On 2013-02-06 6:16 PM, Sergey Dryga wrote: > Mark Rages gmail.com> writes: >=20 >> You are measuring current upstream from the output transistors, so if >> you go BJT you will have error introduced by the base current, which >> will be added to the output current. The resultant error may be >> acceptable with Darlington outputs. >> > Would not the base current sourced by Vsupply, and, therefore not measure= d in > the collector current? This assumes that output transistor will be npn The base current would be sourced by Vsupply, but the opamp supplying the current would be connected directly to Vsupply, not through the resistor. But since the power Darlingtons I would use have a pretty uniform DC current gain of 1000, I don't mind a 0.1% error in current, especially at high current. Not a big deal. I'll probably stick with the MOSFETs to begin with anyway. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .