I've been using the National "Simple Switchers" with good results for
awhile, and would like to take a step beyond the usual methods of setting
the output voltage. I typically use the fixed voltage versions of the LM2676
with a resistor in series with R2 to increase the output voltage when the
predetermined +5 or +12 needs adjusted. But now I'd like to control the
output voltage using a microcontroller. I'm pretty sure I could get this
done by using the adjustable version which does not have R1 or R2, and
placing a digital potentiometer in place of R1 with an appropriate value of
fixed resistor for R2. However, I have a spare channel from an offboard 5
volt D/A which would be cheaper and easier from a BOM standpoint. I was
hoping to get it done with some spare R to R opamps which are also
available.

My analog skills have gotten a little lazy over the years and I'm having a
tough time thinking this one out. I guess the bottom line is that I need to
control the feedback current from the switcher output using a 0-5v DAC
output.

Any ideas? I would tend to think this has already been done somewhere by
someone...

Chris