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

Tim Ressel timr at circuitabbey.com
Wed Nov 26 17:55:45 CET 2014

Have you tried replacing the LED with a diode?

Tim Ressel
Circuit Abbey
timr at circuitabbey.com

From: Justin Owen <juzowen at gmail.com>
To: SDIY List <Synth-diy at synth-diy.org> 
Sent: Wednesday, November 26, 2014 8:06 AM
Subject: [sdiy] Op Amp LED driver / Current Source problem/solution


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:


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


- Justin

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