Another article that might help with bench power supply designs:
To tweak supply-voltage levels and adjust voltage margins as required, this circuit introduces an op amp (MAX5481) and digital potentiometer (MAX4245) to control the feedback voltage to the voltage regulator.
Thanks rsdio!
the op amp is MAX4245 and the pot is MAX5481.
Ha!
Good catch. The original Maxim newsletter had the chips swapped in the text like that. I didn’t even notice until it was posted in the blog.
I was about to say that the problem with using a system like this for power supplies is that these digital pots are very expensive if you want lots of steps. But when I checked the price of these, only 3 dollars for 1024 steps? That is awesome!
Either way, the max voltage for the actual POT is vss +.5v so you can’t really use this for digitally controlling a SMPS feedback loop. Unless I am wrong. :P
You could be right, but take a look at the diagram. Vout goes through a voltage divider to provide Vfb, which is in turn compared to a 1.25 V reference. The op-amp and digital pot are operating at 3.3 V and yet they are perfectly capable of controlling a 5 V SMPS. I would say that with the appropriate values for R2 and R1, this circuit should work for ANY Vout. I believe that the digital pot and op-amp only have to provide 1.25 V nominally, or perhaps 2.5 V maximum. Please let me know if I’ve overlooked something, because I only just glanced at this quickly.