On Fri, Apr 15, 2011 at 9:56 AM, Olin Lathrop wr= ote: > That depends on how much error you can tolerate. You can probably get > transistors with a gain of 30 in that range, especially since you don't > need > high collector voltage ability. If one part in 30 is good enough, then > that's fine. If not, you can use a smaller transistor around the big one > to > make a darlington, which then will have a combined gain that is the produ= ct > of the two individual gains. If the second transistor has a gain of at > least 50 (easy to get), then the darlington gain would be 1500. > > You could also use a FET between collector and base to drive a big fat TO= -3 > power transistor, like the ancient but brick-outhouse 2N3055. That > channels > the base current to where it becomes part of the overall current, so ther= e > is not error, and a gain as low as 10 or 15 from the big transistor is > fine. > I'm not understanding where the error comes from, or what exactly the error is. Also, I'm not sure if I need put some sort of a resistive load on the BJT, or if I can just connect it to ground. Why would I have an error if I can control the BJT by sensing the current through a current sense resistor? (something like the top few here: http://dipmicro.com/store/index.php?act=3DviewCat&catId=3D529) I'm going to make some simple circuits on LTSice and try them out. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .