Deck 33: Power Amplifiers

Question 1

The main disadvantage of a class B or AB operation is that two ______________ must be used to get a linear reproduction of the input waveform being applied.

Answer 1

transistors

Question 2

With class ______________ operation, crossover distortion is entirely eliminated.

Answer 2

AB

Question 3

______________ distortion results in a class B push-pull amplifier when the transistors are biased at cutoff.

Answer 3

Crossover

Question 4

______________ bias is a form of biasing for class B push-pull amplifiers that uses diodes to provide a slight amount of forward bias for the base-emitter junctions of each transistor.

Question 5

The collector current for a transistor in a class C amplifier flows for ______________ degrees or less of the input waveform.

Question 6

Class C amplifiers can be used in tuned rf amplifiers where undesired ______________ frequencies can be filtered out.

Question 7

Tuned class C amplifiers can be used as frequency ______________ by tuning the LC tank circuit to a harmonic of the input frequency.

Question 8

The class of operation for an amplifier determines its power ______________.

Question 9

The characteristics of a class ______________ amplifier include both low distortion and low power efficiency.

Question 10

If the signal amplitude at the input of a class A amplifier is too large, either or both peaks of the output waveform will be ______________ or flattened.

Question 11

A true class B amplifier is biased such that the Q point is located at

A) the center of the load line
B) cutoff
C) saturation
D) the linear portion of the load line

Question 12

To provide a linear output, many class B push-pull audio amplifiers are biased to operate as what class amplifier?

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

Question 13

The distortion that occurs in a class B push-pull amplifier when the transistors are biased at cutoff is called

A) crossover distortion
B) overdriven amp distortion
C) harmonic distortion
D) clipping

Question 14

What is the form of bias used for class B push-pull amplifiers that uses diodes to provide a slight amount of forward bias for the base-emitter junctions of each transistor?

A) Voltage-divider bias
B) Self-bias
C) Diode bias
D) Current-source bias

Question 15

Which of the following is not an advantage of using a split supply class B push-pull?

A) More output power
B) No dc current flow in speaker load
C) Low frequency response greatly improved
D) Lower supply voltages can be used

Question 16

In which amplifier class does the collector current flow for 120° or less of the input waveform?

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

Question 17

Class C amplifiers are generally used in

A) preamplifiers
B) audio amplifiers
C) tuned rf amplifiers
D) stereo amplifiers

Question 18

Typical class C amplifiers have efficiencies of approximately

A) 5%
B) 20%
C) 50%
D) 90%

Question 19

The voltage gain of a class C rf amplifier is maximum

A) below the resonant frequency of the tank circuit
B) at the resonant frequency of the tank circuit
C) above the resonant frequency of the tank circuit
D) at audio frequencies only

Question 20

Those frequencies in which the voltage gain is 70.7% or more of its maximum at resonance is referred to as the

A) frequency response
B) frequency range
C) bandpass
D) bandwidth

Question 21

By tuning an LC tank circuit to a harmonic of the input frequency, the tuned class C amplifiers can be used as

A) frequency counters
B) frequency multipliers
C) frequency dividers
D) frequency generators

Question 22

A circuit capable of delivering large amounts of power to a low impedance load is considered a(n)

A) preamplifier
B) small-signal amplifier
C) power amplifier
D) operational amplifier

Question 23

Which of the following is not an amplifier class?

A) A
B) B
C) BC
D) C

Question 24

The percentage of the ac input cycle that produces an output current defines the

A) operating point for an amplifier
B) number of possible amplifier stages
C) class of operation for an amplifier
D) amount of biasing required for linear operation

Question 25

The collector current of a transistor in a class A amplifier flows for

A) approximately 60° of the input waveform
B) approximately 120° of the input waveform
C) 180° of the input waveform
D) 360° of the input waveform

Question 26

What is typically used to reproduce a full sine-wave at its output for each short pulse of collector current in a class C amplifier?

A) Oscillator circuit
B) Regulator circuit
C) Tank circuit
D) Bridge circuit

Question 27

Which class amplifier has characteristics that include very high efficiency and severe distortion of the input signal?

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

Question 28

The percentage of the dc input power that is converted to useful ac power output is the

A) class of amplifier
B) conduction percentage of an amplifier
C) power ratio of an amplifier
D) percent efficiency of an amplifier

Question 29

The higher frequencies in the output voltage of an amplifier are substantially affected by what capacitance?

A) Coupling capacitors
B) Bypass capacitors
C) Stray wiring capacitance
D) Varactor diodes

Question 30

The maximum possible efficiency of an RC coupled class A amplifier cannot exceed what percentage no matter what is done?

A) 8.33%
B) 18.33%
C) 28.33%
D) 38.33%

Question 31

By what capacitance are the higher frequencies in the output voltage of an amplifier substantially affected?

A) Coupling capacitors
B) Bypass capacitors
C) Stray wiring capacitance
D) Varactor diodes

Question 32

What percentage cannot exceed the maximum possible efficiency of an RC coupled class A amplifier, no matter what is done?

A) 8.33%
B) 18.33%
C) 28.33%
D) 38.33%

Question 33

A power amplifier is a circuit capable of delivering large amounts of power to a low impedance load.

Question 34

. The three general classes for power amplifiers are class A, class B, and class C.

Question 35

The class of operation for an amplifier is defined by the percentage of the ac input cycle that produces an output current.

Question 36

The collector current of a transistor in a class A amplifier flows for 180° of the input waveform.

Question 37

A class A amplifier cannot be used as a linear amplifier.

Question 38

The collector current of a transistor in a class B amplifier flows for the full 360° of the input signal.

Question 39

The characteristics of a class B amplifier using a single transistor include medium efficiency and severe distortion.

Question 40

The typical operation of a class C amplifier provides a collector current that flows for approximately 120° or less of the input cycle.

Question 41

The signal amplitude of any class A amplifier at the input should not be large enough to drive the amplifier into either cutoff or saturation.

Question 42

With no ac input signal applied to the amplifier, the transistor has a power dissipation equal to the voltage, collector to emitter at quiescence times the collector current at quiescence.

Question 43

In a class A amplifier, the power dissipation in the transistor decreases when an ac signal is applied to the input.

Question 44

The percent efficiency of any amplifier is defined as the percentage of the ac input power that is converted to useful dc power output.

Question 45

The ac voltage at the collector is capacitively coupled to the load resistor in an RC coupled amplifier.

Question 46

Coupling and bypass capacitors affect the output of an amplifier at low frequencies.

Question 47

The maximum possible efficiency of an RC coupled class A amplifier cannot exceed 8.33% no matter what is done.