On 20/04/2011 03:06, V G wrote:
>> >  I would probably just try driving the base of the darlington directly
>> >  with the output of the opamp. The current through the transistor will=
 be
>> >  whatever is necessary for the opamp to stabilise itself (i.e create t=
he
>> >  correct voltage across the sense resistor) this is maybe the easiest =
way
>> >  to think about it.
>> >
>> >
> I'm not understanding this. Right now, the opamp output drives a*negative=
*
> feedback control. The higher the opamp output, the lower the input to the
> Darlington pair. If I connect the opamp output to the base of the Darling=
ton
> pair, wouldn't the be a*positive*  feedback control?

Yes, sorry - I didn't check closely, but I wasn't being too literal. You=20
would need to change it as required, so you could drive the darlington=20
with the opamp output and connect the top of the sense resistor to the=20
inverting input.
Then control the current with a pot on the non-inverting input.


--=20
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