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LM317 question

Discussion in 'General Electronics Discussion' started by polioli, Dec 10, 2013.

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  1. polioli

    polioli

    2
    0
    Dec 10, 2013
    Hi , new to circuits and I'm making a voltage regulator using an LM317 . The circuits have diodes to take any excess voltage at the output away from the LM317 . My question is why can't you just put one diode at the output to allow current to flow out but not back?
     

    Attached Files:

  2. BobK

    BobK

    7,671
    1,681
    Jan 5, 2010
    You could, but you would lose regulation since the diode will have a different voltage drop at different currents. The diode backwards from Vout to Vin is there to protect from capacitors on the output side feeding a voltage back into the output pin of the LM317 when the power is shut off. It is not necessary in most cases.

    Bob
     
  3. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Also the diode bridge output is reversed and D6, being shorted, is useless.

    Olivier
     
  4. polioli

    polioli

    2
    0
    Dec 10, 2013
    LM317

    Thanks for replies , I understand.
     
  5. davenn

    davenn Moderator

    13,424
    1,803
    Sep 5, 2009
    here's a corrected and improved circuit diag

    [​IMG]


    cheers
    Dave
     

    Attached Files:

    Last edited: Dec 11, 2013
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