Question

A common emitter amplifier circuit, built using an npn transistor, is shown in the figure. Its dc current gain is $250, \,R_C = 1k\Omega$ and $V_{CC} = 10 V$. What is the minimum base current for $V_{CE}$ to reach saturation ?

• A. $100 \,\mu A$
• B. $7 \,\mu A$
• C. $40 \,\mu A$
• D. $10 \,\mu A$

Answer 1

Answer: (C)

$40 \,\mu A$

Answer 2

At saturation state, $V_{CE}$ becomes zero
$\Rightarrow i_{C} = \frac{10V}{1000\Omega} = 10 mA$
now current gain factor $\beta = \frac{i_{C}}{i_{B}}$
$\Rightarrow i_{B} = \frac{10mA}{250} = 40 \mu A$