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Electronics => Electronics => Topic started by: LunchBox! on April 30, 2009, 10:29:54 PM

Title: noise filtering caps
Post by: LunchBox! on April 30, 2009, 10:29:54 PM

Is there a any downsides to using larger capacitors than ~.1uf
like 10uf or 100uf?

Title: Re: noise filtering caps
Post by: aludra_55 on April 30, 2009, 10:45:23 PM

i'm a newbie...  i guess capacitor is like a glass that you could fill in with water...
the bigger the glass, the more time it takes to fill it...  and vice versa with smaller
glass...  same thing with discharging it...  it is faster to empty a small glass of water
by sipping it through a straw than a huge glass of water...

so you have to ask yourself, what are you using the caps for?... are you using it
as a filter, decoupling, etc?...   if you're going to use it to just to further stabilize your
voltage for your microcontroller, then putting small caps like .1uF really close to your
uC would be good in catching those fast short spikes...  if you're just using it for
your voltage regulator, then 100uF for the input voltage going to the regulator and
10uF for output would be good...  but if you're using it as a low pass filter, then you
have to specifically choose your caps based on what frequency you want to filter...

but that's just me...  i'm still a newbie..   

Title: Re: noise filtering caps
Post by: Soeren on May 01, 2009, 07:26:37 PM

Hi,

Quote from: LunchBox! on April 30, 2009, 10:29:54 PM

Is there a any downsides to using larger capacitors than ~.1uf
like 10uf or 100uf?

If I asked you if there would be any downsides to using a larger knife for the next cut I have to make, then what would you answer (not knowing if I'm a surgeon, a butcher or perhaps was about to "skin" a whale).

That said, I have to say yes, as any choice of component values you make will be a compromise.
I have no idea of what you're trying to filter, but from the values mentioned, it could be a power supply of some sorts and then the 100nF (0.1µF) might be calculated for optimum performance and changing it for a 10 or 100 times larger value will mean a shift in what noise frequencies it will filter, as larger electrolytes are less efficient towards higher frequencies (and a higher ESR).
It is common use in supplies, to parallel connect 2 to 3 capacitors, eg. 4700µF//6.8µF//10nF, to get a wideband noise dampening.