[sdiy] How to Determine Value of Power Supply Decoupling Caps?

[harrybissell]

Hi Scott.

Yes, yes, yes, yes, and... no

You DO use current draw (which would make the voltage drop at the cap or
allow more ripple to be seen....

What the module is doing is very important.  Just lighting some LEDs is going to

be a lot different than a high quality preamp or VCO...

Educated Guess... hell yes. How big can you stand it ???  And if you did make it

that big... how long would it take to charge, or could your supply even GET
there.
(like .1uF is too small and 10,000uF might be too large...

What frequencies are you trying to decouple... Getting rid of ripple takes big
uF...
getting rid of RF takes small.  The smart bet is to parallel a large lytic with
a good
small ceramic cap.

Yes.. all of the above

No... not "none of the above"

H^) harry

Scott Stites wrote:

> Hi List,
>
> This is something I've been wondering about for a while.  I know that one
> should use caps with twice the voltage rating that one would expect the caps
> to bear, but what criteria do you use to determine the capacitance value of
> the caps for filtering on power entry of a module?
>
> Do you base it on the amount of current the module draws, what the module is
> doing, an educated guess, all of the above or none of the above?
>
> Any guidance most welcome,
>
> Thanks,
> Scott