[sdiy] dare I say - decoupling?

[JH.]

> > Would it be ok in the feedback loop of an op-amp like in some of the old
> > Oakley stuff?
>
> Doesn't help. The point of Jürgens arrangement is that you locally consume
as
> much current at any time, regardless of the LED (or LAMP) being on or off.
> By doing that, there is a much lower shift in current which needs
decoupling.
> The benefit is that the same DC current is pulled and there is almost none
> shift which needs to be decoupled.
>
> Just tossing it into the feedback loop of an op-amp will not help to
acheive
> the constant DC-pulling.

Magnus is right.

But this configuration can give us an example for something else:

Asuming the opamp with the LED in its feedback loop (opamp 2) is used in
inverting
configuration (+inp tied to GND, input resistor connected to -inp
acting as virtual GND), driven by another opamp (opamp 1).

Then all the AC current from LED driving is running thru the positive and
negative supply,
leaving the GND completely undisturbed.

And then you want your bypass capacitors from opamp 1's positive supply pin
to
opamp 2' negative supply pin, and possibly a second cap the other way round.

(Not talking about the caps you need for stability - just talking about the
caps to
keep AC load currents local.)

JH.