> > I need to be able to switch power to a section of my circuit off and on
> > under PIC control. I've been looking at analog switches, but they all
> > have fairly high "on" resistance (tens of ohms or more). The problem is
> > that I need to provide a nicely regulated 5V at a widely varying current
> > (fraction of a mA up to 100 mA) when the power is on. Even a 10 ohm
> > resistance will drop the voltage significantly at those high currents.
>
> I think that you want a VFET. Try a BSS (BSS 170 etc).
>
> Peter

A highly-saturated medium power PNP transistor in series with the supply
(emitter to unswitched) in a common base configuration works well.  Use
a VFET to switch the base to ground (through a resistor).  This
configuration only drops a few tenths of a volt.

Or, National Semi make a few switchable low dropout regulators - check
their web site. I've used the LP2957 but it may not satisfy your output
requirements.

--Matt