On Mon, Mar 15, 2010 at 11:17 AM, Bob Blick <bobblick@ftml.net> wrote:
> Even if the negative rail is ground, this circuit is valid. It is not
> affecting the accuracy. There is no need for a "rail to rail" opamp in
> this circuit.
>
> I've used this opamp and the LM324(the quad version of the LM358) in
> this type of circuit for decades :)
>

Ok, just how low this current source can go down to? Say if I
drive the Vin+ with a 16bit DAC (0...1.25V), how good the
resolution of the current source can be? The input offset
and leakage current may play a part though.

We do not use LM324/LM358 but rather ADI OP2177
and sometimes we do need the negative rail to achieve
good near 0mA current depending on the accuracy requirement.

When the accuracy requirement is not as high, we
use Rail to Rail input OpAMP like OP213FS.

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