In your study of Electronic Principles, you will be introduced to a variety of elec- tronic semiconductor devices. Each of these devices will have unique properties and characteristics. Your knowledge of how these individual components function is very important. But this is just the beginning.
These electronic devices normally do not function on their own. Instead, with the addition of other electronic components, such as resistors, capacitors, inductors, and other semiconductor devices, they are interconnected to form elec- tronic circuits. These electronic circuits are often categorized into subsets, such as analog circuits and digital circuits, or application specifi c circuits as amplifi - ers, converters, rectifi ers, and so on. While analog circuits operate with infi nitely varying quantities, often referred to as linear electronics, digital circuits gener- ally operate with signal levels found in two distinct states representing logical or numeric values. A basic diode rectifi er circuit, using a transformer, diode, capaci- tor, and resistor, is shown in Fig. 3-20a.
What happens when different types of circuits are connected together?
By combining a variety of circuits, functional blocks can be formed. These blocks, which can be made up of multiple stages, are designed to take a specifi c type of Figure 3-19 The SOT-23 is a three-terminal transistor package commonly used for SM diodes.
0.1 in SCALE SIDE END
TOP PIN 1
PIN 2
PIN 3
MOUNTING LEADS
input signal and produce the desired output. As an example, Fig. 3-20b is an am- plifi er, with two stages, used to increase signal levels from an input of 10 mVp-p to an output of 10 Vp-p.
Can electronic functional blocks be interconnected? Absolutely! This is when the study of electronics becomes so dynamic and diverse. These intercon- nected electronic function blocks are essentially grouped together to create elec- tronic systems. Electronic systems can be found in a variety of areas including automation and industrial control, communications, computer information, secu- rity systems and more. Fig. 3-20c is a block diagram of a basic communications receiver system broken down into functional blocks. This type of diagram is very useful when troubleshooting systems.
In summary, semiconductor components are combined with other com- ponents to form circuits. Circuits can be combined to become functional blocks.
Functional blocks can be interconnected to form electronic systems. To go one step further, electronic systems are often connected to form complex systems.
To help understand how these concepts all work together, this chapter in- troduces a Digital/Analog Trainer System. This trainer is used for building, testing, and prototyping analog and digital circuits. Many of the electronic devices found in following chapters are used in this trainer. Some chapters in this textbook will have end-of-chapter questions referring to this trainer system. This will give you experience seeing how individual electronic components work together and how circuits function together.
The schematic diagram for this trainer system can be found on the Instructor Resources section of Connect for Electronic Principles.
Figure 3-20 (a) Basic diode rectifi er circuit; (b) amplifi er functional block; (c) communication receiver block diagram.
T1
C1 R1 AC
Input
DC Output D1
– + –
+
(a)
Stage 1 Stage 2 Amplifier
10 Vp-p 10 mVp-p
(b)
RF Amplifier Antenna
Speaker Mixer I.F.
Amplifier
Oscillator Regulated
Power Supply Detector Pre-
amplifier
Power Amplifier
(c)
80 Chapter 3
Summary
SEC. 3-1 BASIC IDEAS
A diode is a nonlinear device. The knee voltage, approximately 0.7 V for a silicon diode, is where the for- ward curve turns upward. The bulk resistance is the ohmic resistance of the p and n regions. Diodes have a maximum forward current and a power rating.
SEC. 3-2 THE IDEAL DIODE This is the fi rst approximation of a diode. The equivalent circuit is a switch that closes when forward biased and opens when reverse biased.
SEC. 3-3 THE SECOND APPROXIMATION In this approximation, we visualize a silicon diode as a switch in series with a knee voltage of 0.7 V. If the Thevenin voltage facing the diode is greater than 0.7 V, the switch closes.
SEC. 3-4 THE THIRD APPROXIMATION We seldom use this approximation because bulk resistance is usually small enough to ignore. In this ap- proximation, we visualize the diode as a switch in series with a knee volt- age and a bulk resistance.
SEC. 3-5 TROUBLESHOOTING When you suspect that a diode is the trouble, remove it from the circuit and use an ohmmeter to measure its resistance in each direction. You
should get a high resistance one way and a low resistance the other way, at least 1000:1 ratio. Remember to use a high enough resistance range when testing a diode to avoid possible diode damage. A DMM will display 0.5–0.7 V when a diode is forward biased and an overrange indication when it is reverse biased.
SEC. 3-6 READING A DATA SHEET
Data sheets are useful to a circuit designer and may be useful to a repair technician when selecting a substitute device, which is sometimes required. Diode data sheets from diff erent manufacturers contain similar information, but diff erent symbols are used to indi- cate diff erent operating conditions.
Diode data sheets may list the following: breakdown voltage (VR, VRRM, VRWM, PIV, PRV, BV), maximum forward current
(IF(max), IF(av), I0), forward voltage drop (VF(max), VF), and maximum reverse current (IR(max), IRRM).
SEC. 3-7 HOW TO CALCULATE BULK RESISTANCE You need two points in the forward region of the third approximation.
One point can be 0.7 V with zero current. The second point comes from the data sheet at a large forward current where both a voltage and a current are given.
SEC. 3-8 DC RESISTANCE OF A DIODE
The dc resistance equals the diode voltage divided by the diode cur- rent at some operating point. This resistance is what an ohmmeter will measure. DC resistance has limited application, aside from telling you that it is small in the forward direction and large in the reverse direction.
SEC. 3-9 LOAD LINES
The current and voltage in a diode circuit have to satisfy both the diode curve and Ohm’s law for the load resistor. These are two separate re- quirements that graphically translate to the intersection of the diode curve and the load line.
SEC. 3-10 SURFACE-MOUNT DIODES
Surface-mount diodes are often found on modern electronics circuits boards. These diodes are small, effi - cient, and typically found either as an SM (surface-mount) or an SOT (small outline transistor) case style.
SEC. 3-11 INTRODUCTION TO ELECTRONIC SYSTEMS
Semiconductor components are combined to form circuits. Circuits can be combined to become func- tional blocks. Functional blocks can be interconnected to form electronic systems.
(3-1) Silicon knee voltage:
+ – 0.7 V
VK < 0.7 V
(3-2) Bulk resistance:
P N
RB 5 RP 1 RN
Defi nitions
(3-4) Maximum power dissipation Pmax
Pmax 5 VmaxImax
(3-6) Ignore bulk:
RB RTH LINEAR
CIRCUIT
RB , 0.01RTH
Derivations
(3-3) Diode power dissipation:
PD
PD 5 VDID
(3-5) Third approximation:
RB
VD – + 0.7 V – +
VD 5 0.7 V 1 IDRB
(3-7) Bulk resistance:
V2 V1 I1
I2
RB 5 _______V2 2 V1
I2 2 I1
Self-Test
1. When the graph of current ver- sus voltage is a straight line, the device is referred to as a. Active c. Nonlinear b. Linear d. Passive 2. What kind of device is a
resistor?
a. Unilateral c. Nonlinear b. Linear d. Bipolar 3. What kind of a device is a
diode?
a. Bilateral c. Nonlinear b. Linear d. Unipolar 4. How is a nonconducting diode
biased?
a. Forward c. Poorly b. Inverse d. Reverse 5. When the diode current is
large, the bias is a. Forward b. Inverse c. Poor d. Reverse
6. The knee voltage of a diode is approximately equal to the a. Applied voltage
b. Barrier potential c. Breakdown voltage d. Forward voltage
7. The reverse current consists of minority-carrier current and a. Avalanche current
b. Forward current
c. Surface-leakage current d. Zener current
8. How much voltage is there across the second approxima- tion of a silicon diode when it is forward biased?
a. 0 b. 0.3 V c. 0.7 V d. 1 V
9. How much current is there through the second approxima- tion of a silicon diode when it is reverse biased?
a. 0 b. 1 mA c. 300 mA
d. None of the above
10. How much forward diode volt- age is there with the ideal diode approximation?
a. 0 b. 0.7 V
c. More than 0.7 V d. 1 V
11. The bulk resistance of a 1N4001 is
a. 0 b. 0.23 V c. 10 V d. 1 kV
12. If the bulk resistance is zero, the graph above the knee becomes
a. Horizontal b. Vertical c. Tilted at 45°
d. None of the above
13. The ideal diode is usually adequate when
a. Troubleshooting
b. Doing precise calculations c. The source voltage is low d. The load resistance is low 14. The second approximation
works well when a. Troubleshooting b. Load resistance is high c. Source voltage is high d. All of the above
15. The only time you have to use the third approximation is when
a. Load resistance is low b. Source voltage is high c. Troubleshooting d. None of the above
16. How much load
current is there in Fig. 3-21 with the ideal diode?
a. 0 b. 11.3 mA c. 12 mA d. 25 mA
VS 12 V
RL 1 kΩ –
+
Figure 3-21
82 Chapter 3
17. How much load
current is there in Fig. 3-21 with the second approximation?
a. 0 b. 11.3 mA c. 12 mA d. 25 mA
18. How much load
current is there in Fig. 3-21 with the third approximation?
a. 0 b. 11.3 mA c. 12 mA d. 25 mA
19. If the diode is open in Fig. 3-21, the load voltage is a. 0
b. 11.3 V c. 20 V d. 215 V
20. If the resistor is ungrounded in Fig. 3-21, the voltage measured with a DMM between the top of the resistor and ground is closest to a. 0 c. 20 V b. 12 V d. 215 V
21. The load voltage measures 12 V in Fig. 3-21. The trouble may be
a. A shorted diode b. An open diode c. An open load resistor d. Too much supply voltage 22. Using the third approximation
in Fig. 3-21, how low must RL
be before the diode’s bulk re- sistance must be considered?
a. 1 V c. 23 V b. 10 V d. 100 V
SEC. 3-1 BASIC IDEAS
3-1 A diode is in series with 220 V. If the voltage across the resistor is 6 V, what is the current through the diode?
3-2 A diode has a voltage of 0.7 V and a current of 100 mA. What is the diode power?
3-3 Two diodes are in series. The fi rst diode has a volt- age of 0.75 V and the second has a voltage of 0.8 V. If the current through the fi rst diode is 400 mA, what is the current through the second diode?
SEC. 3-2 THE IDEAL DIODE
3-4 In Fig. 3-22a, calculate the load current, load voltage, load power, diode power, and total power.
3-5 If the resistor is doubled in Fig. 3-22a, what is the load current?
Problems
3-6 In Fig. 3-22b, calculate the load current, load volt- age, load power, diode power, and total power.
3-7 If the resistor is doubled in Fig. 3-22b, what is the load current?
3-8 If the diode polarity is reversed in Fig. 3-22b, what is the diode current? The diode voltage?
SEC. 3-3 THE SECOND APPROXIMATION 3-9 In Fig. 3-22a, calculate the load current, load volt-
age, load power, diode power, and total power.
3-10 If the resistor is doubled in Fig. 3-22a, what is the load current?
3-11 In Fig. 3-22b, calculate the load current, load volt- age, load power, diode power, and total power.
3-12 If the resistor is doubled in Fig. 3-22b, what is the load current?
3-13 If the diode polarity is reversed in Fig. 3-22b, what is the diode current? The diode voltage?
SEC. 3-4 THE THIRD APPROXIMATION 3-14 In Fig. 3-22a, calculate the load current, load
voltage, load power, diode power, and total power. (RB 5 0.23 V)
3-15 If the resistor is doubled in Fig. 3-22a, what is the load current? (RB 5 0.23 V)
3-16 In Fig. 3-22b, calculate the load current, load voltage, load power, diode power, and total power. (RB 5 0.23 V)
3-17 If the resistor is doubled in Fig. 3-22b, what is the load current? (RB 5 0.23 V)
3-18 If the diode polarity is reversed in Fig. 3-22b, what is the diode current? The diode voltage?
RL 1 kΩ
(a)
(b) VS
12 V VS 20 V
RL 470 Ω –
+
– +
Figure 3-22
SEC. 3-5 TROUBLESHOOTING
3-19 Suppose the voltage across the diode of Fig. 3-23a is 5 V. Is the diode open or shorted?
3-21 You measure 0 V across the diode of Fig. 3-23a.
Next you check the source voltage and it reads 15 V with respect to ground. What is wrong with the circuit?
3-22 In Fig. 3-23b, you measure a potential of 13 V at the junction of R1 and R2. (Remember, potentials are always with respect to ground.) Next you measure 0 V at the junction of the diode and the 5-kV resistor. Name some possible troubles.
3-23 The forward and reverse DMM diode test reading is 0.7 V and 1.8 V. Is this diode good?
SEC. 3-6 READING A DATA SHEET
3-24 Which diode would you select in the 1N4000 se- ries if it has to withstand a peak repetitive reverse voltage of 300 V?
3-25 The data sheet shows a band on one end of the diode. What is the name of this band? Does the diode arrow of the schematic symbol point toward or away from this band?
3-26 Boiling water has a temperature of 100°C. If you drop a 1N4001 into a pot of boiling water, will it be destroyed or not? Explain your answer.
100 kΩ +5 V
R
10 kΩ
(a) (b)
R1
R2 R3
5 kΩ 30 kΩ +12 V
Figure 3-23
3-20 Something causes R to short in Fig. 3-23a. What will the diode voltage be? What will happen to the diode?
Calculate the forward and the reverse resistance for each of these diodes.
3-28 In Fig. 3-23a, what value should R be to get a diode current of approximately 20 mA?
3-29 What value should R2 be in Fig. 3-23b to set up a diode current of 0.25 mA?
3-30 A silicon diode has a forward current of 500 mA at 1 V. Use the third approximation to calculate its bulk resistance.
Critical Thinking
3-27 Here are some diodes and their worst-case specifi cations:
Diode IF IR
1N914 10 mA at 1 V 25 nA at 20 V 1N4001 1 A at 1.1 V 10 A at 50 V 1N1185 10 A at 0.95 V 4.6 mA at 100 V
3-31 Given a silicon diode with a reverse current of 5 a at 25°C and 100 A at 100°C, calculate the surface leakage current.
3-32 The power is turned off and the upper end of R1 is grounded in Fig. 3-23b. Now you use an ohmme- ter to read the forward and reverse resistance of the diode. Both readings are identical. What does the ohmmeter read?
3-33 Some systems, like burglar alarms and comput- ers, use battery backup just in case the main source of power should fail. Describe how the circuit in Fig. 3-24 works.
15–V
SOURCE LOAD
– +
12 V
Figure 3-24
Multisim Troubleshooting Problems
The Multisim troubleshooting fi les are found on the In- structor Resources section of Connect for Electronic Principles, in a folder named Multisim Troubleshooting Circuits (MTC). See page XVI for more details. For this chapter, the fi les are labeled MTC03-34 through MTC03- 38 and are based on the circuit of Fig. 3-23b.
Open up and troubleshoot each of the respec- tive fi les. Take measurements to determine if there is a fault and, if so, determine the circuit fault.
3-34. Open up and troubleshoot fi le MTC03-34.
84 Chapter 3 3-35. Open up and troubleshoot fi le MTC03-35.
3-36. Open up and troubleshoot fi le MTC03-36.
3-37. Open up and troubleshoot fi le MTC03-37.
3-38. Open up and troubleshoot fi le MTC03-38.