Drain characteristics:-
As VDS is increased from zero as shown , ID will increased proportionally through the p channel. In this region the channel resistance is constants because the depletion region is not large enough to have significant effect. This is called the “Ohmic region” because VDS & ID are related by ohm’s law.
As point B, the curve level off & ID becomes essentially constants.
As VDS increases from point B to C the reverse bias voltage from gate to drain (VGD) produces a depletion region (i.e. channel resistance). It is proportional to the increase in the VDS so the current ID practically constant at IDSS. The value of VDS at which ID becomes essentially constant is the pinch off voltage (VP).
Breakdown occurs at point C. when ID begins to increase very rapidly with any further increase in VDS. So JFET’s are always operated below breakdown & within constant current region,
As VGS is set increasing, more positive value by adjusting VGG. ID decreases as the magnitude of VGS is increased because of narrowing width of channel.
The maximum value of VGS at which drain current reaches to zero due to overlapping both the depletion layer. (i.e. channel width zero) is called cutoff voltage or VGS(off).