Question

Describe operation of N-channel JFET

Answer 1

Operation of N-channel JFET 

1) When VGS = 0 volt: When a voltage is applied between the drain and source with a DC supply voltage VDD with VGS = 0 V, the electrons flow from source to drain through the narrow channel existing between the depletion regions. This constitutes drain current ID. The value of drain current is maximum when VGS = 0 V. This current is designated by the symbol IDSS. 

2) When VGS is negative: When VGS is increased below zero i.e negative, the reverse voltage across the gate source junction is increased. As a result depletion regions are widened. This reduces effective width of channel and therefore controls the flow of drain current through the channel. If VGS is increased further, two depletion regions touch each other. The drain current reduces to zero. The gate to source voltage at which current reduces to zero is called as pinch-off voltage.