 # MCQs in Boylestad: Power Amplifiers

(Last Updated On: December 8, 2017)

This is the Multiple Choice Questions in Power Amplifiers from the book Electronic Devices and Circuit Theory 10th Edition by Robert L. Boylestad. If you are looking for a reviewer in Electronics Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

### Online Questions and Answers Topic Outline

• MCQs in Introduction—Definitions and Amplifier Types
• MCQs in Series-Fed Class A Amplifier
• MCQs in Transformer-Coupled Class A Amplifier
• MCQs in Class B Amplifier Operation
• MCQs in Class B Amplifier Circuits
• MCQs in Amplifier Distortion
• MCQs in Power Transistor Heat Sinking
• MCQs in Class C and Class D Amplifiers

### Practice Exam Test Questions

Choose the letter of the best answer in each questions.

1. Which of the following is (are) power amplifiers?

• a. Class A
• b. Class B or AB
• c. Class C or D
• d. All of the above

2. By how much does the output signal vary for a class AB power amplifier?

• a. 360º
• b. 180º
• c. Between 180º and 360º
• d. Less than 180º

3. Which type of power amplifier is biased for operation at less than 180º of the cycle?

• a. Class A
• b. Class B or AB
• c. Class C
• d. Class D

4. Which type of amplifier uses pulse (digital) signals in its operation?

• a. Class A
• b. Class B or AB
• c. Class C
• d. Class D

5. Which of the power amplifiers has the lowest overall efficiency?

• a. Class A
• b. Class B or AB
• c. Class C
• d. Class D

6. Which of the following describe(s) a power amplifier?

• a. It can handle large power.
• b. It can handle large current.
• c. It does not provide much voltage gain.
• d. All of the above

7. _____ amplifiers primarily provide sufficient power to an output load to drive a speaker from a few watts to tens of watts.

• a. Small-signal
• b. Power
• c. None of the above

8. The main features of a large-signal amplifier is the circuit’s ______.

• a. power efficiency
• b. maximum power limitations
• c. impedance matching to the output device
• d. All of the above

9. This is an example of the output swing for a class _____ amplifier. • a. A
• b. B
• c. AB
• d. C
• e. D

10. This is an example of the output swing for a class _____ amplifier. • a. A
• b. B
• c. AB
• d. C
• e. D

11. Class AB operation is _____ operation.

• a. similar to class A
• b. similar to class B
• c. similar to class C
• d. None of the above

12. Which operation class is generally used in radio or communications?

• a. A
• b. B
• c. AB
• d. C
• e. D

13. Categorize the power efficiency of each class of amplifier, from worst to best.

• a. A, B, AB, D
• b. A, AB, D, B
• c. A, AB, B, D

14. What is the maximum efficiency of a class A circuit with a direct or series-fed load connection?

• a. 90%
• b. 78.5%
• c. 50%
• d. 25%

15. What is the ratio of the secondary voltage to the primary voltage with the turn ratio in the winding

• a. N2/N1
• b. (N1/N2)2
• c. (N1/N2)1/3
• d. N1 × N2

16. Calculate the effective resistance seen looking into the primary of a 20:1 transformer connected to an 8- Ω load.

• a. 3.2 kΩ
• b. 3.0 kΩ
• c. 2.8 kΩ
• d. 1.8 kΩ

17. What transformer turns ratio is required to match an 8-speaker load so that the effective load resistance seen at the primary is 12.8 k?

• a. 20:1
• b. 40:1
• c. 50:1
• d. 60:1

18. Calculate the efficiency of a transformer-coupled class A amplifier for a supply of 15 V and an output of V(p) = 10 V.

• a. 25%
• b. 33.3%
• c. 50%
• d. 78.5%

19. The maximum efficiency of a transformer-coupled class A amplifier is _____.

• a. 25%
• b. 50%
• c. 78.5%
• d. 63.6%

20. What is the maximum efficiency of a class B circuit?

• a. 90%
• b. 78.5%
• c. 50%
• d. 25%

21. How many transistors must be used in a class B power amplifier to obtain the output for the full cycle of the signal?

• a. 0
• b. 1
• c. 2
• d. 3

22. In class B operation, at what fraction of VCC should the level of VL(p) be to achieve the maximum power dissipated by the output transistor?

• a. 0.5
• b. 0.636
• c. 0.707
• d. 1

23. Class B operation is provided when the dc bias leaves the transistor biased just off, the transistor turning on when the ac signal is applied.

• a. True
• b. False

24. Calculate the efficiency of a class B amplifier for a supply voltage of VCC = 20 V with peak output voltage of VL(p) = 18 V. Assume RL = 16 Ω.

• a. 78.54%
• b. 75%
• c. 70.69%
• d. 50%

25. Which of the following is (are) the disadvantage(s) of a class B complementary-symmetry circuit?

• a. It needs two separate voltage sources.
• b. There is crossover distortion in the output signal.
• c. It does not provide exact switching of one transistor off and the other on at the zero-voltage condition.
• d. All of the above

26. Which of the push-pull amplifiers is presently the most popular form of the class B power amplifier?

• a. Quasi-complementary
• b. Transformer-coupled
• c. Complementary-symmetry
• d. None of the above

27. nMOS and pMOS transistors can be used for class B.

• a. True
• b. False

28. Calculate the harmonic distortion component for an output signal having fundamental amplitude of 3 V and a second harmonic amplitude of 0.25 V.

• a. 3.83%
• b. 38.3%
• c. 83.3%
• d. 8.33%

29. Which of the following instruments displays the harmonics of a distorted signal?

• a. Digital multimeter
• b. Spectrum analyzer
• c. Oscilloscope
• d. Wave analyzer

30. Which of the following instruments allows more precise measurement of the harmonic components of a distorted signal?

• a. Digital multimeter
• b. Spectrum analyzer
• c. Oscilloscope
• d. Wave analyzer

31. What is the maximum temperature rating for silicon power transistors?

• a. 50º to 80º
• b. 100º to 110º
• c. 150º to 200º
• d. 250º to 300º

32. Which of the power amplifiers is not intended primarily for large-signal or power amplification?

• a. Class A
• b. Class B or AB
• c. Class C
• d. Class D

33. Determine what maximum dissipation will be allowed for a 70-W silicon transistor (rated at 25ºC) if derating is required above 25ºC by a derating factor of 0.6 W/ºC at a case temperature of 100º.

• a. 25 W
• b. 30 W
• c. 35 W
• d. 40 W

34. A silicon power transistor is operated with a heat sink (θSA = 1.5ºC/W). The transistor, rated at 150 W (25ºC), has θJC = 0.5º C/W, and the mounting insulation has θCS = 0.6 ºC/W. What is the maximum power that can be dissipated if the ambient temperature is 50ºC and TJmax = 200 ºC?

• a. 61.5 W
• b. 60.0 W
• c. 57.7 W
• d. 55.5 W

35. Which of the following transistors has been quite popular as the driver device for class D amplification?

• a. BJT
• b. FET
• c.UJT
• d. MOSFET

### FILL-IN-THE-BLANKS

1. Power amplifiers primarily provide sufficient power to an output load, typically from _____ to _____.

• A. a few kW, tens of kW
• B. 500 W, 1 kW
• C. 100 W, 500 W
• D. a few W, tens of W

2. The main feature(s) of a large-signal amplifier is (are) the _____.

• A. circuit’s power efficiency
• B. maximum amount of power that the circuit is capable of handling
• C. impedance matching to the output
• D. All of the above

3. In _____ power amplifiers, the output signal varies for a full 360º of the cycle.

• A. class A
• B. class B or AB
• C. class C
• D. class D

4. In class B power amplifiers, the output signal varies for _____ of the cycle.

• A. 360º
• B. 180º
• C. between 180º and 360º
• D. less than 180º

5. _____ amplifiers have the highest overall efficiency.

• A. Class A
• B. Class B or AB
• C. Class C
• D. Class D

6. Class D operation can achieve power efficiency of over _____.

• A. 90%
• B. 78.5%
• C. 50%
• D. 25%

7. The beta of a power transistor is generally _____.

• A. more than 200
• B. 100 to 200
• C. less than 100
• D. 0

8. A form of class A amplifier having maximum efficiency of _____ uses a transformer to couple the output signal to the load.

• A. 90%
• B. 78.5%
• C. 50%
• D. 25%

9. The reflected impedance seen from one side of the transformer to the other side is _____.

• A. N1/N2
• B. (N1/N2)2
• C. (N1/N2)1/3
• D. N1× N2

10. In a class A transformer-coupled power amplifier, _____ winding resistance of the transformer determine(s) the dc load line for the circuit.

• A. the ac
• B. the dc
• C. both the ac and dc
• D. neither the ac nor dc

11. The slope of the ac load line in the class A transformer-coupled transistor is _____.

• A. –1/RL (load resistor)
• B. 1/(a2RL)
• C. –1/(a2RL)
• D. 1/RL

12. The amount of power dissipated by the transistor is the _____ of that drawn from the dc supply (set by the bias point) and the amount delivered to the ac load.

• A. product
• B. difference
• C. average

13. A class A amplifier dissipates _____ power when the load is drawing maximum power from the circuit.

• A. the least
• B. about the same
• C. the most
• D. None of the above

14. In a class A transformer-coupled amplifier, the _____ the value of VCEmax and the _____ the value of VCEmin, the _____ the efficiency to (from) the theoretical limit of 50%.

• A. larger, smaller, farther
• B. larger, smaller, closer
• C. smaller, larger, closer
• D. None of the above

15. In class B operation, the current drawn from a single power supply has the form of _____ rectified signal.

• A. a full-wave
• B. a half-wave
• C. both a full-wave and a half-wave
• D. None of the above

16. The highest efficiency is obtained in class B operation when the level of VL(p) is equal to _____.

• A. 0.25VCC
• B. 0.50VCC
• C. VCC
• D. 2VCC

17. _____ transistors can be used to build a class B amplifier.

• A. npn and pnp
• B. nMOS and pMOS
• C. Both npn and pnp or nMOS and pMOS
• D. None of the above

18. The complementary Darlington-connected transistor for a class B amplifier provides _____ output current and _____ output resistance.

• A. higher, higher
• B. higher, lower
• C. lower, lower
• D. lower, higher

19. The fundamental component is typically _____ any harmonic component.

• A. larger than
• B. the same as
• C. smaller than
• D. None of the above

20. In Fourier technique, any periodic distorted waveform can be represented by _____ the fundamental and all harmonic components.

• A. multiplying
• B. subtracting
• C. dividing

21. Improvement in production techniques of power transistors have _____.

• A. produced higher power ratings in small-sized packaging cases
• B. increased the maximum transistor breakdown voltage
• C. provided faster-switching power transistors
• D. All of the above

22. The greater the power handled by the power transistor, _____ the case temperature.

• A. the higher
• B. the lower
• C. there is no change in
• D. None of the above

23. The _____ has the hottest temperature in a power transistor.

• A. heat sink
• B. case
• C. junction
• D. None of the above

24. A heat sink provides _____ thermal resistance between case and air.

• A. a high
• B. a low
• C. the same
• D. None of the above

25. A _____ power amplifier is limited to use at one fixed frequency.

• A. class A
• B. class B or AB
• C. class C
• D. class D

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MCQs in Boylestad: Power Amplifiers
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