A common emitter amplifier circuit, built using an npn transistor, is shown in the figure. Its dc current gain is 250, RC = 1k Ω and VCC = 10 V. What is the minimum base current for VCE to reach saturation? (a) 100 μ A (b) 7 μ A (c) 10 μ A (d) 40 μ A

Answer: (d). At saturation VCE ≈ 0: IC = VCCRC = (10 V)/(1 kΩ) = 10 mA Minimum base current: IB = (IC)/(β) = (10 mA)/(250) = 40 So the answer is (d) 40.

A common emitter amplifier circuit, built using an npn transistor, is… | JEE Main 2019 (8 Apr, Shift 2)

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Junction Transistor

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

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Answer: (d)

At saturation $V_{CE} \approx 0$ : $I_C = \dfrac{V_{CC}}{R_C} = \dfrac{10\ \text{V}}{1\ \text{k}\Omega} = 10\ \text{mA}$
Minimum base current: $I_B = \dfrac{I_C}{\beta} = \dfrac{10\ \text{mA}}{250} = 40\ \mu\text{A}$
So the answer is (d) $40\ \mu\text{A}$ .

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