To choose a capicitor for active filter

Thread Starter

Crowbar

Joined Dec 19, 2006
32
I need 10mkf capicitor for a HPF(it will be a part of portable magnetometer). Better to use polypropylene but 10mkF polyprop. cap. is bulky- what about tantalum or ceramic?
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

Tantalum is polar and has wierd characteristics when exposed to AC. They tend to short, for instance. Ceramic is hard to use. The specs are usually the value +80% to - 20%. Not too accurate, which is critical for filtering. And they tend to be microphonic, and contribute noise when shaken or vibrated.

You have to choose components based on application and not necessarily on size.
 

Distort10n

Joined Dec 25, 2006
429
I would go with the ceramic or silver-mica. I would not worry about noise contributed by microphonics unless your application is going to be subjected to shocks/vibrations as part of the application itself. Ceramics are typically used in high speed applications; e.g., DSP's.
 

Dave

Joined Nov 17, 2003
6,970
mkF means usually microfarads (mikrofarads) or uF.
As a terminology this is very confusing, I could understand mcF, but mkF implies milli-kilo-Farad which (interpreted literally) means Farad. Thankfully I haven't come across this terminology before.

Thanks for the clarification anyway.

Dave
 

wireaddict

Joined Nov 1, 2006
133
If you're using a 10uF cap, electrolytics are the only ones that large [at least, that I know of, that are commonly available]. Also, the cap needs to be a non-polarized type since it will have AC applied to it.
 

Distort10n

Joined Dec 25, 2006
429
If you're using a 10uF cap, electrolytics are the only ones that large [at least, that I know of, that are commonly available]. Also, the cap needs to be a non-polarized type since it will have AC applied to it.
That is not necessarily true. As long as both sides of the cap are DC biased then AC squiggles are ok. You see this in video apps with TV's from time to time.
 

wireaddict

Joined Nov 1, 2006
133
Yes, a DC/polarized electrolytic will work fine provided the AC voltage never exceeds the DC in the wrong direction; however Crowbar never said that there would be DC with superimposed AC on this cap. Not knowing the voltage on this cap I suggested using a N/P type. Regards.
 

lenin

Joined Jan 2, 2007
1
go with the ceramic or silver-mica. I would not worry about noise contributed by microphonics unless your application is going to be subjected to shocks/vibrations as part of the application itself. Ceramics are typically used in high speed applications; e.g., DSP's.
 

wireaddict

Joined Nov 1, 2006
133
But does the capacitance of ceramic or silver mica caps go that high [10uF] [and at a reasonable price]? If so, I agree, either would be a better choice than electrolytics here.
 

Murod

Joined Dec 24, 2005
30
When applied to AC voltage with unknown bias, two back-to-back series electrolytic capacitors can be a cheap solution.

Hasan Murod.
 
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