GATE EC 2020 Set 1 — Question 54
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Analog Circuits → BJT & MOSFET Amplifiers → Biasing & DC Operating Point
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Question
In the voltage regulator shown below, is the unregulated input at V. Assume V and the base current is negligible for both the BJTs. If the regulated output is V, the value of is .
Correct answer
800 to 800
Solution
Base currents are negligible.Error-amplifier transistor (lower BJT): its emitter sits on the Zener, so . Its base is therefore atOutput divider: that base is fed from through and , with no base current drawn:( only biases the pass transistor and the error amplifier's collector; it does not enter the divider.)Answer: 800
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