[sdiy] LEDs again

Rutger Vlek rutgervlek at gmail.com
Thu Jun 25 16:39:47 CEST 2015


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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