Filter Caps with LM317

Discussion in 'General Electronics Chat' started by damnyankee36, Feb 16, 2016.

  1. damnyankee36

    Thread Starter New Member

    Dec 19, 2015
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    It seems that every LM317 voltage regulator circuit I see is powered by a rectified DC input. I need a simple regulator circuit that will be powered by a battery source. Can I assume that I won't need to use any input or output capacitors in this circuit since I won't be dealing with any ripple?

    Thanks!
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    No.

    The capacitors also affect the stability of the regulator circuit and its output noise. In particular, if the wire length between the battery and the regulator is more than a couple of inches, an input capacitor is required as said in the datasheet.

    ak
     
    Last edited: Feb 17, 2016
    Johann likes this.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,965
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    Always go off the datasheet information, use input and output capacitors.
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
    1,938
    218
    Running from a battery you probably will not need as much of a capacitor. On my battery powered breadboard often omit them completely if I am just using a few mA of current. 100 mA or so I might use 1 to 10 microfarads. When in doubt, use a small cap at least.
    Try it and see what it does for you. Experience is almost as valuable as theory.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
    4,850
    767
    When you using the battery input, for the power consumption, you could use LM2576-adj,3A.
     
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