On Wed, Apr 20, 2011 at 4:55 PM, V G wrote: > On Wed, Apr 20, 2011 at 4:26 PM, Oli Glaser wrot= e: > >> The 2N2222 probably came from the circuit I posted. It was just meant t= o >> serve (with the 2N3055) as a reasonable approximation of a darlington. I >> was expecting VG to replace it with an appropriate TO-220 (or similar) >> when actually making the circuit. >> >> > I actually thought that a 2N2222 would be okay, but I'll replace it with = a > TIP41 (that was my other option anyway). I forgot about total power > dissipation of that transistor. > > If I connect the control transistor's collector to 5V instead of the > "battery", doesn't that defeat the purpose of the Darlington? Wouldn't th= at > add in inaccuracies again since the extra current is coming from 5V inste= ad > of the "battery" and the measured current strays farther from the > "battery's" current? > Just measured the base current of the 2N3055 and it seems to be going as high as about 500mA, so the current measurement would be off by 500mA. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .