RussellMc wrote:
>>
http://www.electro-tech-online.com/attachments/electronic-projects-design-i=
deas-reviews/18890d1209004583-lm317-control-pic-mcu-lm317.png
>
> Looks entirely workable - essentially what I described.

If you're going to go so far as adding a opamp to control the LM317, you
might as well just have the opamp drive something like a PNP pass
transistor.  The fancy electronics in the LM317 isn't doing much for you at
this point.  You're mostly using the LM317 as a pass element anyway.

Stability might be a little better with the '317 since things can be
arranged to be more linear, but you have to think about stability in either
case, and it's not that hard to drive a PNP or PFET directly.

Again though, does the PWM high side really need to be varied at all?  It
would be simpler and more efficient if this modulation could be performed
with duty cycle control and the LM317 dispensed with altogether.  If the
user input via the pot still needs to be there, wire the pot between the PI=
C
Vdd and Vss driving a A/D input, then have the result modify the duty cycle
inside the PIC.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.