[sdiy] filter cap needed?

[Colin Hinz]

On Thu, 26 Mar 2009, Simon Brouwer wrote:

> Colin Hinz schreef:
>> On Wed, 25 Mar 2009, db wrote:
>> 
>>> I guess I've now been convinced to do it. :)
>>> 
>>> Am I correct in that it just needs a .1uf  from 5v to gnd?
>> 
>> That should do it. Close to the regulator pins too, naturally enough.
>
> Actually it doesn't matter if it is far from the regulator.

OH YES IT DOES!

Otherwise, it wouldn't be necessary to specifiy it at all, in most
cases, because IC decoupling would take care of it.

> The capacitor on the *input* of the 78xx must be close to it, though.

Bypass caps in general must be close to whatever they're stabilising,
because otherwise you're just building itty bitty L-C tank circuits.

And if your output L-C is resonant with load transients, you can get the
4V p-p "regulator" oscillator I mentioned earlier.

- Colin