Question about Voltage Regular

Discussion in 'General Electronics Chat' started by beeson76, Jul 12, 2010.

  1. beeson76

    Thread Starter Member

    Apr 19, 2010
    185
    1
    I have a Voltage Regulator. It is a L7805CP from ST. I want my circuit off of a 7.5V DC Adaptor. It is Tip Negative. Should I run the tip to input or ground on my Voltage Regulator, and vice versa with the outside. I wonder because I hear that voltage actually comes from negative side. Just wondering. Also if I hook my voltage regulator up backwards, will that ruin it? Thanks.
     
  2. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    If it is centre pin / tip negative, the tip needs to go to ground, and the outer connection needs to go to input.
     
  3. beeson76

    Thread Starter Member

    Apr 19, 2010
    185
    1
    Will it ruin it if I hook it up backwards?
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Yes. Yes it will. You also need to use decoupling caps on the output.. I would use on on the input as well. READ THAT DATASHEET. It will have all you need too know.

    If you are having a problem figuring out which part of the AC adapter plug is (GND), use a multimeter.

    If you put the black lead on one part and the red on another (Set to read DC Volts)
    If you get a (-) negative number, you have them backwards, the one with the red probe is (GND).

    If you switch the probes, you should get the same number, but positive.
     
  5. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    It depends if you hook it up backwards whether it will be damaged.

    Also, it depends on what you mean by backwards. If you mean applying a voltage on the output pin there should be no harm.

    If you mean applying a negative voltage with respect to ground, then that's different. Generally I've found with a 7805 it just heats up, but no damage is observed. However I only ran this test for 5 seconds before I felt the regulator burning my skin... (they get really hot!) The regulator could still be damaged by overheating. Of course external caps etc. could be damaged; electrolytics can explode.
     
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