First slide

Transistor

Question

The input resistance of a common emitter transistor amplifier, if the output resistance is 500 k $Ω$ , the current gain $α =$ 0.98 and power gain is $6.0625 x 10^{6}$ , is

Moderate

A

$100 Ω$
B

$300 Ω$
C

$198 Ω$
D

$400 Ω$

Solution

$\begin{array}{l} Voltage gain, A_{v} = β \frac{R_{2}}{R_{1}} \\ Also, current gain, β = \frac{α}{1 - α} = \frac{0 .98}{1 - 0 .98} = 49 \\ A_{v} = 49 [\frac{500 \times 10^{3}}{R_{1}}] \\ Power gain = 6 .0625 \times 10^{6} = 49 \times [\frac{500 \times 10^{3}}{R_{1}}] \times 49 \\ ∴ R_{1} = 198 Ω \end{array}$

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