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1
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Describe the function of the voltage
amplifier.
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Voltage amplifier
- The function of the voltage amplifier is to raise
the voltage level of the input signal to desired value.
- The first stage of
the multistage amplifier should be voltage amplifier.
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2
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Describe the function of the Power
amplifier.
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Power
amplifier
- The function of the Power amplifier is to raise the
power level of the input signal to desired value.
- The last stage of the
multistage amplifier should be power amplifier.
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3
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What is range of frequencies that
human ear can hear?
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The human ear can hear the range of audio frequency
from 20 Hz to 20 kHz.
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4
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Describe the main difference between
small signal amplifier and large signal amplifier.
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Small signal amplifier
- Small alternating input signal
- It operates in the linear portion of the output
characteristics.
- No distortion in the output.
Large signal amplifier
- Large alternating input signal.
- It produces large alternating power output.
- The main function of the large signal amplifier
impedance matching.
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5
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Explain the term : Collector efficiency.
Describe the importance of it.
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Collector efficiency
- The ratio of the AC power output to the DC input
power is known as collector efficiency.
- If the input DC power is 20 W and
output AC power is 10 W, the collector efficiency is 50%.
- The collector
efficiency must be higher in order to achieve large output power.
- The power
amplifier converts DC input power in to AC output power.
- Therefore the
collector efficiency measures the effectiveness of the power conversion from DC
to AC.
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6
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Explain the term : Distortion
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Distortion
- When the shape of the output signal is not exactly
same at that of input signal, it is called as distortion.
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7
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Give reason : The distortion in the
power amplifier is critical than that of voltage amplifier.
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The power amplifier handles large current whereas
the voltage amplifier handles only small signals therefore the distortion is
very large in the power amplifier as compared to voltage amplifier.
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8
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How the power amplifiers are
classified?
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Classification of power amplifier
Class A amplifier
- If the biasing of the power amplifier must be such that the
collector current flows for full cycle, it is known as class A amplifier.
Class B amplifier
- If the biasing of the power amplifier must be such
that the collector current flows only during positive half cycle, it is known
as class B amplifier.
Class C amplifier
- If the biasing of the power amplifier must be such
that the collector current flows only less than half cycle, it is known as
class C amplifier.
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9
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Describe the disadvantages of the
class A power amplifier.
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Disadvantages of class A power amplifier
- Low collector efficiency
- Low power output
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10
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Which type of power amplifier has very
less distortion?
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The output signal of the class A power amplifier is
exactly same as that of input signal therefore class A amplifier produces
very low distortion.
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11
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Describe the advantages of the class B
power amplifier.
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Advantages of the class B power amplifier
- High collector efficiency
- High power output
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12
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Which type of power amplifier works as
half wave rectifier?
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Power
amplifier as half wave rectifier
- The operating point in the Class B power amplifier
is selected such that during positive half cycle, the input circuit becomes
forward biased and output circuit becomes reverse biased.
- Therefore the
collector current flow only for positive half cycle.
- The input circuit becomes reversed biased during negative half cycle resulting collector current
does not flow. Therefore the class B amplifier works as half wave
rectifier. .
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13
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Which type of amplifier never used in
the power amplification?
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Class C power amplifier
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14
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Describe the application of the class
B and class C power amplifier.
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The class B power amplifier is used for power
amplification in the push pull arrangement whereas the Class C power
amplifier is used as tuned amplifier.
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15
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Explain the term : Driver stage
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Driver
stage
- The stage between voltage amplifier and power
amplifier is known as the driver stage.
- The output of last stage voltage
amplifier is given to the input of the driver stage and output of the driver
stage is connected to the input of the power stage.
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16
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Describe the function of the driver
stage.
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Function
of driver stage
- The function of the driver stage is to impedance
matching and transfer maximum power.
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17
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Which type of transformer is used in
the driver stage of the power amplifier? Step up transformer or step down
transformer
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Step down transformer
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18
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Why the centre tapping transformer is
used in the driver stage of the power amplifier?
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The output of the centre tapping transformer is
connected to the input of the push pull amplifier.
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19
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What is push – pull amplifier?
OR
How class B amplifiers are employed to
produce high efficiency?
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Push – Pull
amplifier
- The two class B power amplifier in the Push – Pull arrangement
is connected such that one amplifier amplify only positive half cycle of the
input signal whereas the other amplifier amplify negative half cycle of the
input signal.
- Therefore such an arrangement produces complete sinusoidal
waveform or it is called as Push – Pull amplifier.
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20
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Describe the function of transformer
in the transformer coupled power amplifier.
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Function
of transformer in the power amplifier
- Impedance matching
- To keep small DC power
loss due to small resistance of the primary winding
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21
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At which condition, the power
dissipation in the class A power amplifier?
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Zero signal condition
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22
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Describe the advantages and
disadvantages of complementary symmetry amplifier
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Advantages
- No center tap transformer
requires
- Low weight and cost
Disadvantages
- Two supply source requires
- It is quite difficult to
get pair of NPN and PNP transistor having same characteristics.
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