7812+ regulator problem

Discussion in 'General Electronics Chat' started by 1-3-2-4, Jun 3, 2013.

  1. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    I think I have a problem with a new regulator.. between pins 1 & 2 I'm showing continuity should that be right? My power supply keeps going into protection mode.

    Pin 1 is (+) Pin 2 is (-) and 3 is the output
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    No there should not be continuity between any pins. There should be a diode from output to input IIRC, check the internal diagram of it.
     
  3. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
    194
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    Not seeing a diode it's a LM7812C
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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  5. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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  6. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    OK it turned out to be my PCB I did not notice in a row they were all connected..

    Ok so I separated them but I have a new problem.. my supply voltage for testing is 13.4v and after a few seconds the regulator gets too hot to touch, no load just straight voltage regulation, what could cause that?
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It's dissipating too much power. To help with that, you can 1. reduce the load, 2. decrease the input voltage, 3. add a heat sink, 4. add a fan. However, all this may be worthless if your circuit is wrong.

    Post a schematic.
     
  8. 1-3-2-4

    Thread Starter Active Member

    Dec 26, 2008
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    No I found the issue.. I have no load at all and input voltage is 13.4V on a 12V regulator.. that's not much heat at all..

    Nevertheless the regulator must be oscillating my wire length is 10 inches long and I don't have a 0.1uF cap on the regulator.

    Just turning it on with nothing connected to the IC socket it's heats up to shutdown temp within a few min.
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Post a schematic.
     
  10. Shagas

    Active Member

    May 13, 2013
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    Continuity between pins is usually a sign of a short in the ic , meaning you either accidentally screwed it up when first connecting it or maybe they just gave you a defective one. Or maybe it was damaged by very high static (if that's possible with this IC)
     
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