LM317 with low volt cut off or simlar

Discussion in 'General Electronics Chat' started by kiwisoundguy, Nov 10, 2010.

  1. kiwisoundguy

    Thread Starter New Member

    Sep 14, 2010
    Hi there,

    I am building a simple DC PSU. 18v DC in 12v DC out. I have been using an LM317 and its been fine. Now I require the output to trun off / cut out if the output or indeed the input voltage drop below 12v. Is there a simple IC or transitor that I can use. My current draw is 200ma max.

    Thanks in advance for your help!
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    Shouldn't be too hard to adapt a zener possibly with a transistor into the adjusting leg to set it to minimum should the condition occur, a complete cutoff could also be designed into the 18V coming in line but you'd need a small amount of delay so it would allow the regulator to start up at first.
  3. kiwisoundguy

    Thread Starter New Member

    Sep 14, 2010
    Thanks for that. Would you able to suggest said zenner and transistor please?

    Cheers, Ben
  4. Artikbot


    Nov 7, 2010
    I believe any 12.1V Zener will serve the purpose. Since it's just a signal for a comparator, I guess no high power is needed.