Jon Petty wrote:

> Hi
>
> I am trying to find the best way to make a high side switch to control an
> auxillary power source for my pic in an automotive application. When ignition
> switch voltage is present (13.8V or so) I want the pic to control a switch
> that will direct 12V battery power to the  5V regulator for perifferals. When
> ignition switch is off,  high side switch will cutoff bat supply to 5V
> regulator for perifferals.
>
> I would like a logic level signal from pic to control 12V source to regulator.
>
> My plan was to use a pnp mosfet.

You mean a P-channel?

> It said it was a logic level hexfet, but it did not work.

They work for me!  I'll bet you didn't use correct gate drive.
Source to battery, gate must go from battery level (Off) to a TTL level or great
er
less than battery. (On)
The PIC can't source battery level voltage without a buffer. (FET)  Or open drai
n
high voltage output.

> I tried an npn logic level mosfet and it didn't work either. It
> appeared the gate logic was dependent on the batter voltage. I got a  pnp
> transistor to work when gate voltage was above or below the batt voltage, but
> it was the inverse of what I was looking for. I know I am missing something
> simple.
>
> It seems so simple I have done it in the past using 5v relays, but I thought
> there must be a simplier SS solution .
>
> Could you provide some suggestions on how I can make a logic level high side
> switch cheap?
>
> Thanks
>
> Jon

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
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