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

[Justin Owen]

Hello,

I've previously used this: http://www.sdiy.org/juz/bipolar_LED.png as a bipolar LED driver where each LED shows either the positive or negative-going portion of a signal.

Have a need for a nice linear driver for a varying signal e.g. sine wave LFO going between 0 and +5V and assumed I could use the same circuit and just remove the bottom, negative LED.

That version doesn't turn the LED fully off when the input signal gets to 0V...

...but adding a big old 1M R to the supply rail fixes that:

http://www.sdiy.org/juz/unipolar_LED.png

Is that a valid fix or is this potentially going to cause problems elsewhere in the curcuit/make bad things happen?

Thanks.

- Justin