Filter capacitor with 3 pin voltage regulators

Discussion in 'General Electronics Chat' started by vks_foe, Oct 11, 2010.

  1. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Can somebody please tell the purpose of using electrolytic as well as ceramic capacitors both, for filtering at the input and output of 3 pin regulators like 7805 ???
     
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  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    The smal capacitors at the in and output of the regulator are there to prevent the regulator from oscillating.

    Bertus
     
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  3. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Hi,
    Can you please explain in somewhat more detailed way, that how it prevents oscillations...

    vikash
     
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  4. DonQ

    Active Member

    May 6, 2009
    320
    11
    Electrolytic caps are good for getting lots of uF in a relatively small package, but it comes with a cost. They also have a relatively high built-in inductance. They are very good at low frequencies, where lots of capacitance is needed, but at very high frequencies, the inductance becomes a problem.

    Ceramic caps are generally not so good at getting lots of uF, but they have almost no inductance. At high frequencies only a little capacitance is needed, but any inductance would be a problem.

    Both are needed to filter both low and high frequency components of whatever non-DC components that may be present on the line.

    One large value electrolytic, paralleled with one small value ceramic... win-win.
     
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  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    The other half of that equation is regulators are high gain circuits, to quickly respond to load changes. This can lead to oscillation.
     
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  6. vks_foe

    Thread Starter Active Member

    Jan 11, 2009
    55
    5
    Thanx to all !! :)
     
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