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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
End User License Agreement
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:
1 Electrical and electronic devices work because of an electric current.
What is an electric current?
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.
Write at least three ways an electron flow (or current) can be generated.
The following is a list of the most common ways to generate current:
Less common methods to generate an electric current include the following:
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 that contains an arrowhead pointing in the direction of conventional current flow.
4 Ohm's law states the fundamental relationship between voltage, current, and resistance.
What is the algebraic formula for Ohm's law? _____
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.
What is the voltage for each combination of resistance and current values?
V = _____
V = _____
V = _____
V = _____
6 You can rearrange Ohm's law to calculate current values.
What is the current for each combination of voltage and resistance values?
I = _____
I = _____
I = _____
I = _____
7 You can rearrange Ohm's law to calculate resistance values.
What is the resistance for each combination of voltage and current values?
R = _____
R = _____
R = _____
R = _____
8 Work through these examples. In each case, two factors are given and you must find the third.
What are the missing values?
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.
9 You can connect resistors in series. Figure 1.3 shows two resistors in series.
What is their total resistance? _____
The total resistance is often called the equivalent series resistance and is denoted as Req.
10 You can connect resistors in parallel, as shown in Figure 1.4.
What is the total resistance here? _____
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.
What is the formula for three resistors in parallel? _____
You often see this formula in the following form:
12 In the following exercises, two resistors are connected in parallel.
What is the total or equivalent resistance?
RT = _____
RT = _____
RT = _____
RT is always smaller than the smallest of the resistors in parallel.
13 When current flows through a resistor, it dissipates power, usually in the form of heat. Power is expressed in terms of watts.
What is the formula for power? _____
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.
What is the power dissipated by a resistor for the following voltage and current values?
P = _____
P = _____
P = _____
15 The second formula shown in problem 13 allows power to be calculated when only the current and resistance are known.
What is the power dissipated by a resistor given the following resistance and current values?
P = _____
P = _____
P = _____
P = _____
16 Resistors used in electronics generally are manufactured in standard values with regard to resistance and power rating. Appendix D shows a table of standard resistance values for 0.25- and 0.05-watt resistors. Quite often, when a certain resistance value is needed in a circuit, you must choose the closest standard value. This is the case in several examples in this book.
You must also choose a resistor with the power rating in mind. Never place a resistor in a circuit that requires that resistor to dissipate more power than its rating specifies.
If standard power ratings for carbon film resistors are 1/8, 1/4, 1/2, 1, and 2 watts, what power ratings should be selected for the resistors that were used for the calculations in problem 15?
Most electronics circuits use low-power carbon film resistors. For higher-power levels (such as the 5-watt requirement in question A), other types of resistors are available.
17 Although currents much larger than 1 ampere are used in heavy industrial equipment, in most electronic circuits, only fractions of an ampere are required.
18 In electronics, the values of resistance normally encountered are quite high. Often, thousands of ohms and occasionally even millions of ohms are used.
19 The following exercise is typical of many performed in transistor circuits. In this example, 6 volts is applied across a resistor, and 5 mA of current is required to flow through the resistor.
What value of resistance must be used and what power will it dissipate?
R = _____ P = _____
20 Now, try these two simple examples.
What is the missing value?
21 The voltage drop across a resistor and the current flowing through it can be plotted on a simple graph. This graph is called a V-I curve.
Consider a simple circuit in which a battery is connected across a 1 kΩ resistor.
22 Plot the points of battery voltage and current flow from problem 21 on the graph shown in Figure 1.5, and connect them together.
What would the slope of this line be equal to? _____
You should have drawn a straight line, as in the graph shown in Figure 1.6.
Sometimes you need to calculate the slope of the line on a graph. To do this, pick two points and call them A and B.
The slope can be calculated with the following formula:
In other words, the slope of the line is equal to the resistance.
Later, you learn about V-I curves for other components. They have several uses, and often they are not straight lines.
23 The circuit shown in Figure 1.7 is called a voltage divider. It is the basis for many important theoretical and practical ideas you encounter throughout the entire field of electronics.
The object of this circuit is to create an output voltage (V0) that you can control based upon the two resistors and the input voltage. V0 is also the voltage drop across R2.
What is the formula for V0? _____
R1 + R2 = RT, the total resistance of the circuit.
24 A simple example can demonstrate the use of this formula.
For the circuit shown in Figure 1.8, what is V0? _____
25 Now, try these problems.
What is the output voltage for each combination of supply voltage and resistance?
V0 = _____
V0 = _____
V0 = _____
V0 = _____
26 The output voltage from the voltage divider is always less than the applied voltage. Voltage dividers are often used to apply specific voltages to different components in a circuit. Use the voltage divider equation to answer the following questions.
A convenient way to create a prototype of an electronic circuit to verify that it works is to build it on a breadboard. You can use breadboards to build the circuits used in the projects later in this book. As shown in the following figure, a breadboard is a sheet of plastic with several contact holes. You use these holes to connect electronic components in a circuit. After you verify that a circuit works with this method, you can then create a permanent circuit using soldered connections.
Breadboards contain metal strips arranged in a pattern under the contact holes, which are used to connect groups of contacts together. Each group of five contact holes in a vertical line (such as the group circled in the figure) is connected by these metal strips. Any components plugged into one of these five contact holes are, therefore, electrically connected.
Each row of contact holes marked by a “+” or “−” are connected by these metal strips. The rows marked “+” are connected to the positive terminal of the battery or power supply and are referred to as the +V bus. The rows marked “−” are connected to the negative terminal of the battery or power supply and are referred to as the ground bus. The 1V buses and ground buses running along the top and bottom of the breadboard make it easy to connect any component in a circuit with a short piece of wire called a jumper wire. Jumper wires are typically made of 22-gauge solid wire with approximately 1/4 inch of insulation stripped off each end.
The following figure shows a voltage divider circuit assembled on a breadboard. One end of R1 is inserted into a group of contact holes that is also connected by a jumper wire to the 1V bus. The other end of R1 is inserted into the same group of contact holes that contains one end of R2. The other end of R2 is inserted into a group of contact holes that is also connected by a jumper wire to the ground bus. In this example, a 1.5 kΩ resistor was used for R1, and a 5.1 kΩ resistor was used for R2.
A terminal block is used to connect the battery pack to the breadboard because the wires supplied with battery packs (which are stranded wire) can't be inserted directly into breadboard contact holes. The red wire from a battery pack is attached to the side of the terminal block that is inserted into a group of contact holes, which is also connected by a jumper wire to the 1V bus. The black wire from a battery pack is attached to the side of the terminal block that is inserted into a group of contact holes, which is also connected by a jumper wire to the ground bus.
To connect the output voltage, Vo, to a multimeter or a downstream circuit, two additional connections are needed. One end of a jumper wire is inserted in the same group of contact holes that contain both R1 and R2 to supply Vo. One end of another jumper wire is inserted in a contact hole in the ground bus to provide an electrical contact to the negative side of the battery. When connecting test equipment to the breadboard, you should use a 20-gauge jumper wire because sometimes the 22-gauge wire is pulled out of the board when attaching test probes.
27 In the circuit shown in Figure 1.9, the current splits or divides between the two resistors that are connected in parallel.
IT splits into the individual currents I1 and I2, and then these recombine to form IT.
Which of the following relationships are valid for this circuit?
All of them are valid.
28 When solving current divider problems, follow these steps:
I1/I2 = R2/R1
The values of two resistors in parallel and the total current flowing through the circuit are shown in Figure 1.10. What is the current through each individual resistor?
Work through the steps as shown here:
29 Now, try these problems. In each case, the total current and the two resistors are given. Find I1 and I2.
Question C is actually a demonstration of Kirchhoff's Current Law (KCL). Simply stated, this law says that the total current entering a junction in a circuit must equal the sum of the currents leaving that junction. This law is also used on numerous occasions in later chapters. KVL and KCL together form the basis for many techniques and methods of analysis that are used in the application of circuit analysis.
Also, the current through a resistor is inversely proportional to the resistor's value. Therefore, if one resistor is larger than another in a parallel circuit, the current flowing through the higher value resistor is the smaller of the two. Check your results for this problem to verify this.
30 You can also use the following equation to calculate the current flowing through a resistor in a two-branch parallel circuit:
Write the equation for the current I2. _____
Check the answers for the previous problem using these equations.
The current through one branch of a two-branch circuit is equal to the total current times the resistance of the opposite branch, divided by the sum of the resistances of both branches. This is an easy formula to remember.
A multimeter is a must-have testing device for anyone's electronics toolkit. A multimeter is aptly named because it can be used to measure multiple parameters. Using a multimeter, you can measure current, voltage, and resistance by setting the rotary switch on the multimeter to the parameter you want to measure, and connecting each mulitmeter probe to a wire in a circuit. The following figure shows a multimeter connected to a voltage divider circuit to measure voltage. Following are the details of how you take each of these measurements.
Voltage
To measure the voltage in the circuit shown in the figure, at the connection between R1 and R2, use jumper wire to connect the red probe of a multimeter to the row of contact holes containing leads from both R1 and R2. Use another jumper wire to connect the black probe of the multimeter to the ground bus. Set the rotary switch on the multimeter to measure voltage, and it returns the results.
Current
The following figure shows how you connect a multimeter to a voltage divider circuit to measure current. Connect a multimeter in series with components in the circuit, and set the rotary switch to the appropriate ampere range, depending upon the magnitude of the expected current. To connect the multimeter in series with R1 and R2, use a jumper wire to connect the +V bus to the red lead of a multimeter, and another jumper wire to connect the black lead of the multimeter to R1. These connections force the current flowing through the circuit to flow through the multimeter.
Resistance
You typically use the resistance setting on a multimeter to check the resistance of individual components. For example, in measuring the resistance of R2 before assembling the circuit shown in the previous figure, the result was 5.0 kΩ, slightly off the nominal 5.1 kΩ stated value.
You can also use a multimeter to measure the resistance of a component in a circuit. A multimeter measures resistance by applying a small current through the components being tested, and measuring the voltage drop. Therefore, to prevent false readings, you should disconnect the battery pack or power supply from the circuit before using the multimeter.
31 A mechanical switch is a device that completes or breaks a circuit. The most familiar use is that of applying power to turn a device on or off. A switch can also permit a signal to pass from one place to another, prevent its passage, or route a signal to one of several places.
In this book, you work with two types of switches. The first is the simple on-off switch, also called a single pole single throw switch. The second is the single pole double throw switch. Figure 1.11 shows the circuit symbols for each.
Keep in mind the following two important facts about switches:
The circuit shown in Figure 1.12 includes a closed switch.
32 The circuit shown in Figure 1.13 includes an open switch.
33 The circuit shown in Figure 1.14 includes a single pole double throw switch. The position of the switch determines whether lamp A or lamp B is lit.
34 Capacitors are used extensively in electronics. They are used in both alternating current (AC) and DC circuits. Their main use in DC electronics is to become charged, hold the charge, and, at a specific time, release the charge.
The capacitor shown in Figure 1.15 charges when the switch is closed.
To what final voltage will the capacitor charge? _____
It will charge up to 10 volts. It will charge up to the voltage that would appear across an open circuit located at the same place where the capacitor is located.
35 How long does it take to reach this voltage? This is an important question with many practical applications. To find the answer you must know the time constant (τ) (Greek letter tau) of the circuit.
36 The capacitor does not begin charging until the switch is closed. When a capacitor is uncharged or discharged, it has the same voltage on both plates.
37 The capacitor charging graph in Figure 1.16 shows how many time constants a voltage must be applied to a capacitor before it reaches a given percentage of the applied voltage.
38 In the following examples, a resistor and a capacitor are in series. Calculate the time constant, how long it takes the capacitor to fully charge, and the voltage level after one time constant if a 10-volt battery is used.
39 The circuit shown in Figure 1.17 uses a double pole switch to create a discharge path for the capacitor.
40 Suppose that the switch shown in Figure 1.17 is moved back to position X after the capacitor is fully charged.
41 Capacitors can be connected in parallel, as shown in Figure 1.18.
In other words, the total capacitance is found by simple addition of the capacitor values.
42 Capacitors can be placed in series, as shown in Figure 1.19.
43 In each of these examples, the capacitors are placed in series. Find the total capacitance.
The few simple principles reviewed in this chapter are those you need to begin the study of electronics. Following is a summary of these principles:
The following problems and questions test your understanding of the basic principles presented in this chapter. You need a separate sheet of paper for your calculations. Compare your answers with the answers provided following the test. You can work many of the problems in more than one way.
Questions 1–5 use the circuit shown in Figure 1.20. Find the unknown values indicated using the values given.
RT = _____ , I = _____
V1 = _____ , V2 = _____ , VS = _____
V1 = _____ , V2 = _____
R2 = _____
P1 = _____ , P2 = _____ , PT = _____
Questions 6–8 use the circuit shown in Figure 1.21. Again, find the unknowns using the given values.
RT = _____ , I = _____
I1 = _____ , I2 = _____
R2 = _____ , P1 = _____
IMAX = _____
C = _____
VC = _____
T = _____
R1 = _____
VC = _____, T = _____
τ = _____ , T = _____
C1 = 8 μF; C2 = 4 μF; C3 = 12 μF.
CT = _____
CT = _____
CT = _____
If your answers do not agree with those provided here, review the problems indicated in parentheses before you go to Chapter 2, “The Diode.” If you still feel uncertain about these concepts, go to a website such as www.BuildingGadgets.com and work through DC tutorials listed there.
It is assumed that Ohm's law is well known, so problem 4 will not be referenced.
1. | RT = 48 ohms, I = 0.5 ampere | (problem 9) |
2. | V1 = 5 volts, V2 = 15 volts, VS = 20 volts | (problems 23 and 26) |
3. | V1 = 14.4 volts, V2 = 9.6 volts | (problems 23 and 26) |
4. | R2 = 120 ohms | (problems 9 and 23) |
5. | P1 = 3 watts, P2 = 9 watts, PT = 12 watts | (problems 9 and 13) |
6. | RT = 4 kΩ, I = 5 mA | (problem 10) |
7. | I1 = 1.5 amperes, I2 = 0.5 ampere | (problems 28 and 29) |
8. | R2 = 200 ohms, P1 = 2.88 watts | (problems 10 and 13) |
9. | IMAX = 33.7 mA | (problems 13, 15, and 16) |
10A. | C = 0.06 μF | (problems 34 and 35) |
10B. | VC = 1.9 volts | (problem 35) |
10C. | T = 300 μsec | (problems 34–38) |
11A. | R1 = 30 kΩ | (problems 33, 39, and 40) |
11B. | VC = 15 V, T = 24 ms | (problem 35) |
11C. | τ = 1.6 ms, T = 8.0 ms | (problems 39–40) |
12A. | CT = 24 μF | (problems 41 and 42) |
12B. | CT = 2.18 μF | (problem 42) |
12C. | CT = 5.33 μF | (problems 42–43) |
Chapter 2
The Diode
The main characteristic of a diode is that it conducts electricity in one direction only. Historically, the first vacuum tube was a diode; it was also known as a rectifier. The modern diode is a semiconductor device. It is used in all applications where the older vacuum tube diode was used, but it has the advantages of being much smaller, easier to use, and less expensive.
A semiconductor is a crystalline material that, depending on the conditions, can act as a conductor (allowing the flow of electric current) or an insulator (preventing the flow of electric current). Techniques have been developed to customize the electrical properties of adjacent regions of semiconductor crystals, which allow the manufacture of small diodes, as well as transistors and integrated circuits.
When you complete this chapter, you can do the following:
1 dopingN typeP type.holes.