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¿What is the difference among capacitors?

Discussion in 'Electronic Basics' started by chriswilliams, Dec 20, 2005.

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  1. As it is known there are different types of capacitors:
    *Electrolyitic
    *Tantalum
    *Ceramic

    But ¿which is the difference among them.?

    It wanted to know if they can be substituted among them,
    that is to say if I can substitute one ceramic by
    one electrolytic or an electrolytic for one of tantalum.

    Thanks in advance for any comment.
     
  2. Andrew Holme

    Andrew Holme Guest

    Capacitance value for one thing. Ceramics cover from 1pF up to just short
    of 1uF. Then, there's some overlap as electrolytics and tants take over for
    larger values. Tants tend to be physically smaller than electrolytics for
    the same capacitance / voltage rating. For really large values,
    electrolytics are your only choice.

    Another difference: ceramics are not polarity sensitive.

    Those three are not the only types: there's polystyrene, polyester layer,
    monolithic ceramic .... each offering different performance in terms of
    precision, temperature stability, physical size, voltage rating,
    self-resonant frequency ....
    If the capacitance and rated voltage match, it may be possible to substitute
    an electrolytic for a tant, or vice-versa.
     
  3. Here is a good place to start:
    http://my.execpc.com/~endlr/index.html
     
  4. Guest

    I saw those 6w FL dc driver circuit was useing tantalum cap instead of
    cheap ceramic cap, reason was unknow, may be due to the driver's
    frequency and ceramic can't handle such high frequency ?
     
  5. PeteS

    PeteS Guest

    Minor nit - I use 100uF ceramics (Panasonic). Not suitable at anything
    approaching a high voltage, but great below 5V.

    Whether devices can be substituted depends where it is used. All caps
    have other specifications, such as ESR (equivalent series resistance),
    ESL (Equivalent series inductance), leakage, ripple performance, surge
    performance, rms current handling and a host of other variations due to
    environmental conditions as well as the ones listed by Andrew.

    In feedback loops esr, in particular, becomes a critical issue. See for
    instance, the datasheet linked here:
    http://www.national.com/pf/LP/LP3961.html

    In the application hints, you'll find the output esr and input C - esr
    are considered (and important for loop stability).

    The other characteristics of the various types of cap can become issues
    in other circuits.

    Another quick example: tantalums have relatively poor surge performance
    (they can become spectacularly pyrotechnic), so choosing one where such
    a surge may exist is not as simple as looking at rms handling and
    capacitance.

    So the answer is not a simple yes or no - as always in engineering 'It
    Depends'

    Cheers

    PeteS
     
  6. PeteS

    PeteS Guest


    There are more than that

    A few that come to mind:

    Polystyrene
    Mica
    Mylar
    Air (used to see them in old radio sets)
    Oil (really! I've used them)
    Polyester
    Polyphenylene sulphide
    Polypropylene
    Niobium Oxide
    Polymer tantalum (a variation on a theme)
    Then there are things like the Sanyo TPA POSCAP (Solid electrolytic,
    sintered tantalum anode, Polymerised organic semiconductor electrolyte)

    Ceramics themselves have some variety
    Disc and plate
    Multilayer
    (I am sure the crowd will join in and add things I have forgotten to
    add or simply not come across)

    Each has their pros and cons - Mylar for instance, has superb
    dielectric characteristics across temperature amongst other things.

    Cheers

    PeteS
     
  7. Jasen Betts

    Jasen Betts Guest


    ceramic: low incuctance, low resistance, suited to radio frequency work.
    tantalum low-ish resistance, compact, high-ish capacity
    electrolytic, moderate resistance, large capacity, cheap.

    for filtering often a ceramic is paired with a tantalum or electrolytic.
    the ceramin deals with the sharp spikes and the other one absorbes the
    blunter surges.
     
  8. Jasen Betts

    Jasen Betts Guest

    waxed paper often used alongside air and mica caps. (obsolete)

    glass (leyden jars used in some home-made tesla coils
    and the back half of a CRT)

    I've also seen some with bitumin (I think) in them used for powerfactor
    correction (PFC) in some old fluorescent lights.



    Bye.
    Jasen
     
  9. Mebe. But mylars have huge amounts of parasitic inductance, making
    them pretty hopeless for RF applications. As someone else said, the
    choice of capacitor type is governed by the intended application.
     
  10. Good point. This often confuses a lot of folks. They see a 100nF in
    parallel with a 4.7u and can't understand why the design doesn't
    simply specify one capacitor of equivalent value. This example
    illustrates that cap choice often goes way beyond just the desired
    value.
     
  11. Deefoo

    Deefoo Guest

    Because 4.8u caps are hard to find ;)

    --DF
     
  12. Jamie

    Jamie Guest

    your joking rite?
     
  13. PeteS

    PeteS Guest

    I have designs that are 100% ceramic, as far as the caps go (Not all
    designs, but there are times it can work). Makes the power supply loop
    a little difficult to compensate, but definitely worth the effort. Even
    so, I agree on the confusion - and I still bypass my 100uF ceramics
    with a 0.1/0.01uF on occasion. Most cap mfrs now now give Z vs. F
    curves for each cap (although you may need to dig that out of their web
    sites) which can make life somewhat easier.

    Artificial intelligence is no match for natural stupidity

    Cheers

    PeteS
     
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