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Regulating capacitors, vibration

Discussion in 'Electronic Basics' started by David Harper, Nov 11, 2004.

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  1. David Harper

    David Harper Guest

    Are there any advantages different types of capacitors have over other
    types for regulating voltage? In my specific application, I have 2
    ADCs, an accelerometer, and a pressure sensor (all of which use +5 as
    reference).

    As a follow up, does vibration affect capacitor's ability to regulate
    voltage? (i.e. does microstrain in the cap cause voltage
    fluxuations?) Are some more immune to vibration than others?

    Thanks in advance for any insight!
    Dave
     
  2. High-K ceramics (Z5U, Y5V) definitely exhibit microphonic properties.
     
  3. Tim Wescott

    Tim Wescott Guest

    -- and Tantalums, if you can use them, don't. I've been present when a
    problem was discovered in a pixel clock PLL that turned out to be
    microphonic caps -- the solution was back-to-back tantalums.

    Unless your application is very sensitive to power supply noise (which
    your accelerometer may be, if it's a strain-gauge type), you can
    probably decouple the power supply with such caps. Its really your call.
     
  4. David Harper

    David Harper Guest

    What about standard aluminum electrolytic caps? I'm just worried that
    vibration during flight may cause the accelerometer (and ADC's) to
    give inaccurate readings due to reference voltage fluxuations.

    Thanks again,
    Dave
     
  5. Tim Wescott

    Tim Wescott Guest

    I don't know, but I suspect they'd be OK. We used tantalums because of
    the allure of the solid sintered slug, and because aluminums dry out
    over 50000 feet. But aluminums have the same basic structure (really
    thin oxide dielectric formed by electrolytic action) so the ought to
    work -- try it, and use at your own risk.
     
  6. Rich Grise

    Rich Grise Guest

    Just put "mil spec" or variations in your search string. Mil spec
    parts, while being ten times as expensive a normal parts, are, in
    fact, characterized to operate over an astonishingly large range
    of hostile conditions, microphonics being one of them. A good, solid
    mechanical mounting is your best insurance against microphonics.

    And, notwithstanding I've been kind of out of the loop, and so
    haven't kept up with advances in technology, the term "silvered
    mica" keeps popping up in my alleged mind. Something about being
    paragons of stability, or maybe it was low HF ESR.

    (and, BTW, capacitors don't actually "regulate" voltage - a closer
    description would be "smooth out" the voltage, since they're sort
    of a charge storage reservoir. One instructor in tech school said,
    "A capacitor opposes a change in voltage; an inductor opposes a
    change in current.")

    Hope This Helps!
    Rich
     
  7. John Fields

    John Fields Guest

     
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