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regulator capacitor voltage value

Discussion in 'General Electronics Discussion' started by qweets, Nov 18, 2012.

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  1. qweets

    qweets

    48
    0
    Sep 26, 2010
    hello

    i have a 12v regulator and a 5v regulator that i need to add caps too.

    in my parts box i have a fair few

    1000uf 63v caps (more of)
    1000uf 35v
    470uf caps 35v
    ( i will use smaller ceramic also .1uf .33uf.)

    the circuit may pull aprrox 1.5amps fromt the 12v regulator.

    But i wonder does it really matter if i use 63v or 35v or 1000uf or 470uf?
    i rememer reading somewhere that bigger is better on a regulator.

    thanks for help : )
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    Are these capacitors on the input or output side of the regulators?

    If on the input side, then a large capacitor may be a good thing if you're rectifying AC. In that case somewhere between 1500 and 2000 uF would be a typical figure for a current in the range you're suggesting.

    The capacitor voltage needs to exceed the voltage applied to it, the 35V capacitor would be fine for voltages up to 25V or so, and the 63V caps for voltages up to perhaps 50V.

    If they're output caps then you probably don't need more than 470uF, and if you're adding a capacitor of this size you may want to consider a reverse biased diode across the regulator to prevent the capacitor from discharging through the regulator.
     
  3. qweets

    qweets

    48
    0
    Sep 26, 2010
    thank you very much steve

    they are for the input side of the regulators.

    I shall buy some 2000ufs just to be on the safe side.
    and shall do a google on the diode across the regulator idea.

    thanks : )
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    You can just put capacitors in parallel to sum their value. So two of your 1000 uF capacitors in parallel is 2000 uF.

    That's why I mentioned 1500 to 2000 specifically, since you can make up those values easily (1470 is close enough to 1500). The decision as to how you make it up is yours. You can even go higher if you wish, but there are diminishing returns.
     
  5. davenn

    davenn Moderator

    13,668
    1,891
    Sep 5, 2009
    hi qweets

    here's a typical circuit layout for a 7805 (7812 etc)
    showing capacitor values and the protection diode across the regulator

    [​IMG]

    NOTE: --- the 2 x 100nF caps should be soldered as close to the regulator case as possible.
    They are used to stop any possible oscillations produced by the regulator

    cheers
    Dave
     

    Attached Files:

  6. qweets

    qweets

    48
    0
    Sep 26, 2010
    thanks very much guys,

    i've never seen a diode across like that before, i shall give it a try .

    Really appreciated,

    Have a great week : )
     
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