Draw a circuit diagram for use of n-p-n transistor as an amplifier in common emitter configuration. The input resistance of a transistor is 1000 Ω. On changing its base current by 10 μA, the collector current increases by 2 mA. If a load resistance of 5 kΩ is used in the circuit, calculate:
(i) the current gain,
(ii) voltage gain of the amplifier.

Solution

Circuit of n-p-n transistor as an amplifier in common emitter configuration is given below:

Numerical:

Given,

Change in base current, ∆ I_{B} = 10 μA Change in collector current, ∆ I_{C} = 2 mA Load resistance, R_{L} = 5 kΩ Input resistance, R_{i} = 1 kΩ

(i) The current gain is given by,

β = {(\frac{∆ I_{C}}{∆ I_{B}})}_{V_{CE}} = \frac{2 \times 10^{- 3}}{10 \times 10^{- 6}} = 200

(ii) Voltage gain is,

A_{V} = β \times \frac{R_{L}}{R_{i}} = 200 \times \frac{5}{1} = 1000 .

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