First slide

Transistors

Question

An n – p – n transistor is used in common emitter configuration with an amplifier with $1 k Ω$ load resistance. Signal voltage of 10 mV is applied across the base – emitter. This produces a 3mA change in the collector current and 15 $μ A$ change in the base current of the amplifier. The input resistance and voltage gain are

Moderate

A

$0.67 k Ω, 200$
B

$0.33 k Ω, 1.5$
C

$0.67 k Ω, 300$
D

$0.33 k Ω, 300$

Solution

$∴ V o l t a g e g a i n = \frac{V_{o u t p u t}}{V_{i n p u t}}$
$= \frac{R_{l} \times △ I_{c}}{V_{i n}}$
$= \frac{1 \times 10^{3} \times 3 \times 10^{- 3}}{10 \times 10^{- 3}} = 300$
$I n p u t R e s i s \tan c e : R_{i n} = \frac{V_{i n}}{i_{i n}} = \frac{V_{i n}}{i_{b}} = \frac{10 \times 10^{- 3}}{15 \times 10^{- 6}}$
$= \frac{10 \times 10^{3}}{15} = 0.67 \times 10^{3} Ω = 0.67 k Ω$

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