Adjustable voltage regulator protection question

Discussion in 'General Electronics Chat' started by munuainen, Jul 30, 2014.

  1. munuainen

    Thread Starter New Member

    Jun 13, 2014
    LM317 datasheet, p.6-7 under the heading 'Protection':

    I can understand the purpose of D1 offering a safe discharge path for C1. D2, however, raises an immediate question: if there truly is an internal "50Ω resistor which limits the peak discharge current", I don't see the purpose of D2 for C2 discharge protection. Regardless of the output voltage, C2 will be charged up to 1.25 volts, tops. In which case the theoretical peak discharge current would yield 1.25V / 50Ω = 25mA, and that's not going to hurt anyone.

    What's wrong with the above logic?

    EDIT: Now I feel stupid. It's not the Vadj-GND but Vout-Vadj that's 1.25V. In that case, Vadj-GND (and C2) can be anything from 0V to Vout-1.25V.

    If only there was a way to delete the entire topic...
    Last edited: Jul 30, 2014
  2. tom_s


    Jun 27, 2014
    me thinks we all been guilty of trying to put the square peg in the round hole.

    thanks for being human :)
  3. wayneh


    Sep 9, 2010
    Haha, we all saw you naked. Welcome to the club. :p