If you use the PIC to do the ADC it will be susceptible to the same voltage fluctuations as the DtoA output. You would need to use a voltage reference chip for accuracy so why not just power the PIC from a voltage reference and that would govern the AtoD accuracy. On 12 April 2012 22:25, Richard Prosser wrote: > Hi Neil, > > On 13 April 2012 00:26, Neil wrote: >> What exactly do you mean by "clamping the output"? =A0I actually need 0.= 5V >> to 4.5V output, and Vdd will be 5V. =A0But I was looking for the A/D >> feedback,etc for accuracy, since the PWM voltage output will be subject >> to variations in Vdd. >> >> Cheers, >> -Neil. >> > > Basically I was thinking about a system where the output voltage was > limited to, say, 4.5V by means of a series resistor & precision zener > / TL431 etc. This would then be independent of supply voltage but > subject to any temperature drift in the clamping device. The minimum > voltage would be close to zero - if you need it to be 0.5V, then you'd > need to add it in - use an opamp circuit to provide the clamping > function with a 0.5V offset.? > > RP > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .