Q. Explain the drain characteristics of JFET with external bias?
It gives relation between Id and Vds for different values of Vgs.(which is called the running variable). The above drain characteristic graph can be used for explanation.
It is seen that as the negative gate bias voltage is increased:
(i) pinch off voltage Vp is reached at a lower value of Vds than when Vgs=0.
(ii) value of Vds for breakdown is decreased.
It is seen that with Vgs=0,Id saturates at Idss and the characteristics shows Vpo=5v When an external bias of -1v is applied ,gate-channel junction still require -5v to achieve pinch-off .It means that Vds=4v is now required instead of previous 4v.