Cutoff voltage for FETs

Started by ildar, February 11, 2006, 11:23:52 PM

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ildar

Is there a general voltage-high and/or low at which FETs cease to function?
Does it vary by type or by individual piece? Do the other components have some bearing on it? (probably...)
I want to set my Thunderchief at a lower voltage for "mush", and was wondering how low is too low?

R.G.

Yes. There is a voltage between the gate and source at which it passes no more current. This is called Vsgoff. If you are talking about the voltage between drain and source, there is a parameter called the pinch off voltage, Vp. This is the voltage at which the JFET passes from being a voltage controlled resistor into being a voltage controlled current source. It's on the order of 1-4V depending on the JFET.

Like all JFET parameters, there is a big spread of Vgsoff and Vp within the same type number, and even a bigger spread across type numbers.

How low is too low? A volt or two. It won't hurt the JFET, it'll just quit amplifying.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

ildar

#2
Thanks R.G.
I was also wondering if it would harm the jfet-no sense in burning them out.