V G wrote:
> If I connect the control transistor's collector to 5V instead of the
> "battery", doesn't that defeat the purpose of the Darlington?

Yes, it would in the sense of current accuracy.  It's a tradeoff whether yo=
u
want to go to a lower voltage or have better current accuracy.  You
orignally said this was only for testing a battery, so the extra voltage
drop of a darlington wasn't a issue.

Another possibility is to put a N channel FET in place of the small
transistor that drives the power transistor.  That will gain you maybe
around 200mV since the voltage drop on the FET would nearly 0.

Personally I don't see why you need such a low compliance voltage for
testing of a 3.6V battery.  I would stick with the darlington configuration=
,
which should work down to maybe around 900mV.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.