Don't forget you can get 5 volt regs with logic shutdown control such as
LM2925

        cya,    Andrew...

> -----Original Message-----
> From: Jinx [SMTP:joecolquitt@CLEAR.NET.NZ]
> Sent: Friday, November 12, 1999 5:06 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [OT]How to make high side switch
>
> There are any number of ways to control 12V by 5V.
>
> For example use the PIC to drive an npn TR to ground the base of a
> pnp power TR whose base is normally held high by a  resistor (the
> pnp's emitter is also connected directly to 12V), the 12V coming out
> of the pnp collector into the reg.
>
> Or an optocoupler, driving the LED side with the PIC, the TR side
> driving either a power TR, FET or reg directly
>
> Or a 5V-12V level shifter, eg ICL7667 to drive a power FET
>
> Or even an RS232-type or bus level shifter (you may have one lying
> around)
>
> etc etc etc
>
> A lot depends on what current you'll be expecting to put through the reg
>
> Jinx