Online Questions and Answers Topic Outline
- MCQs in Introduction to Power Supplies | MCQs in General Filter Considerations | MCQs in Capacitor Filter | MCQs in RC Filter | MCQs in Discrete Transistor Voltage Regulation | MCQs in IC Voltage Regulators
Practice Exam Test Questions
Choose the letter of the best answer in each questions.
1. In which of the following applications is a pulsating dc voltage suitable?
- A. Battery charger
- B. Radio
- C. Stereo system
- D. Computer
2. Calculate the ripple of a filter output having a 20-V dc component and a 1.7 Vr(rms) ac component.
- A. 6%
- B. 8.5%
- C. 85%
- D. 58%
3. Calculate the voltage regulation of a power supply having VNL = 50 V and VFL = 48 V.
- A. 4.17%
- B. 5.2%
- C. 6.2%
- D. 7.1%
4. Across which of the following components of a power supply does the average (dc) voltage exist?
- A. Diodes
- B. Secondary of the transformer
- C. Capacitor filter
- D. None of the above
5. Calculate the ripple voltage of a full-wave rectifier with a 75-µF filter capacitor connected to a load drawing 40 mA.
- A. 1.20 V
- B. 1.28 V
- C. 1.32 V
- D. 1.41 V
6. What is the ratio of the period of the output voltage to the period of the input voltage in a full-wave rectifier?
- A. 0
- B. 0.5
- C. 1
- D. 2
7. A _____ -wave rectified signal has less ripple than a _____ -wave rectified signal and is thus better to apply to a filter.
- A. full, half
- B. half, full
8. If the value of full-load voltage is the same as the no-load voltage, the voltage regulation calculated is _____ %, which is the best expected.
- A. 0
- B. 1
- C. 99
- D. 100
9. In which period is the capacitor filter charged in a full-wave rectifier?
- A. The time during the positive cycle
- B. The time during which the diodes are not conducting
- C. The time during which the diode(s) is (are) conducting
- D. The time during the negative cycle
10. In which period is the capacitor filter discharged through the load in a full-wave rectifier?
- A. The time during the positive cycle
- B. The time during which the diodes are not conducting
- C. The time during which the diode(s) is (are) conducting
- D. The time during the negative cycle
11. If a peak rectified voltage for the full-wave filter circuit is 40 V, calculate the filter dc voltage if C = 75 µF and load current is 40 mA.
- A. 27.9 V
- B. 32.12 V
- C. 37.78 V
- D. 40 V
12. Calculate the ripple of a capacitor filter for a peak rectified voltage of 40 V, a capacitor value C = 75 µF, and a load current of 40 mA.
- A. 3.2%
- B. 3.59%
- C. 4.03%
- D. 4.59%
13. What is the ratio of the peak ripple voltage level to its rms voltage level?
- A. √3
- B. √2
- C. √3/2
- D. √2/2
14. The larger the value of the capacitor, the smaller the peak current drawn through the rectifying diodes.
- A. True
- B. False
15. What is the purpose of an additional RC filter section in a power supply circuit?
- A. Increase the dc voltage component
- B. Increase the ac voltage component
- C. Decrease the ac voltage component
- D. None of the above
16. Calculate the dc voltage across a 2-kΩ load for an RC filter section (R = 50 Ω, C = 20 µF). The dc voltage across the initial filter capacitor is Vdc = 50 V.
- A. 40.78 V
- B. 42.78 V
- C. 45.78 V
- D. 48.78 V
17. The purpose of the added RC section is to pass most of the dc component while reducing as much of the ac component as possible.
- A. True
- B. False
18. This circuit is an example of the ac equivalent of an RC filter.
- A. True
- B. False
19. For a full-wave rectifier with ac ripple at 120 Hz, the impedance of a capacitor can be calculated using XC = _____.
- A. 0.707 ÷ C
- B. 1.414 ÷ C
- C. 1.3 ÷ C
- D. 0.785 ÷ C
20. In a simple series regulator circuit, which of the following components is the controlling element?
- A. Load resistor
- B. Zener diode
- C. Transistor Q1
- D. None of the above
21. In this improved series regulator circuit, which of the following components is the sampling circuit?
- A. Zener diode
- B. Load resistor
- C. Either of the two transistors Q1 or Q2
- D. Resistors R1 and R2
22. In this op-amp series regulator circuit, which of the following components is the comparator circuit?
- A. Op-amp
- B. Transistor Q1
- C. R1 and R2 resistors
- D. Zener diode
23. What regulated output voltage is provided for the following circuit elements: R1 = 15 kΩ, R2 = 35 kΩ, and VZ = 11.2 V?
- A. 16.50 V
- B. 17 V
- C. 17.35 V
- D. 18.25 V
24. Which component(s) set(s) the voltage across the load in a basic transistor shunt regulator?
- A. Zener diode
- B. Transistor base-emitter voltage
- C. Both the Zener diode and the transistor base-emitter voltage
- D. None of the above
25. In an improved shunt regulator, which of the following components sets the reference voltage?
- A. Transistor Q1
- B. Zener diode
- C. Transistor Q2
- D. RS
26. For what range of load current can voltage regulators be selected for operation?
- A. Hundreds of picoamperes to tens of nanoamperes
- B. Hundreds of picoamperes to tens of milliamperes
- C. Hundreds of milliamperes to tens of amperes
- D. None of the above
27. For what range of fixed regulated voltages do the series 78xx regulators provide regulation?
- A. –5 V to +24 V
- B. +5 V to +24 V
- C. –5 V to –24 V
- D. None of the above
28. What is the typical dropout voltage for the 7812 fixed positive voltage regulator?
- A. 4 mV
- B. 100 mV
- C. 1.5 V
- D. 2 V
29. How many diodes conduct in the full-wave bridge rectifier while the capacitor is being charged?
- A. 1
- B. 2
- C. 3
- D. 4
30. What is the range of the voltage level of the LM317 adjusted voltage regulator?
- A. 0 V to 5 V
- B. 1.2 V to 37 V
- C. –5 V to –24 V
- D. 5 V to 24 V
31. What are the typical values of Vref and Iadj for the LM317 adjustable voltage regulator?
- A. 1.0 V, 100 mA
- B. 1.5 V, 100 mA
- C. 1.25 V, 100 μA
- D. 1.25 V, 10 mA
32. The 7812 regulator IC provides _____.
- A. 5 V
- B. –5 V
- C. 12 V
- D. –12 V
33. The 7912 regulator IC provides _____ .
- A. 5 V
- B. –5 V
- C. 12 V
- D. –12 V
34. The 7905 regulator IC provides _____.
- A. 5 V
- B. –5 V
- C. 12 V
- D. –12 V
35. The 7805 regulator IC provides _____.
- A. 5 V
- B. –5 V
- C. 12 V
- D. –12 V
FILL-IN-THE-BLANKS
1. A complete power supply has a _____.
- A. rectifier
- B. filter
- C. voltage regulator
- D. All of the above
2. The output resulting from a rectifier is a(n) _____.
- A. ac voltage
- B. pure dc voltage
- C. pulsating dc voltage
- D. None of the above
3. The _____ the ac variation with respect to the dc level, the _____ the filter circuit's operation.
- A. smaller, better
- B. larger, better
- C. smaller, worse
- D. None of the above
4. A dc voltmeter reads the _____ while measuring a pulsating dc voltage.
- A. ac component of the signal
- B. average of the signal
- C. peak of the pulsating signal
- D. None of the above
5. The filter output voltage of a power supply _____ when load current is drawn from the supply.
- A. remains the same
- B. is increased
- C. is reduced
- D. None of the above
6. The _____ the voltage regulation, the _____ the operation of the voltage supply circuit.
- A. smaller, better
- B. larger, better
- C. smaller, worse
- D. None of the above
7. A full-wave rectified signal has _____ dc component and _____ ripple than (as) the half-wave rectified voltage.
- A. a larger, more
- B. a smaller, less
- C. the same, less
- D. a larger, less
8. If the value of the full-load voltage is the same as the no-load voltage, the voltage regulation calculated is _____.
- A. 0%
- B. a negative percentage
- C. a positive percentage
- D. None of the above
9. In a half-wave rectifier, the dc voltage level is _____ the ripple voltage level.
- A. smaller than
- B. the same as
- C. larger than
- D. None of the above
10. In a full-wave rectifier, the dc voltage level is _____ the ripple voltage level.
- A. smaller than
- B. the same as
- C. larger than
- D. None of the above
11. In a full-wave rectifier, if no load were connected across the capacitor, the output voltage would ideally be a(n) _____.
- A. ac voltage
- B. constant dc voltage
- C. pulsating dc voltage
- D. ramp voltage
12. The output of a loaded power supply is _____ that of the unloaded.
- A. the same as
- B. larger than
- C. smaller than
- D. None of the above
13. The charging and discharging of the capacitor filter take _____ of the period of the input voltage.
- A. 0.25
- B. 0.5
- C. 0.75
- D. 1
14. The frequency of the output voltage of a full-wave rectifier is _____ the frequency of its input voltage.
- A. the same as
- B. twice
- C. one-half
- D. one-third
15. The ripple voltage Vr is a result of the _____.
- A. conduction of the diode(s)
- B. transformer windings
- C. charging and discharging of the capacitor
- D. load resistor
16. The _____ values of capacitor filter provide _____ ripple and _____ average voltage.
- A. larger, more, higher
- B. smaller, less, lower
- C. smaller, more, higher
- D. larger, less, higher
17. The _____ the diode conduction time, the _____ the amount of the charging current through the capacitor filter.
- A. shorter, larger
- B. shorter, smaller
- C. longer, larger
- D. None of the above
18. In a current-limiting circuit, _____ provide(s) the limiting of the maximum load current.
- A. the Zener diode
- B. the short-circuit resistor Rsc
- C. the transistor Q1
- D. both the short-circuit resistor Rsc and transistor Q2
19. In a foldback configuration, limiting the current reduces _____, protecting the load from overcurrent as well as protecting the regulator.
- A. the output voltage
- B. the output current
- C. both the output voltage and output current
- D. None of the above
20. A type of regulator circuit that is quite popular for its efficient transfer of power to the load is the _____.
- A. current-limiting voltage regulator
- B. switching regulator
- C. foldback limiting regulator
- D. op-amp series regulator
21. Regulator IC units contain the circuitry for the _____.
- A. reference source
- B. comparator amplifier
- C. control device and overload protection
- D. All of the above
22. IC units provide regulation of _____.
- A. a fixed positive voltage
- B. a fixed negative voltage
- C. an adjustably set voltage
- D. All of the above
23. The specification sheet for the 7812 fixed positive voltage regulator shows that the output voltage could be as low as _____ or as high as _____.
- A. 11.5 V, 12.5 V
- B. 11.2 V, 12.2 V
- C. 11 V, 13 V
- D. 8 V, 15 V
24. The series 7900 ICs are _____.
- A. positive voltage regulators
- B. negative voltage regulators
- C. both positive and negative voltage regulators
- D. adjustable-set voltage regulators
25. The _____ is (are) an adjustable voltage regulator.
- A. series 7800 ICs
- B. series 7900 ICs
- C. LM317
- D. None of the above
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