High frequency capacitors

Discussion in 'General Electronics Chat' started by TAKYMOUNIR, Nov 14, 2012.

  1. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
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    What is the difference between the high frquency cap and other cap (i know from its name that it is better in hf) is this work like other cap block dc and pass ac or what is the difference and which caps is the best in hf
    and what will happen if i use regular cap istead of using hf cap
    thanks
     
  2. takao21203

    Distinguished Member

    Apr 28, 2012
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    Standard caps just don't work right with H.F.

    Sometimes you will just experience some loss.
    Sometimes the cap will get hot.
    Sometimes the circuit may not work properly or not at all.
     
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  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    They are typically optimized for low series inductance and low equivalent series resistance at high frequency.
     
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  4. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
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    which kind of capacitors is good in high frequency and high voltage ,and high frequency and low voltage
    thanks
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I hate to say this, but Google "high frequency capacitors". Manufacturers want you to buy their parts, so they will tell you all about them.
     
  6. takao21203

    Distinguished Member

    Apr 28, 2012
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    That's really too much generic.

    Sometimes regular caps also work, but you'd trade off efficiency. And you'd obtain more noise. There is really the case when this does not really matter.

    Even a long cable is a capacitor already. If you apply high frequency, you'd experience capacitive resistance. The higher the frequency, the lower that resistance will be.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    How is this relevant to the OP's question? BTW, capacitors have reactance. Any resistance is usually undesirable, especially in high frequency applications.
     
  8. takao21203

    Distinguished Member

    Apr 28, 2012
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    Capacitors also can opposse currents due to their internal inductance.
    So it can appear like their internal resistance is increased.

    Relevant answer? What does OP mean with high voltage?

    10V could be seen as very high.
    Or 200V. Or 10 kV.
     
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  9. JMac3108

    Active Member

    Aug 16, 2010
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    A real capacitor has inductance in addition to capacitance. A large part of this is in the packaging of the cap. At a high enough frequency the cap will start becoming less capacitive and more inductive.

    Smaller packages have less inductance, i.e a surface mount ceramic cap is better than a through hole ceramic cap. An 0402 surface mount is better than an 0603, etc...
     
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  10. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
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    high voltage mean kv like 5kv or 10kv or more
    thanks
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have used styroflex capacitors (polystyrene) in some RF oscillator circuits for their stability.
    This page of the cap site has more info on them:
    http://my.execpc.com/~endlr/film.html
    (scroll a bit down).

    Bertus
     
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