The following may have more than one right answer, Select the best answer. This is the one that is always true, or covers more
situations, etc.
1. What is true about the breakdown voltage in a zener diode? a. It decreases when current increases.
b. It destroys the diode.
c. It equals the current times the resistance. d. It is approximately constant.
2. Which of these is the best description of a zener diode? a. It is a diode.
b. It is a constant-voltage device. c. It is a constant-current device. d. It works in the forward region. 3. A zener diode
a. Is a battery
b. Acts like a battery in the breakdown region c. Has a barrier potential of 1 V
d. Is forward-biased
4. The voltage across the zener resistance is usually a. Small
b. Large
c. Measured in volts
d. Subtracted from the breakdown voltage
5. If the series resistance decreases in an unloaded zener regulator, the zener current
a. Decreases b. Stays the same c. Increases
6. In the second approximation, the total voltage across the zener diode is the sum of the breakdown voltage and the voltage across the
a. Source
b. Series resistor c. Zener resistance d, Zenerdiode
7. The load voltage is approximately constant when a zener diode is
a. Forward-biased b. Reverse-biased
c. Operating in the breakdown region d. Unbiased
8. In a loaded zener regulator, which is the largest current? a. Series current
b. Zener current c. Load current d. None of these
9. If the load resistance decreases in a zener regulator, the zener current
a. Decreases b. Stays the same c. Increases
d. Equals the source voltage divided by the series resistance
10. If the load resistance decreases in a zener regulator, the series current
a. Decreases b. Stays the same c. Increases
d. Equals the source voltage divided by the series resistance
11. When the source voltage increases in a zener regulator, which of these currents remains approximately constant?
a. Series current b. Zener current c. Load current d. Total current
12. If the zener diode in a zener regulator is connected with the wrong polarity, the load voltage will be closest to
a. 0.7 V b. 10 V c. 14 V d. 18 V
13. At high frequencies, ordinary diodes don't work properly because of
a. Forward bias b. Reverse bias c. Breakdown d. Charge storage
14. The capacitance of a varactor diode increases when the reverse voltage across it
a. Decreases b. Increases c. Breaks down d. Stores charges
15. Breakdown does not destroy a zener diode, provided the zener current is less than the
a. Breakdown voltage b. Zener test current
c. Maximum zener current racing d. Barrier potential
16. To display the digit 8 in a seven-segment indicator, a. C must be lighted
b. G must be off c. F must be on
d. All segments must be lighted 17. A photo diode is normally
a. Forward-biased b. Reverse-biased
c. Neither forward- nor reverse-biased d. Emitting light
18. When the light increases, the reverse minority-carrier current in a photodiode
a. Decreases b. Increases c. Is unaffected d. Reverses direction
19. The device associated with voltage-controlled capacitance is a
a. LED
b. Photodiode c. Varactor diode d. Zenerdiode
20. If the depletion layer gets wider, the capacitance a. Decreases
b. Stays the same c. Increases d. Is variable
21. When the reverse voltage increases, the capacitance a. Decreases
b. Stays the same c. Increases
d. Has more band width 22. The varactor is usually
a. Forward-biased b. Reverse-biased c. Unbiased
d. In the breakdown region
Basic Problems
Sec. 5-1 The Zener Diode
5-1. An unloaded zener regulator has a source voltage of 20V, a series resistance of 330 , and a zener voltage of 12 V. What is the zener current?
5-2. If the source voltage in Prob. 5-1 varies from 20 to 40 V, what is the maximum zener current?
5-3. If the series resistor of Prob. 5-1 has a tolerance of 10 percent, what is the maximum zener current?
Sec. 5-2 The Loaded Zener Regulator
5-4. If the zener diode is disconnected in Fig. 5-23, what is the load voltage?
5-5. Assume the supply voltage of Fig. 5-23 decreases from 20 to O V. At some point along the way, the zener diode will stop regulating: Find the supply voltage where regulation is lost. 5-6. Calculate all three currents in Fig. 5-23.
5-7. Assuming a tolerance of 10 percent in both resistors of Fig. 5-23, what is the maximum zener current?
5-8. Suppose the supply voltage of Fig. 5-23 can vary from 20 to 40 V. What is the maximum zener current?
5-9. What is the power dissipation in the resistors and zener diode of Fig. 5-23?
5-10. The zener diode of Fig. 5-23 is replaced with a IN961. What are the load voltage and the zener current?
5-11. The zener diode of Fig. 5-23 has a zener resistance of 11.5 . If the power supply has a ripple of I V, what is the ripple across the load resistor?
5-12. Draw the schematic diagram of a zener regulator with a supply voltage of 25 V, a series resistance of 470 , a zener voltage of I5 V, and a load resistance of 1 k . What are the load voltage and the zener current?
Sec. 5-3 Optoelectronic Devices
5-13. What is the current through the LED of Fig. 5-24?
5-14. If the supply voltage of Fig. 5-24 increases to 40 V, what is the LED current?
5-15. If the resistor is decreased to 1 k , what is the LED current in Fig. 5-24?