. (The abbreviation kW indicates kilowatts.)
C. 1,200 watts, or 1.2 kW.
15 The second formula shown in problem 13 allows power to be calculated when only the current and resistance are known.
Questions
What is the power dissipated by a resistor given the following resistance and current values?
A. R = 20 ohm, I = 0.5 ampere
P = _____
B. R = 560 ohms, I = 0.02 ampere
P = _____
C. V = 1 volt, R = 2 ohms
P = _____
D. V = 2 volt, R = 10 ohms
P = _____
Answers
A. 5 watts
B. 0.224 watts
C. 0.5 watts
D. 0.4 watts