1
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What
is meaning of the transistor?
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Transistor
- The transistor is a three terminal semiconductor
device in which one type of semiconductor material (either P or N) is
sandwich between other types of semiconductor material (either N or P) of
opposite polarity.
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2
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Why the transistor is called as
Bipolar junction transistor?
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Bipolar
junction transistor
- The current conduction is
the transistor is done by holes as well as electrons therefore it is called
as Bipolar junction transistor.
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3
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Describe the main function of the
transistor.
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To amplify weak signal
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4
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How many PN junction the transistor
consists of?
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Two
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5
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How many terminals the transistor
consists of?
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Three terminals – Emitter,
Base and Collector
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6
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Why the collector terminal is made
larger than the emitter and base?
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Because most of the heat
produced across collector junction
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7
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Whether the holes or electrons are
responsible for collector cut off current in the transistor?
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- The collector cut off
current flows due to minority charge carriers. The collector cut off current
flows due to holes in the NPN transistor and electrons in the PNP transistor.
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8
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What are the doping levels in the
transistor?
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The transistor consists of three terminals.
Emitter
- The emitter is heavily doped therefore it supplies
large numbers of charge carriers to the base and collector of the transistor.
Base
- The base is lightly doped and very thin, therefore
only small current passes through the base.
Collector
- The collector is moderately doped therefore the most
of the current passes through it which is supplied by the emitter. The
emitter current ( IE ) is sum of the base current ( IB )
and collector current ( IC ).
IE = IB + IC
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9
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Explain : Current amplification factor
α
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Current amplification factor α
- The ratio of change in collector current to the
change in emitter current at constant collector base voltage in the Common Base
transistor is known as current amplification factor.
α = dIC / dIE at
constant VCB
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10
|
Explain : Current amplification factor
β
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Current amplification factor β
- The ratio of change in collector current to the
change in base current at constant collector emitter voltage in the Common
Emitter transistor is known as current amplification factor.
β
= dIC / dIB at constant VCE
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11
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Explain : Current amplification factor γ
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Current amplification factor γ
- The ratio of change in emitter current to the change
in base current at constant collector emitter voltage in the common collector
transistor is known as current amplification factor.
γ
= dIE / dIB at constant VCE
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12
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Describe the different configurations
are used in the transistor.
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Different configuration of the transistor
- As the transistor consists of three terminals. The
transistor must be one common terminal in order to supply input and get
output of the transistor. The following
three types of configurations are used in the transistor
Common emitter (CE) configuration
Common base (CB) configuration
Common collector (CC) configuration
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13
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What is practical value of α and β?
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- The practical value of α is in the range of 0.9 to
0.99 and β is in the range of 20 to 500. The value of α is increased by
making base thin and lightly doped.
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14
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Explain : Bias voltage. Describe the function
of bias voltage in the transistor.
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Bias voltage
- The DC voltage at the input side of the transistor
is called as bias voltage.
- The emitter base circuit is always forward biased
for faithful amplification.
- The emitter base becomes reverse biased during
negative half cycle of the signal without bias voltage.
- Therefore magnitude
of the bias voltage should be such that it always keep the emitter base
circuit forward biased.
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15
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What is ICBO?
OR
What is meant by collector leakage
current in the transistor?
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Collector
leakage current
- The flow of the collector current while input or
emitter circuit kept open circuited in the common base transistor is called
as collector leakage current. It is donated by ICBO.
OR
- The flow of the collector current while input or
base circuit is kept open circuited in the common emitter transistor is
called as collector leakage current. It is donated by ICEO.
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16
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Write the relation between current amplification
factor α and β
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Relation
between current amplification factor α and β
β = α / (1 – α )
OR
α = β / ( 1 + β )
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17
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What is zero signal collector current
in the transistor?
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Zero
signal collector current
- It is defined as the collector current flows when
the input circuit of the transistor is forward biased by only battery or
direct voltage.
OR
- It is defined as the flow of collector current when
no signal is applied, the input circuit is forward biased by battery or
direct voltage.
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18
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Describe the main factor affecting
value of collector leakage current.
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Factor affecting collector leakage current
- The value of collector leakage current is neglected
in the low power transistor whereas it is in the range of micro – ampere for
high powered transistor.
- The collector leakage current depends upon the
temperature and its value increases rapidly with increase in the temperature.
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19
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Explain the term : Cut off region, Saturation region, Active region
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Cut off region
- The transistor is operated in the cut off region
when base current is equal to zero.
Saturation region
- The collector and emitter terminal of the transistor
are shorted together. The transistor behaves like closed switch between
collector and emitter.
Active region
- The region between cut off and saturation is called
as active region of the transistor.
- The
base – emitter of the transistor always forward biased whereas the collector
– base junction remains reverse biased in this region under all conditions.
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20
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Describe the working of two back to
back diodes in the cut off, active and saturation region of the CE
transistor?
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Status of back to back diode in the transistor
- Cut off : Emitter diode OFF, Collector diode OFF
- Active : Emitter diode ON, Collector diode OFF
- Saturation : Emitter diode ON, Collector diode ON
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