>
> My plan was to use a pnp mosfet. It said it was a logic level hexfet, but it
> did not work. I tried an npn logic level mosfet and it didn't work either.

Logic Level means that the switching (fully on channel) voltage on
the gate is around 5 volts... often 3 volts as well ( as opposed to
the 11 volts needed on a typical mosfet). This is easy to understand
with an N channel.... 0 volts =off, 5 volts =on  at any appropriate
voltage on the drain. BUT....... a P channel logic level mosfet is
off at VCC and on at VCC - 5volts.... e.g. at 12 volts vcc 12 volts
on the gate will turn it off, 7 volts or less will turn it on!!!!!
I usually use a low power logic level N channel mosfet from the pic,
the drain of the N channel has a resistor.. say 100K from 12 volts
(in this example) to the mosfet drain, this provides a 0 to 12 volts
swing at is drain that I can connect onto the gate of an ordinary P
channel power mosfet.
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Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

www.psych.auckland.ac.nz

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