JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Semiconductors

An NPN transistor is used in common emitter configuration as an amplifier with

1 k Ω

load resistance. Signal voltage of 10 mV is applied across the base-emitter. This produces a 3 mA change in the collector current and

15 μ A

change in the base current of the amplifier. The input resistance and voltage gain are:

Answer: (A)

Solution

The input resistance is the ratio of the signal voltage across the base-emitter to the base current it drives:

r_{in} = \frac{10 \times 1 0 ^{- 3}}{15 \times 1 0 ^{- 6}} \approx 667 Ω \approx 0.67 k Ω

. The output voltage across the

1 k Ω

load is

i_{c} R = 3 \times 1 0^{- 3} \times 1000 = 3

V, so the voltage gain is

\frac{3}{10 \times 1 0 ^{- 3}} = 300

JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Single correct option