> why do you need the pic? cant you just use like a few capacitors, a
> rectifier (or 4 diodes, depending) a LM317
Been there, done that, got the T-shirt, wore it out, sold it to Goodwill.
LM317's are simple, but they won't handle more than an amp, won't dial down
to less than 1.2 volts, pots are hard to adjust in tiny increments, and
LM317's are linear so they waste lots of power.  I've prolly built a dozen
supplies with them.

You won't get 5 amps out of an LM317 without a bunch of extra parts.

I built a nice little bench supply with a PIC running a P-Channel pass
transistor, threw in an inductor and a capacitor and two pushbutton inputs
to the PIC.  The PIC senses output voltage, and turns the pass transistor on
and off.  The two pushbutton inputs run the setpoint up and down.  A little
digital panel meter serves as the interface, you just push the UP button if
you want the voltage higher, etc.  None of the part values seemed to be very
critical, worked pretty good first time with junk parts off my bench.

Running behind a stable 24V power source it seems to give pretty good
regulation and will provide lots of current if required, will dial down to
less than .25 volts, and can be adjusted in micro-increments.  Used a 16F873
so I could use the 10 bit A/D for lots of fine adjustment.

Of course there are 1000 circuits using LM317's plus pass transistors.  I
just wanted to build a switcher with a PIC in it, so I could slap a sticker
on it saying "PIC INSIDE!"

--Lawrence

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