The GATE Grind

GATE 2023 EE – Question 59

Analog and Digital Electronics · Amplifiers: biasing, equivalent circuit and frequency response · 2 marks · Numerical answer

The Zener diode in circuit has a breakdown voltage of 5 V. The current gain $\beta$ of the transistor in the active region is 99. Ignore base-emitter voltage drop $V_{BE}$. The current through the 20 Ω resistance in milliamperes is ________ (Round off to 2 decimal places).

Diagram for GATE 2023 EE question 59

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 248.75 to 251.25

Explanation

The Zener holds the base at 5 V and, with $V_{BE}$ ignored, the emitter is also at 5 V. The current in the 20 Ω emitter resistor is $5/20=250$ mA. (The base current is $250/100=2.5$ mA, which the 7 kΩ resistor supplies: $(25-5)/7\text{ k}=2.86$ mA, leaving a small current in the Zener.)