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Electronic Devices and Circuits

Q1: Assertion (A): A JFET behaves as a resistor when VGS < VP. Reason (R): When VGS < VP, the drain current in a JFET is almost constant.

A Both A and R are true and R is correct explanation of A

B Both A and R are true but R is not a correct explanation of A

C A is true but R is false

D A is false but R is true

ANS:C - A is true but R is false

Pinch off voltage is the drain to source voltage after which the drain to source current becomes almost constant and JFET enters into saturation region and is defined only when gate to source voltage is zero.

If the last condition is not satisfied then the voltage will not be called pinch off voltage even though after it drain to source current becomes constant.

Current attain saturation value because all the free electrons (or holes) are able to reach from source to drain and thus there is no increase in charge carrier density and hence the current in-spite of increase in drain to source voltage.

Vgs (off) is the gate to source voltage at which drain current becomes zero because of the spreading of depletion layer, which in turn reduces the length of conduction channel. P.S: The numerical value of both pinch off and Vgs (off) is same.



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