On Tue, Apr 19, 2011 at 9:44 PM, Oli Glaser wrote= : > Not got much time right now to advise on the circuit, but a couple of > things - you may get strange results if you don't select a proper > transistor (it will use the default) so right click and pick a suitable > one. > Too right, you. > Also you can use m for milli, u, n, p, f and Meg for Mega. For supplies > you can use the net labels so you only have to have say one 5V supply. > Will do, boss. > I would probably just try driving the base of the darlington directly > with the output of the opamp. The current through the transistor will be > whatever is necessary for the opamp to stabilise itself (i.e create the > correct voltage across the sense resistor) this is maybe the easiest way > to think about it. > > I'm not understanding this. Right now, the opamp output drives a *negative* feedback control. The higher the opamp output, the lower the input to the Darlington pair. If I connect the opamp output to the base of the Darlingto= n pair, wouldn't the be a *positive* feedback control? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .