Question

In JFET, drain current is primarily controlled by ________.

• A. Size of depletion region
• B. Channel resistance
• C. Gate reverse bias
• D. Voltage drop across the channel

Hint:

Gate reverse bias controls drain current in JFETs because it modulates the channel width via depletion region control.

Answer 1

The Correct Option is C

In a Junction Field Effect Transistor (JFET), the gate is always reverse-biased. This reverse bias controls the width of the depletion region, which in turn narrows or widens the conductive channel. The narrower the channel, the less current can flow through from drain to source.
The reverse bias on the gate voltage (\(V_{GS}\)) directly controls the depletion width, and thus: \[ I_D = I_{DSS}\left(1 - \frac{V_{GS}}{V_P}\right)^2 \] This is the Shockley's equation for JFETs in saturation. Clearly, gate reverse bias is the controlling parameter. 
Final Answer: (3) Gate reverse bias