Actually, check your facts.. I don't ever want to argue on this forum, but I
just pulled an old text from the shelf, and it clearly explains how IN
THEORY, MOSFET's, both N & P channel will work with either positive or
negative gate bias. I have tested this years ago and found it to be true in
SOME cases, not so in others. What you mention is the normal application,
and some devices will not work both ways. Then, of course there is the
interal diode to consider...Well, Russ, I guess you didn't write all the
books...

But I did say that I refuse to argue just wanted to clear this up.

> > Theoretically, unlike the JFET or IGFET, MOSFET's, whether
> N or P channel
> > can be driven with either + or - Vg. That would imply bidirectional
> > application.
>
> Not quite, I'm afraid.
> An enhancement mode MOSFET (by far the most normal type)
> (never actually
> seen a depletion mode MOSFET) is on when -
>
> - For an N channel, the Gate is more positive than the Source.
> - For a P channel, the Gate is more negative than the Source
>
> by a suitable voltage level (see spec sheet) in each case.
>
> In both cases the FET will then conduct resistively and bidirecionally
> between Drain and Source.
>
> However,, as others have noted, there is in each case a
> reverse "body diode"
> across Drain & Source which is an inherent part of the FET
> and cannot be
> eliminated. This will conduct when the FET is reverse biases
> Drain to Source
> even if the FET is off.
>

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