Correct Answer - Option 1 : 49
Concept:
\(\beta = \frac{\alpha }{{1 - \alpha }}\)
Where,
β = common-emitter current gain
α = Common base current gain
Calculation:
Common base current gain = α = 0.98
\(\beta = \frac{{0.98}}{{1 - 0.98}} = 49\)
Note:
\(\alpha = \frac{{{I_C}}}{{{I_E}}}\) & \(\beta = \frac{{{I_C}}}{{{I_B}}}\)
Where IC = Collector current
IE = Emitter current
IB = Base current
The DC current gain of a common collector is therefore given by the ratio of emitter current to the base current, i.e.
\(\gamma=\frac{I_E}{I_B}\)
IE = Emitter Current
IB = Base Current
Also, IE = IB + IC
DC current gain will be:
\(\gamma=\frac{I_C+I_B}{I_B}=\frac{I_C}{I_B}+1\)
The DC current gain for a common emitter configuration is defined as:
\(\beta=\frac{I_C}{I_B}\)
Equation (1) now becomes:
\(\gamma=\beta +1\)
Important Differences between different transistor configuration is as shown:
|
Parameter
|
Common-Base
|
Common-Emitter
|
Common-Collector
|
|
Input Current
|
IE
|
IB
|
IB
|
|
Output Current
|
IC
|
IC
|
IE
|
|
Current Gain
|
\({α _{dc}} = \frac{{{I_C}}}{{{I_E}}}\)
|
\({\beta _{dc}} = \frac{{{I_C}}}{{{I_B}}}\)
|
\(\gamma = \frac{{{I_E}}}{{{I_B}}} = \left( {1 + {\beta _{dc}}} \right)\) |
|
Voltage Gain
|
Medium
|
Medium
|
Less Than 1
|
