Deck 7: Power Amplifiers

Question 1

The ac load line is the same as the dc load line when the ac collector resistance equals the

A)supply voltage divided by collector current.
B)ac emitter resistance.
C)dc collector resistance.
D)dc emitter resistance.

Answer 1

C

Question 2

For a class A CE amplifier, the power dissipation, PDQ

A)increases when the peak- to- peak load voltage increases.
B)is zero with no input signal.
C)is maximum when the transistor is driven to cutoff.
D)is maximum when there is no input signal.

Answer 2

D

Question 3

An application for a power amplifier to operate at radio frequencies is needed. The most likely choice would be a amplifier.

A)class A
B)class B
C)class C
D)class AB

Answer 3

C

Question 4

The amplifier with the most distortion would be a _ amplifier.

A)class A
B)class B
C)class C
D)class AB

Question 5

Refer to the figure above. The dc voltage across RL was measured at 10 V. A possible problem, if any, might be that

A)C1 is open.
B)R1 is open.
C)C3 is open.
D)C3 is shorted.

Question 6

The input signal of a class C amplifier

A)is amplified and inverted.
B)produces brief pulses of collector current.
C)is negatively clamped at the base.
D)All of the above.

Question 7

For maximum peak- to- peak output voltage, the Q- point should be

A)at the center of the ac load line.
B)near saturation.
C)at the center of the dc load line.
D)near cutoff.

Question 8

Refer to the figure above. If R1 opened, and Vin at the base was large, Vout at the collector would

A)increase.
B)distort.
C)decrease.
D)remain the same.

Question 9

For a class C amplifier, there is collector current for

A)less than 180° of the input cycle.
B)0° of the input cycle.
C)210° of the input cycle.
D)360° of the input cycle.

Question 10

Refer to the figure above. If RL shows a zero signal voltage on an oscilloscope, the problem might be that

A)C3 is open.
B)R1 is open.
C)BE1 is open.
D)BE2 is open.

Question 11

If a class A amplifier has a voltage gain of 50 and a current gain of 75, the power gain is

A)3750.
B)75.
C)50.
D)1500.

Question 12

A CE amplifier has a load power of 10 mW and the dc power is 215 mW. The efficiency is

A)46.5%.
B)0%.
C)4.65%.
D)25%.

Question 13

A class AB amplifier is biased

A)slightly above the center of the load line.
B)at cutoff.
C)slightly above cutoff.
D)at the center of the load line.

Question 14

For a Q- point near the center of the dc load line, clipping is more likely to occur on the

A)positive peak of input voltage.
B)negative peak of emitter voltage.
C)negative peak of output voltage.
D)positive peak of output voltage.

Question 15

In a class AB push- pull amplifier, the transistors are biased slightly above cutoff to avoid

A)unusually high efficiency.
B)a low input impedance.
C)crossover distortion.
D)negative feedback.

Question 16

If an application for an amplifier requires operation in a linear mode, the most likely choice would be a

A)class A.
B)class B.
C)class C.
D)class AB.

Question 17

For a class AB push- pull amplifier, diode bias is used to

A)saturate the output transistors.
B)ensure thermal runaway.
C)allow the transistors to conduct for 360°.
D)avoid thermal runaway.

Question 18

Power MOSFETs have several advantages over bipolar power transistors. Which of the following statements is not correct?

A)Less prone to ESD damage when compared to BJTs
B)Have simpler biasing circuits
C)Have a low voltage drop across the device under high voltage and current conditions
D)Can be connected in parallel to increase current capacity

Question 19

Heat sinks reduce the

A)ambient temperature.
B)collector current.
C)transistor power.
D)junction temperature.

Question 20

Refer to the figure above. The purpose for the diodes D1 and D2 is

A)to allow the correct bias voltages on the two bases.
B)to apply equal signals to each transistor.
C)to maintain constant bias with temperature changes.
D)All of the above.

Question 21

The collector current of a class C amplifier

A)flows for half a cycle.
B)is negatively clamped.
C)is an amplified version of the input voltage.
D)has harmonics.

Question 22

For each transistor in a class B amplifier, there is collector current for

A)90° of the input cycle.
B)360° of the input cycle.
C)180° of the input cycle.
D)270° of the input cycle.

Question 23

If a class A amplifier has RC = 4.7 k▲ and RE = 1.5 k▲ and VCC = 24 V, ICsat)is

A)3.87 mA.
B)16 mA.
C)5.1 mA.
D)0 mA.

Question 24

A class B amplifier conducts for of the cycle.

A)90°
B)180°
C)45°
D)360°

Question 25

When the Q- point is at the center of the ac load line, a maximum signal can be obtained.

A)class A
B)class B
C)class C
D)None of the above.

Question 26

To improve the efficiency of an amplifier, you have to

A)reduce load power.
B)reduce the supply voltage.
C)decrease unwanted power losses.
D)increase the dc current.

Question 27

Refer to the figure above. During the positive input alternation, Q1 is and Q2 is _ .

A)on, off
B)off, off
C)off, on
D)on, on

Question 28

The quiescent collector current is the same as

A)ac load resistor current.
B)dc collector current.
C)ac collector current.
D)None of the above.

Question 29

Class C amplifiers are almost always

A)tuned RF amplifiers.
B)wideband.
C)operated at audio frequencies.
D)transformer- coupled between stages.

Question 30

The maximum efficiency for a class A amplifier is about

A)100%.
B)25%.
C)75%.
D)50%.

Question 31

Refer to the figure above. The purpose of the diode is to bias the amplifier as

A)class A.
B)class B.
C)class C.
D)class AB.

Question 32

The class of amplifiers that is the most efficient and has the most distortion is class amplifiers.

A)A
B)B
C)C
D)AB

Question 33

The ac load line usually

A)has less slope than the dc load line.
B)is steeper than the dc load line.
C)is horizontal.
D)equals the dc load line.

Question 34

The maximum efficiency of a class B push- pull amplifier is

A)100 percent.
B)50 percent.
C)25 percent.
D)79 percent.

Question 35

Under no- signal or quiescent conditions, the transistors of a class B push- pull amplifier

A)get quite hot.
B)are in saturation.
C)dissipate very little power.
D)have excessively high power dissipation.

Question 36

An amplifier has two load lines because

A)it has two equivalent circuits.
B)the dc and ac circuits are different.
C)it has ac and dc collector resistances.
D)All of the above.

Question 37

Push- pull amplifiers often use class amplifiers.

A)A
B)B or AB
C)C

Question 38

Refer to the figure above. If the diode opened, this amplifier would be operating as

A)class A.
B)class B.
C)class C.
D)class AB.