piclist 2003\02\13\123909a >
Thread: MOSFET as a digital switch
www.piclist.com/techref/index.htm?key=mosfet+digital+switch
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face BY : Ned Konz email (remove spam text)



On Thursday 13 February 2003 09:09 am, you wrote:
> All this talk of FET's is bringing back some fuzzy memories of it
> when in class.  Thats what happens when you just do digital design
> for years.
>
> These are bidirectional devices right? Such that it doesnt matter
> if the load is attached to the drain or source? Or does it matter?

Yes, because there is a "body diode" between D and S.

On a N-channel device, the body diode will conduct (even if the
transistor is OFF) when the S becomes more than a little positive
than the D.

P channel devices are reversed from that.

So when there's a real bidirectional current flow requirement, people
tend to use two FETs with their diodes back to back.

--
Ned Konz
http://bike-nomad.com
GPG key ID: BEEA7EFE

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