S.o.s (top urgent)

Discussion in 'The Projects Forum' started by shorabkareem, Mar 20, 2013.

  1. shorabkareem

    Thread Starter New Member

    Jan 19, 2012
    shall greatly appreciate if a anybody can answer my queries.

    this is a DC supper supply (circuit diagram attached ) which i did few years back for my electronic class project. at that time i didn't not face any technical issues. But at present when i did the same project with the same schematic guide i get numerous issues.

    1. number of my circuit got burnt (10 k pot) when i try to adjust the voltage ? why did it happen? can i have detailed explanation.

    2. Once when everything seems okay with the circuit. there was a wrong reading (shows 5v when it should be 1.25v) when you adjust 10 pot to minimum.... Can anybody explain to me why?

    3. finally after going through numerous website i found a solution to the burning potentiometer issue, that is to insert a
    1N4007 diode between adjustable pin + out pin and used another diode between out pin + in pin.... will this save me from
    further trouble..... please advice.

    thanks in advance for your co-operation
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Adding diodes should have no effect on the pot. If the pot is burning, that means it can't be a 10k pot. No way there's enough voltage available to create the power to burn it. Also, it probably is wired wrong. Burning a pot takes current. It's possible the 317 device is wired wrong and you are getting current flow back through the substrate. Infinite possibilities, but the schematic as drawn should not burn the pot.
  3. DickCappels


    Aug 21, 2008
    If the transformer, bridge, and fuse are wired as shown in your diagram, the fuse should have blown unless it is grossly over-sized.

    The rectifier in the lower right-hand corner of the bridge shorts the transformer every half cycle of the AC line. Just thought I would mention it.

    The circuit as shown should be fine with or without the diodes. Most likely the circuit is wired incorrectly. My guess is that you have the output and ajust terminals reversed and when the voltage gets lower, its because the LM317 is going into current limit (and burning the pot).
  4. MrChips


    Oct 2, 2009
    Choose a better title next time - The Title Police.
  5. MrChips


    Oct 2, 2009
    1) The fuse goes on the input side of the transformer.

    2) Your bridge rectifiers are wired incorrectly.

    3) You need decoupling capacitors on the input and output of the regulator.
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
    Also use a dictionary to check spelling. Unless you really meant supper. - The spelling Police.