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Ceramic capacitors

Discussion in 'Electronic Design' started by E, Sep 14, 2009.

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  1. E

    E Guest

    Just made oscillator from 74HC14, 1k resistor and Taiyo Yuden Y5V 10uF
    capacitor.
    Results:
    Capacitor other end biased to 2V => 126 Hz out
    At 36 V bias 2470 Hz out
    That means 1:19 change in capacitance!
    Maybe I can build some low frequency VCO out of these...
    Amazing things.

    -ek
     
  2. Joerg

    Joerg Guest

    Shhhhht! Don't let out all the secret tricks :)
     
  3. E

    E Guest

    Did you verify that the 2V and 36V supplies were effective shorts to
    There were one film cap + 100u electrolytic to ground + whatever is in lab
    supply
     
  4. Joerg

    Joerg Guest

    Yup:

    http://www.avx.com/docs/Catalogs/class2-gp.pdf

    Many younger engineers consider Y5V and Z5U junk. Little do they know ...
     
  5. Joerg

    Joerg Guest

    Yes, check out these:
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=478-4238-ND

    Datasheet:
    http://www.avx.com/docs/Catalogs/class2-gp.pdf

    But they only come in through-hole.
     
  6. Klaus Bahner

    Klaus Bahner Guest

    Well, I'm not a young engineer any longer and tend to consider Y5V and
    Z5U as junk.
    I don't even regard this as "secret trick". Sure you can build a VCO
    this way, but then you also have to add a thermostat, which will turn
    the secret trick into an expensive trick. Not to mention that the
    thermostat won't cure the thermal hysteresis problem.

    Klaus
     
  7. Joerg

    Joerg Guest

    It's the same with varicaps, FETs and whatever else you want to use in
    this function. A good designer designs out those dependencies or makes
    the circuitry live with them :))

    It is not trivial to build a variable resonant circuit in the kHz range
    where the varying element is supposed to cost no more than five cents,
    other than with Z5U and such. I've also done super-cheap spectrum
    spreaders that way for EMI mitigation. There, a temperature-dependency
    doesn't matter at all.

    Of course, in Phil's case he needs to watch out where he puts the
    capacitor. It should not be in a path where there would be large signal
    amplitudes across it, else the whole thing will become uncomfortably
    non-linear.
     
  8. Joerg

    Joerg Guest

    Then just take a look at Z5U and Y5V for some other cap. They won't be
    grossly different but AVX doesn't have the curves in the HV cap
    datasheets. This would give you a first estimate of how bad it would be
    at 50mV. Should be pretty miniscule.
     
  9. Joerg

    Joerg Guest

    P.S.: Digikey carries over two million of this Y5V capacitor in stock,
    0.253 cents/piece (US) if you buy 50000:

    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PCC1731TR-ND

    That many engineers can't be wrong :)
     
  10. John Larkin

    John Larkin Guest

    Think parametric amplifier!

    I've seen kilovolt shock lines that use ceramic caps as the nonlinear
    elements.

    John
     
  11. JosephKK

    JosephKK Guest

    Some 30 years ago i was testing low tempco chip caps that had a huge
    voltage coefficient. I wish i could remember what they were made of.
     
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