The main difference between the JFET and a BJT device is that when the JFET junction is reverse-biased the Gate current is practically zero, whereas the Base current of the BJT is always some value greater than zero.

Why is gate current zero in a JFET?

The gate-to-source voltage is used to control the depletion region of the JFET. At first, is set to zero; the depletion region on both sides is formed. ... The input current is always zero as the gate-to-source junction is never forward biased. Hence, the current is effectively for a JFET transistor.

How does current flow in JFET?

Field-effect transistors control the current between source and drain connections by a voltage applied between the gate and source. In a junction field-effect transistor (JFET), there is a PN junction between the gate and source which is normally reverse-biased for control of source-drain current.