On Tue, Apr 19, 2011 at 10:06 PM, V G wrote: > On Tue, Apr 19, 2011 at 9:44 PM, Oli Glaser wrot= e: > >> 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 *negativ= e* > 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 Darling= ton > pair, wouldn't the be a *positive* feedback control? > > ----- Or should I do active control with a microcontroller? I can have the microcontroller read the output of the opamp and control the Darlington pai= r through a DAC. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .