[sdiy] Op Amp LED driver / Current Source problem/solution

[Roman Sowa]

Does your DAC *really* go to 0V, or maybe, say 50mV or even higher? That 
forces about 1uA to flow thru LED and is enough to see delicate dimmed 
light in a LED. Your 1M resistor shifts threshold a bit higher, so DAC 
can drop below that, opamp goes way down to -10V or so and LED is off.
And to prevent the OPAMP from switching down to negative supply, add 
paralel diode in reverse with LED.

Roman

W dniu 2014-11-26 20:16, Justin Owen pisze:
> Just in case my original post wasn't clear...
>
> This config: http://www.sdiy.org/juz/unipolar_LED.png
>
> works just fine with the required input signal between 0 and +5V.
>
> My concern is a) I was wondering why the LED wouldn't dim completely without that 1M R and b) I've never seen that 1M R added to this config before so I'm worried I've fixed one problem at the risk of creating others (or just done something else dumb).
>
> Thanks,
>
> - Justin
>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>