On Sun, May 29, 2011 at 6:41 PM, Denny Esterline wro= te: > A shunt resistor in the gnd line is easy because it's the same gnd as the > rest of the sensing circuit - you don't have to level shift the signal > (which can be a pain). > The downside is... well there's several, but the one that always bugged m= e > is now the negative output terminal, your load connection point, is now s= ome > value above ground - a variable value dependent on current at that. Lots = of > loads don't mind, some do. It's a recipe to create weird ground loop > problems when you hook up a scope probe or serial port to a PC. > I don't see why putting a shunt resistor in the negative line is a problem at all. Most power supplies (at least of the lab or bench variety) have ground-isolated outputs. I would just take care to make sure that no points in my circuit on the isolated side of the input transformer were connected to earth or chassis ground. Then, if I am careful to run the reference for my regulator right to the negative output terminal, the regulation should be fine (despite the shunt) and also the user is free to connect (or not) the negative terminal (or the positive terminal) to earth/chassis ground without affecting circuit operation. Sean --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .