Regulator short circuit

Discussion in 'General Electronics Chat' started by MurNesty, Sep 11, 2012.

  1. MurNesty

    Thread Starter New Member

    Jul 28, 2010
    3
    0
    Hi,

    I found tat LM1117 has a short circuit between output pin and ground when power on. But only in reverse direction - Multimeter positive to regulator ground and multimer negative to regulator 3.3V.

    I read the diagram seems like no diode between output and ground. So what cause the short circuit?

    Regards,
    Murnesty
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    Are you trying to measure resistance in a circuit while being powered?
    Hope not, because you cannot do that.
     
  3. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    1) trying to use an ohm meter on a powered circuit.
    2) applying the wrong polarity to the output with an ohm meter.

    Why would you even try this?
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Every monolithic IC regulator has a "body diode" from output back to input which will read like a "short" on a cheap meter.
     
  5. MurNesty

    Thread Starter New Member

    Jul 28, 2010
    3
    0
    Erm I'm using the multimeter's measure short. I doing so to test whether my circuit is short after power up. Heard my colleague says a zener diode will caused regulator short(the zener diode is used to protect reverse power polarity).

    So it mean I can't use multimeter to test short when power on but only can test while power off?
     
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