Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
Impedance matching is important for ________.
1)
A)
maximum power transfer from source to load
B)
maximum voltage transfer from source to load
C)
maximum impedance transfer from source to load
D)
maximum current transfer from source
Answer:
A
A)
B)
C)
D)
2)
With transformer coupling the maximum theoretical efficiency of a class A amplifier can be
increased up to ________.
2)
A)
55%
B)
60%
C)
50%
D)
45%
Answer:
C
A)
B)
C)
D)
3)
Complementary–symmetry amplifiers are generally preferred over standard push–pull amplifiers
because ________.
3)
A)
they do not require the use of an output transformer
B)
they use complementary transistors
C)
they have high efficiency ratings
D)
they can drive lower impedance loads
Answer:
A
A)
B)
C)
D)
4)
The maximum theoretical efficiency of a class A amplifier is equal to ________.
4)
A)
15%
B)
30%
C)
25%
D)
20%
Answer:
C
A)
B)
C)
D)
1
5)
A class AB transistor amplifier using complementary transistors is biased by a power supply that is
±18Vdc. The value of VCE(OFF) for either transistor is approximately equal to ________.
5)
A)
10 V
B)
18 V
C)
36 V
D)
8 V
Answer:
B
A)
B)
C)
D)
6)
Class D amplifiers have a maximum theoretical efficiency of ________.
6)
A)
over 90%
B)
25%
C)
50%
D)
78.5%
Answer:
A
A)
B)
C)
D)
7)
The circuit that converts the output from a class D amplifier back to an analog signal is ________ .
7)
A)
a low–pass filter
B)
a comparator
C)
a high–pass filter
D)
a bandpass filter
Answer:
A
A)
B)
C)
D)
8)
Transformer action with a class A power amplifier allows the engineer to design for ________.
8)
A)
impedance transformation
B)
voltage transformation
C)
current transformation
D)
All of the above
Answer:
D
A)
B)
C)
D)
9)
Class B amplifiers ________.
9)
A)
usually contain a single BJT that conducts through 360° of the ac input cycle
B)
usually contain an LC tank circuit in the BJT collector circuit
C)
provide an output signal for 360° the input signal cycle
D)
usually contain a single BJT that conducts through 270° of the ac input signal
Answer:
C
A)
B)
C)
D)
2
10)
A transformer–coupled class A amplifier has a transformer turns ratio of 1 : 4.5 and a load
resistance of 30 . The peak–to–peak value of VCE is 12 V. What is the approximate power that is
delivered to the load?
10)
A)
47 W
B)
71 W
C)
119 W
D)
95 W
Answer:
D
A)
B)
C)
D)
11)
A class A amplifier has an 8 VPP output that is being applied to a 200 load. What is the total ac
load power?
11)
A)
640 mW
B)
80 mW
C)
40 mW
D)
320 mW
Answer:
C
A)
B)
C)
D)
12)
A given transistor has a power derating factor of 1.8 mW/° C and a power dissipation rating of 400
mW at 25° C. How much power can the device dissipate at 120° C?
12)
A)
229 mW
B)
355 mW
C)
216 mW
D)
184 mW
Answer:
A
A)
B)
C)
D)
13)
Calculate the total harmonic distortion for a signal that has the following amplitude components:
Fundamental = 2.5 V
Second harmonic = 0.25 V
Third harmonic = 0.1 V
Fourth harmonic = 0.025 V
13)
A)
THD% = 10.95%
B)
THD% = 10.82%
C)
THD% = 10.68%
D)
THD% = 10.74%
Answer:
B
A)
B)
C)
D)
14)
Class C amplifiers are used mostly in ________ circuits.
14)
A)
audio
B)
power
C)
digital
D)
communication
Answer:
D
A)
B)
C)
D)
3
15)
Crossover distortion in class B amplifiers is prevented by ________.
15)
A)
biasing the transistors deeply into cutoff
B)
using complementary–symmetry transistors
C)
increasing the load resistance
D)
biasing the transistors slightly above cutoff
Answer:
D
A)
B)
C)
D)
16)
A fixed–bias class A amplifier has values of VCC= 10 V, IBQ = 450 µA, and ICQ = 10.55 mA. What
is the total power that the circuit is drawing from the dc power supply?
16)
A)
110 mW
B)
4.5 mW
C)
1.21 mW
D)
Cannot be determined from the information given
Answer:
A
A)
B)
C)
D)
17)
A transformer coupled class A amplifier has a transformer turns ratio of 4.5 : 1 and a load resistance
of 30 . What is approximately the value of the effective AC load resistance seen by the collector of
the transistor?
17)
A)
400
B)
700
C)
500
D)
600
Answer:
D
A)
B)
C)
D)
18)
The dc load line of a transformer–coupled class A amplifier is ________.
18)
A)
a near–vertical line
B)
a near–horizontal line
C)
identical to that of an RC–coupled class A amplifier
D)
None of the above
Answer:
A
A)
B)
C)
D)
4
19)
Quasi–complementary push–pull amplifiers ________ .
19)
A)
use a Darlington pair as an output
B)
use an npn transistors for all high–current outputs
C)
use a feedback pair as an output
D)
all of the above
Answer:
D
A)
B)
C)
D)
20)
A class C amplifier ________.
20)
A)
conducts through 180° of the input waveform
B)
conducts through less than 180° of the input waveform
C)
conducts between 180° and 360° degrees of the input waveform, depending on the amount of
dc bias
D)
works only with digital and pulsed waveforms
Answer:
B
A)
B)
C)
D)
21)
BJT class C amplifiers usually contain ________.
21)
A)
an LC tank circuit in the collector circuit
B)
a single BJT that conducts through 270° of the ac input cycle
C)
two transistors
D)
a single BJT that conducts through 360° of the ac input cycle
Answer:
A
A)
B)
C)
D)
22)
A transformer–coupled class A amplifier has the following values:
turns ratio = 3:1
RL = 200 ,VCEQ = 6 V, ICQ = 12 mA
What is the maximum possible change in VCE for the circuit?
22)
A)
12 V
B)
Cannot be determined from the information given
C)
6 V
D)
3 V
Answer:
C
A)
B)
C)
D)
5
23)
A class A amplifier ________.
23)
A)
conducts through 360° of the input waveform
B)
conducts between 180° and 360° degrees of the input waveform, depending on the amount of
dc bias
C)
conducts through less than 180° of the input waveform
D)
conducts through 180° of the input waveform
Answer:
A
A)
B)
C)
D)
24)
A transformer–coupled class A amplifier has a transformer turns ratio of 4 : 1 and a load resistance
of 25 . The peak–to–peak value of VCE is 12 V. What is the approximate load power for the
circuit?
24)
A)
160 mW
B)
60 mW
C)
90 mW
D)
45 mW
Answer:
D
A)
B)
C)
D)
25)
The transformer–coupled class A amplifier ________.
25)
A)
can theoretically reach 60% efficient
B)
usually contains two transistors
C)
is able to provide for impedance transformation
D)
All of the above
Answer:
C
A)
B)
C)
D)
26)
Each transistor in a class B amplifier ________.
26)
A)
conducts through less than 180° of the input waveform
B)
conducts through 180° of the input waveform
C)
conducts between 180° and 360° degrees of the input waveform, depending on the amount of
dc bias
D)
conducts through 360° of the input waveform
Answer:
B
A)
B)
C)
D)
6
27)
Determine the maximum dissipation that should be allowed for a 75 W silicon transistor rated at
22° C. Derating is required above 22° C by a derating factor of 0.35 W/° C at a case temp of 142° C.
27)
A)
22 W
B)
30 W
C)
25 W
D)
33 W
Answer:
D
A)
B)
C)
D)
28)
An RC–coupled class A amplifier has values of IBQ = 1 mA, ICQ = 50 mA, VCC = 15 V,
VL= 9.3 VPP, and RL= 68 . What is the maximum efficiency of the amplifier?
28)
A)
25%
B)
21%
C)
15.9%
D)
16.6%
Answer:
B
A)
B)
C)
D)
29)
A transformer–coupled class A amplifier has a transformer turns ratio of 4 : 1 and an RL of 25 .
The peak–to–peak value of VCE is 12 V and it draws 220 mW from the dc power supply. What is
the efficiency of the circuit?
29)
A)
73%
B)
20.5%
C)
27.3%
D)
40.9%
Answer:
B
A)
B)
C)
D)
30)
The unit of measurement for thermal resistance is ________.
30)
A)
W / V
B)
/ °C
C)
· W / °C
D)
°C / W
Answer:
D
A)
B)
C)
D)
31)
The crossover distortion in a class B amplifier is prevented by ________.
31)
A)
biasing the transistors just slightly above cutoff
B)
biasing the transistors just slightly into cutoff
C)
biasing the individual transistors deeply into cutoff
D)
adjusting the load resistance so that the transistor will turn on and off faster
Answer:
A
A)
B)
C)
D)
7
32)
Crossover distortion occurs ________.
32)
A)
only in transformerless amplifiers
B)
only in class C amplifiers
C)
only in class D digital amplifiers
D)
in class B push–pull amplifiers that use complementary transistors
Answer:
D
A)
B)
C)
D)
33)
Which of the following is true?
33)
A)
The power that an amplifier delivers to a load is equal to the difference between the power
that the circuit draws from the power supply and the power that the circuit dissipates.
B)
Power amplifiers are typically used to drive low impedance loads.
C)
Efficiency is the ratio of power output to power input.
D)
All of the above
Answer:
D
A)
B)
C)
D)
34)
A given transistor has a power derating factor of 0.25 mW/°C. This transistor has a power
dissipation rating of 0.5 W at 27°C. What is the max temp the device can be allowed to operate as if
it has to dissipate 450 mW?
34)
A)
227° C
B)
190° C
C)
220° C
D)
210° C
Answer:
A
A)
B)
C)
D)
35)
A class AB amplifier has a supply voltage that is equal to +15 VDC. The value of VCE (OFF) for
either transistor is approximately equal to ________.
35)
A)
0.7 V
B)
7.5 V
C)
15 V
D)
5 V
Answer:
B
A)
B)
C)
D)
8
36)
A class D amplifier ________.
36)
A)
conducts through 180° of the input waveform
B)
conducts through less than 180° of the input waveform
C)
works only with digital and pulsed waveforms
D)
conducts between 180° and 360° degrees of the input waveform, depending on the amount of
dc bias
Answer:
C
A)
B)
C)
D)
37)
The maximum theoretical efficiency of an RC–coupled class A amplifier is ________.
37)
A)
78.5%
B)
99%
C)
25%
D)
50%
Answer:
C
A)
B)
C)
D)
38)
In a transformer–operated power amplifier, the amount of secondary load resistance that is
reflected back to the primary is ________.
38)
A)
equal to the load resistance
B)
inversely proportional to the transformer turns ratio
C)
proportional to the transformer turns ratio
D)
proportional to the square of the turns ratio
Answer:
D
A)
B)
C)
D)
9
Answer Key
Testname: C12
1)
A
2)
C
3)
A
4)
C
5)
B
6)
A
7)
A
8)
D
9)
C
10)
D
11)
C
12)
A
13)
B
14)
D
15)
D
16)
A
17)
D
18)
A
19)
D
20)
B
21)
A
22)
C
23)
A
24)
D
25)
C
26)
B
27)
D
28)
B
29)
B
30)
D
31)
A
32)
D
33)
D
34)
A
35)
B
36)
C
37)
C
38)
D