in insulated-gate field-effect transistors (IGFET), "pinch-off" refers to the channel pinching that leads to current saturation behaviour under high source–drain bias. in junction field-effect transistors (JFETs), "pinch-off" refers to the threshold voltage below which the transistor turns off.
Consequently, what is Pinchoff voltage in JFET?
Pinch off voltage: Pinch off voltage is the drain to source voltage after which the drain to source current becomes almost constant and JFET enters into saturation region and is defined only when gate to source voltage is zero.
Why VGS is negative in JFET?
The control of the Drain current by a negative Gate potential makes the Junction Field Effect Transistor useful as a switch and it is essential that the Gate voltage is never positive for an N-channel JFET as the channel current will flow to the Gate and not the Drain resulting in damage to the JFET.