Question

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

Answer 1

A transistor is a semiconductor device which is commonly used as a switch in electronic circuits and as an amplifier. It consists of three regions called Emitter, Base and Collector. The charge-carriers originate in the Emitter region and travel across the Base to the Collector region.

Here ∆Ib = 10 µA = 10 x 10^-6 A

∆Ic = 2 mA = 2 x 10^-3 A

Ri = 1000 Ω, RL = 5000 Ω

(i) Now ß = \(\frac{\bigtriangleup I_c}{\bigtriangleup I_b} = \frac{2 \times 10^{-3}}{10 \times 10^{-6}}\) = 200

(ii) A_V = ß \(\frac{R_L}{R_i} = 200 \times \frac{5000}{2000}\)

or A_V = 1000