On Thu, Apr 14, 2011 at 4:32 PM, Olin Lathrop wr= ote: > A bipolar would work "better" as a controlled current sink since that's > what > it does naturally. However, if absolute current accuracy is important, > then > the FET is better. With a bipolar, the current sensed by a low side sens= e > resistor will be off from the battery current by the base current. This > error goes down with gain, so with a high enough gain it doesn't matter. > If > you have the voltage headroom, you can use a darlington to effectively > increase gain to the point where the error is immaterial for ordinary > battery testing. That's a good idea. Thanks. I'm looking to make a current source which will typically test batteries at around a 500mA - 2A drain. What gain values should I be looking at when selecting a BJT? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .