# Confusion regarding pinch off voltage in a JFET

1. Jan 22, 2014

### smatik

I can't figure out what actually is the Pich-off voltage of a JFET.
I basically have confusion between these two definitions:
1. Pinch off voltage is that gate source voltage at which there is no drain-source current
2. Pinch of voltage is that 'Drain-Source' voltage after which the drain source current becomes almost constant(saturates).
If there is some other accurate definition for pinch off voltage,Please tell me.
Also i want to ask that what is pinch off region?
Thanks

2. Jan 22, 2014

### Jony130

Here you find answer what is pinch off region.
http://www.electronics-tutorials.ws/transistor/tran_5.html

So the proper definition of a Pich-off voltage is
Pinch of voltage is that 'Drain-Source' voltage after which the drain source current becomes almost constant(saturates).
And for n-channel JFET Pich-off voltage is positive. But because Vgs(off) (the gate source voltage at which there is no drain-source current) voltage is negative and by accident equal to the magnitude of the pinch off voltage. Hence:
|Vgs(off)| = |Vp| the magnitude of the pinch off voltage is equal to Vgs(off).
And this is why we can say that |Vp| = |Vgs(off)| but in the same time Vp is a saturation voltage.
But the only difference is the minus sign. Because Vgs(off) is negative but Vp is positive.