[sdiy] LEDs again

[blacet at blacet.com]

Low current or ultra bright LEDs will often work quite well at 1 or 2 mA.

The most important thing when designing the PCB is to have a separate
return trace for the LEDs to the board power input.


> Hi guys,
>
> As you may recall from a previous post of mine I've been working on LED
> indicators for some Eurorack modules and especially worried about keeping
> the power rails clean (e.g. using a constant current source and use a
> 'bypass' transistor to switch the LED).
>
> Now I'm looking at a much more simple setup. Just an op-amp buffer feeding
> it's output (through a 1K) into a led that's connected to ground. For my
> own sanity, I wanted to check what happens if keeping things as simple as
> possible. I was expecting to see the LED switching "on/off" in the current
> drawn from the power rails, in the order of the amount of current I feed
> through the LED (about 10mA). But I'm not seeing current jumps anywhere
> the magnitude of 10mA on the rails in Spice at all! Is there some way the
> opamps internal operation redirects current not being able to flow to the
> output, such that total current draw is maintained (not loading directly
> on the supply)?
>
>  Best,
>
> Rutger
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