To choose a capicitor for active filter

Discussion in 'General Electronics Chat' started by Crowbar, Dec 28, 2006.

  1. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    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?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    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.
     
  3. Distort10n

    Active Member

    Dec 25, 2006
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    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.
     
  4. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    The system is working with frequencies from dc to 1KHz and with a voltage ranges 30mkV-2V
     
  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    10mkf and 30mkV (?!)

    Weird units, at least to me...

    What do they mean? NEVER seen them.
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
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    Interpreting this literally:

    10mkf = 10f

    30mkV = 30V

    Some clarity is needed.

    Dave
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    mkF means usually microfarads (mikrofarads) or uF.
     
  8. Dave

    Retired Moderator

    Nov 17, 2003
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    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
     
  9. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    I'm Russian that's why I have posted mkF istead of uF :)
     
  10. wireaddict

    Senior Member

    Nov 1, 2006
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    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.
     
  11. Distort10n

    Active Member

    Dec 25, 2006
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    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.
     
  12. wireaddict

    Senior Member

    Nov 1, 2006
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    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.
     
  13. lenin

    New Member

    Jan 2, 2007
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    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.
     
  14. wireaddict

    Senior Member

    Nov 1, 2006
    133
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    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.
     
  15. Murod

    Active Member

    Dec 24, 2005
    30
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    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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