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Capacitor advice

Discussion in 'Electronic Basics' started by beatbox, May 1, 2007.

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  1. beatbox

    beatbox Guest

  2. Metal film means that the capacitor is made of metal and
    plastic film. It is not very specific. Metalized film
    means that the metal is vacuum deposited on the plastic film
    and is very thin and compact, but may have fairly high
    series resistance. Foil film capacitors are made with
    layers of metal foil and film, stacked or wound around each
    other. Since the foil is generally many times thicker than
    the few atoms thickness in the metalized types, they have
    lower series resistance and handle large peak currents better.

    Then you have to ask about the kind of plastic the film is
    made of. There are many choices and each has some
    advantage. Cost, size, loss, temperature range, distortion
    are some possibilities.

    If the film type is not specified, the most common,
    polyester (mylar) is probably good enough and small and cheap.

    I might give more helpful advice if I knew the application.
  3. Phil Allison

    Phil Allison Guest


    ** Its a misprint.

    Should be " metallised film ".

    ....... Phil
  4. Eeyore

    Eeyore Guest

    It *could* be metal fim. Rare I know.

    More information is required.

  5. Phil Allison

    Phil Allison Guest

  6. beatbox

    beatbox Guest

    Thanks all for the helpful info. Here is the circuit, for
    clarification. It's a Midi -> CV converter. There are a few 100nF
    capacitors in there.
  7. Phil Allison

    Phil Allison Guest

    "Daniel Mandic"

    ** Hey look - some hairy critter just poked its shit ugly head up out of a
    dunny and puked !!

    ** Yeah - it.

    ROTFL !!

    ....... Phil
  8. Eeyore

    Eeyore Guest

    Polyester / mylar film types will be just fine there. Very commonplace and very
    inexpensive. Not special at all.

  9. The capacitors you list would work for this application,
    which is not at all critical. They are called supply bypass
    capacitors, that provide a small local charge storage where
    quick pulses of current may be needed without those pulses
    having to race through the inductance of the supply
    distribution lines.

    More important is exactly where on the circuit board they
    are mounted. They need to be connected between power supply
    lines and ground, not in a cluster as shown, but at the
    points where these supply lines connect to certain chips
    being powered. For the +-15 volt lines, that would be right
    at U6 and U8, and for the +5 line, right at U7.

    It wouldn't hurt at all to add a pair between the +5 and +15
    volt lines to ground at chips U3 and U4, too.

    However, the voltage regulator, U2, may not be stable unless
    C3 and C4 are very close to it.

    If this project includes a printed circuit board, then these
    locations are already taken care of, and all you have to do
    is check that the capacitors you order have lead wire
    spacings that fit the hole spacing of the board.
  10. beatbox

    beatbox Guest

    It does have a PCB. Thanks again!
  11. John Fields

    John Fields Guest

    Hardly. Every ceramic capacitor in the world is a metal film
    capacitor, which type would be fine in the OP's application.

    If the author of the schematic meant metalized film, then the error
    was in not designating the caps "metalized film" or hyphenating
    "metal film."
  12. Phil Allison

    Phil Allison Guest

    "John Fields"

    ** Dear John ....

    The actual issue here is the industry accepted, unambiguous identifying type
    name - as required for ordering purposes.

    Try to follow the context.

    Even when it is implied rather than visible.

    ...... Phil

  13. There are also metalized glass capacitors, if your budget is big
    enough, along with metalized Mica. One 25 KW UHF transmitter I worked
    on used some very large open metalized mica capacitors that cost over
    $900 in the '80s. It was at the output of the 250 watt driver stage.

    Shove that up your #$%^&* UK donkey! ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  14. John Fields

    John Fields Guest

    Dear Phil,

    In the context that they're being used as supply bypass capacitors,
    I believe it's much more likely that they're ceramic than metalized
    plastic film, so the term 'metal film' is probably referring to the
    sub-micron thick metal film "plates" sandwiched in between the
    ceramic dielectric. An unusual usage for 'metal film', but stranger
    things have happened, wouldn't you agree? :)
  15. Whose hair?
    Has it done good, yes? :) You rolled over my puke-dot.

    But I got somehow in the right thread :). Interesting.... Allthough, I
    would suggest a real VC Analogue Sequencer. MIDI to CV are rightly
    wrong, IMO.

    Best Regards,

    Daniel Mandic
  16. Eeyore

    Eeyore Guest

    I was referring to *film and foil* types as opposed to metallised film. They are
    obviously noy needed here. I agree with your comment about the author of the
    schematic btw.

  17. Eeyore

    Eeyore Guest

    Polyester film caps are widely used in European designed products for decoupling
    actually. I gave up on ceramics after encountering a high failure rate when using
    them (50V rating) on 17V supplies for decoupling.

  18. Phil Allison

    Phil Allison Guest

    "John Fields"
    "Phil Allison"

    ** That is NOT the context.

    YOU cannot invent context.

    ......... Phil
  19. John Fields

    John Fields Guest

    Yeah, that's kinda scary, especially when polyester caps are

    What was it with the ceramics, a bad batch of caps or a really spiky
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