quick question, broken pot?

Discussion in 'General Electronics Chat' started by Adamf001, Sep 4, 2012.

  1. Adamf001

    Thread Starter Member

    Sep 5, 2011
    67
    2
    I'm building a power supply like many people have, using a simple LM317 circuit, the first breadboard try didn't work, but do first goes ever work, so using a multimeter I tried to find the problem, as soon as I touched the wires from the power supply with the multimeter probes my pot sparked, but since I have tried making this circuit It doesn't work...

    is it possible to 'break' a potentiometer? or am I just incapable of prototyping circuits on a breadboard?

    any tips on using breadboards?
     
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    Pots can be "dead spotted" by running too much current through too short a section of the element. You can test the pot with a meter. Make sure you have the regulator connected correctly as it sounds like you may have attached the pot to the input or output instead of the adjust terminal. Beware that some datasheet example circuits show the pins in an orientation that does not match the actual package. If you're using a TO220 size device, twist each of the leads 90° near the body so it's easier to fit into the breadboard socket without stretching the socket contacts.
     
  3. ramancini8

    Member

    Jul 18, 2012
    442
    118
    A common problem for newbies is to wire the pot as a variable resistor to the base of a transistor. When turned to the end the current is not limited and the transistor blows.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,437
    3,360
    When wiring a pot as a variable resistor it is a good idea to include a fixed resistor in series to limit the current to a safe level.

    Also wire the center tap to the unused terminal for security in case the center wiper loses contact. This way the pot would exhibit maximum resistance instead of an open circuit.
     
    PackratKing likes this.
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