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which capacitor is best

Discussion in 'General Electronics Discussion' started by grahamdavidmoore, Jun 23, 2014.

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  1. grahamdavidmoore

    grahamdavidmoore

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    Jun 23, 2014
    hi, I've just built a circuit from the internet which calls for a "C0G/NP0 or a mica for better stability", I have some polystyrene and some polycarbonate and some metalised film, which ones would be better? many thanks.
     
  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Can you post a circuit diagram and point to where the capacitors are on it. Gives up a better idea and we can then answer you accurately.
    Thanks
    Adam
     
    KrisBlueNZ likes this.
  3. grahamdavidmoore

    grahamdavidmoore

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    Jun 23, 2014
    Hi, its c4 on the diagram
     

    Attached Files:

  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Polystyrene and polycarbonate capacitors are film capacitors, too.

    Here's an overview of the losses of different capacitor materials. Polycarbonate and polyester have higher losses than C0G, polypropylene and polystyrene have considerably lower losses than C0G.

    The tempco of all of these film capacitor materials is worse than that for C0G.
     
  5. grahamdavidmoore

    grahamdavidmoore

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    Jun 23, 2014
    Thanks for your reply, so is the polystyrene one the best choice that I have?
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    If you don't want to buy a C0G, yes.
     
  7. grahamdavidmoore

    grahamdavidmoore

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    Jun 23, 2014
    I'll get one when I next order, I can see what difference it makes, just wanted to use the best I had at the moment, many thanks for your help
     
  8. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Looks like it a timing capacitor for some kind of linear ramp. Probably the best all rounder for the price is going to be a negative positive zero (NP0). Good all round over temperature and capacitance doesn't change much with applied voltage. But tolerance is generally +/-5%. Polystyrene is another good choice but can be damaged by soldering if your not careful.
    Adam
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That's a nice little circuit. A VCO for a synth, right?

    If the designer recommends a C0G/NP0 that's what you should use. This one from Digikey looks good: http://www.digikey.com/product-detail/en/C412C222J5G5TA7200/399-4487-1-ND/818344

    The initial tolerance is only ±5% but that can be compensated by adjustment. The temperature coefficient is what's important. AVX claim better than 30 ppm/°C for their C0G units and that's probably the best you'll find unless you want to spend big bucks.
     
  10. grahamdavidmoore

    grahamdavidmoore

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    Jun 23, 2014
    Yes it is a vco so the stability is the main thing and vco's have always been very susceptible to temperature change
     
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