On 20/04/2011 02:04, V G wrote:
> Hey all,
>
> I made a constant current source (for battery drain testing, charging,
> pretty much any application). But there's so many variables that I don't
> know how to calculate for it. So many of the components influence the
> current through Q1 (power BJT) that I don't know how to select the values
> and which one to vary to get the widest current selection range.
>
> Circuit attached.
>
> For the circuit above, I guessed the values and selected about a 1A curre=
nt
> source.

Not got much time right now to advise on the circuit, but a couple of=20
things - you may get strange results if you don't select a proper=20
transistor (it will use the default) so right click and pick a suitable one=
..
Also you can use m for milli, u, n, p, f and Meg for Mega. For supplies=20
you can use the net labels so you only have to have say one 5V supply.
I would probably just try driving the base of the darlington directly=20
with the output of the opamp. The current through the transistor will be=20
whatever is necessary for the opamp to stabilise itself (i.e create the=20
correct voltage across the sense resistor) this is maybe the easiest way=20
to think about it.

--=20
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