Question

What is the relation between the drain current and source current once the voltage crosses pinch off?

(a) ID = IS

(b) ID = IS + 1.5

(c) ID = 1/IS

(d) IS – 2ID = 0

This question was addressed to me during an interview for a job.

My question is from The Pinch off Voltage Vp in portion Field-Effect Transistors of Electronic Devices & Circuits

Answer 1

Right answer is (a) ID = IS

Explanation: For a FET, once the voltage exceeds the pinch off voltage, the electrons will start flowing from source to drain or vice versa, since no current flows through the gate terminal, the current transfer takes place only between the drain and source. Hence ID = IS.