> The question is how do I isolate the output voltage. The
> voltage is to drive
> a 90V DC motor controller where the controller ground is live.

Use a dual optocoupler. I don't know what the term is for this circuit,
but the second coupler is put in the feedback loop on the HV side to
make the transfer independent of the coupler's characteristic, provided
that the two couplers have the same characteristic.

Or (avoid the problem instead of solving it) put the PWM signal through
an optocoupler (or trafo), do the filtering on the HV side.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads