Deck 10: Power Amplifiers

Question 1

With a class A amplifier,collector current flows throughout the cycle.

Answer 1

True

Question 2

When a transistor operates as class B,it clips off half a cycle.

Answer 2

True

Question 3

An amplifier can be described by their class of operation,by their interstage coupling,or by their frequency range.

Answer 3

True

Question 4

A power amplifier produces output power ranging from a few hundred milliwatts up to hundreds of watts.

Question 5

With amplifier class C operation,the collector current flows for

A) the entire cycle.
B) half the cycle.
C) less than half the cycle.
D) 56 milliseconds.

Question 6

A class AB amplifier is defined as an amplifier with a conduction angle between 180° and 360°.

Question 7

The input signal in a class C circuit is amplified to get a large output power with an efficiency approaching

A) 15 percent.
B) 50 percent.
C) 75 percent.
D) 100 percent.

Question 8

Harmonics are

A) multiples of a frequency.
B) instruments that provide sounds with metal reeds.
C) circuits used in audio amplifiers.
D) equations used in amplifier design.

Question 9

The efficiency of an amplifier is equal to dc output power divided by the ac input power.

Question 10

Class A operation of an amplifier means that the collector flows for only half the cycle.

Question 11

The amplifier stage that precedes the output stage is the driver.

Question 12

Class B and AB amplifiers require a stable operating point near cut-off.

Question 13

The three types of amplifier coupling methods are capacitive,transformer,and inductive.

Question 14

There are only two amplifier classes,A and
B.
FALSE

Question 15

Capacitive coupling and transformer coupling block dc voltage.

Question 16

A radio frequency amplifier is one that amplifies frequencies above 20 kHz.

Question 17

Cutoff and saturation clipping are undesirable because they distort the signal.

Question 18

If an amplifier circuit has a high quality factor (Q),the bandwidth is

A) large.
B) small.
C) equal to the upper half-power frequency.
D) dependant on the power supply.

Question 19

When a tank circuit is resonant,the ac load impedance seen by the collector current source is

A) maximum and purely resistive.
B) maximum and inductive.
C) minimum and purely resistive.
D) maximum and capacitive.

Question 20

Almost all class C amplifiers are linear audio amplifiers.

Question 21

In order to use a derating curve of a large power transistor

A) you must know the case temperature for the worst case.
B) you must use an npn transistor.
C) you must have a schematic diagram of the transistor.
D) you must reduce the ambient temperature.

Question 22

An amplifier that operates in the range of 20 Hz to 20 kHz is

A) a wideband amplifier.
B) a narrowband amplifier.
C) an audio amplifier.
D) a tuned amplifier.

Question 23

The type of amplifier coupling that can couple 0 Hz is ________.

A) direct
B) capacitive
C) transformer
D) transistor

Question 24

What type of amplifier produces output power ranging from a few hundred milliwatts up to hundreds of watts?

A) preamp
B) power amplifier
C) dc amplifier
D) RF tuned amplifier

Question 25

Class C operation means

A) the collector current flows for 360°of the ac cycle.
B) the collector current flows for half of the cycle.
C) the collector current flows for less than half of the cycle.
D) the collector current does not flow at all.

Question 26

An amplifier that is designed to work over a small range of frequencies is classified as ________.

A) small range
B) audio
C) RF
D) narrowband

Question 27

Types of amplifier coupling do not include ________.

A) transistor
B) direct
C) capacitive
D) transformer

Question 28

An amplifier's power gain equals

A) ac input power divided by the ac output power.
B) ac output power divided by the ac input power.
C) ac output power divided by the power supply voltage.
D) ac output power divided by the ac input current.

Question 29

The typical class C amplifier has

A) low efficiency.
B) a large duty cycle.
C) a small duty cycle.
D) no duty cycle.

Question 30

An amplifier whose ac load is a high-Q resonant tank is

A) an audio amplifier.
B) a wideband amplifier.
C) a dc amplifier.
D) a tuned RF amplifier.

Question 31

Amplifiers can be described by

A) their interstage coupling.
B) types of transistors used.
C) power supplies used.
D) power output.

Question 32

What factor places a limit on the allowable power dissipation of a transistor?

A) power supply
B) transistor case style
C) emitter-base junction
D) temperature at the collector junction

Question 33

In a well-designed large-signal amplifier,we get a maximum peak-to-peak unclipped output which is referred to as

A) ac output compliance.
B) dc output compliance.
C) peak compliance.
D) complementary compliance.

Question 34

An amplifier whose input is typically a radio tuner or CD player and produces a larger output suitable for driving tone and volume controls is a

A)power amp.
B) dc amplifier.
C) preamp.
D) tuned amp.

Question 35

With a class A amplifier,collector current flows

A) throughout the ac cycle.
B) for half the ac cycle.
C) for less than half of the ac cycle.
D) for 180° of the ac cycle.

Question 36

If the operating point of an amplifier is at or near saturation

A) the output signal will be distorted.
B) the collector current will be zero.
C) the output signal will be an exact reproduction of the input signal.
D) the input signal will be distorted.

Question 37

The power rating of a transistor can be effectively increased

A) by using bigger transistors.
B) by reducing power supply voltages.
C) by using heat sinks.
D) by using slow-blow fuses.

Question 38

If a transistor's ambient temperature is above 25°C

A) the power rating must be derated.
B) the power rating must be increased.
C) the power rating is invalid.
D) the power rating must be maximum.

Question 39

A direct-coupled amplifier is sometimes referred to as

A) a direct amplifier.
B) a dc amplifier.
C) an ac amplifier.
D) an alternating amplifier.

Question 40

The type of amplifier coupling that uses inductive action is ________.

A) direct
B) capacitive
C) transformer
D) transistor

Question 41

When the ac load impedance of a tank circuit is maximum and purely resistive

A) the circuit is off resonance.
B) the circuit is resonant.
C) the circuit is inductive.
D) the circuit is capacitive.

Question 42

When the emitter follower is used as a class A power amplifier at the end of a system,the operating point is typically located at the center of the ac load line

A) to get maximum peak-to-peak output.
B) to reduce the peak-to-peak output.
C) to keep the amplifier close to saturation.
D) to assure that clipping takes place.

Question 43

In an amplifier the dc current is referred to as the

A) constant current source.
B) current pump.
C) current drive.
D) current drain.

Question 44

An amplifier circuit that uses two transistors with one conducting for half a cycle while the other is off,and vice versa is called

A) a complementary amplifier.
B) a dual transistor amplifier.
C) push-pull amplifier.
D) push-push amplifier.

Question 45

When a transistor circuit operates as a class B amplifier

A) the output is an exact reproduction of the input.
B) one half cycle is clipped off.
C) there is no distortion.
D) most of the cycle is clipped off.

Question 46

The efficiency of a power amplifier is equal to the

A) ac output power divided by the dc input power.
B) ac output power divided by the ac input power.
C) dc output power divided by the dc input power.
D) dc output power divided by the ac input power.

Question 47

An advantage of a class B amplifier is

A) simplicity of design.
B) higher stage efficiency.
C) that current flows for the entire ac cycle.
D) that RF tuned circuits are used.

Question 48

The amplifier stage that precedes the output stage is referred to as the

A) preamp.
B) power amplifier.
C) tuned tank.
D) driver.