Common Circuit Application(Voltage-Controlled Resistor)

V_GS must be between zero and V_GS.off .

Common Circuit Application(Source Follower)

The simple source follower is shown below. The improved version is shown at the right. The lower JFET forms a current source. The result is that V_GS is held constant, removing the defects of the simple circuit.

Common Circuit Application(Current source)

The drain current is set by R_S such that V_GS = I_DR_S. Any value of current can be chosen between zero and I_DSS.

Common Circuit Application(Voltage Controlled Switch)

For the on state the gate voltage V_GS = 0 and for the off state |V_GS| > |V_GS.off| (of greater magnitude then V_GS.off and with the same sign). The sign of the voltage depends on the type of FET, negative for n-channel and positive for p-channel.