[sdiy] LED driver circuit

[Neil Johnson]

David wrote wrote:
> The circuit is as follows (for the positive ones):
>
> Filter Output ---> 200k ---> NPN Base
>
> +15V ---> 49.9k ---> LED ---> NPN Collector
>
> NPN Emitter ---> Ground

Aside from the issue this circuit has (as addressed by Phil and Richie),
with only an op-amp and resistor you can get correct VCCS control of
a bipolar LED (red/green). A TL074 and four resistors will be less PCB
area than four transistors and 12 resistors.  Times 2 (as I believe the
Intellijel Octature has eight outputs) will be quite a saving in PCB area.

I know it's a bit more rework than you'd like, but with the additional 
functionality AND saving in PCB area I strongly suggest you to try it.

Cheers,
Neil
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