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GATE 2014 EC (EC3) – Question 47

Analog Circuits · BJT and MOSFET Amplifiers · 2 marks · Multiple choice

The silicon BJT shown has β = 50, V_BE = 0.7 V and V_CE(sat) = 0.2 V. Which statement is correct?

Diagram for GATE 2014 EC (EC3) question 47
  1. For R_C = 1 kΩ, BJT is saturated.
  2. For R_C = 3 kΩ, BJT is saturated.
  3. For R_C = 20 kΩ, BJT is cut off.
  4. For R_C = 20 kΩ, BJT is in the linear region.

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Show answer and explanation

Correct answer: (B) For R_C = 3 kΩ, BJT is saturated.

Explanation

The base current is(5−0.7)/50kΩ=86µA. Active-mode collector current would beβIB=4.3mA. For RC=3kΩ the maximum current with VCE,sat=0.2V is(10−0.2)/3kΩ=3.267mA, below4.3mA, so the BJT saturates. Therefore **B**. RC=1kΩ permits active operation; positive base drive prevents cutoff at20kΩ.