power supply problem...

Discussion in 'General Electronics Chat' started by WAN24, Jan 15, 2008.

  1. WAN24

    Thread Starter Member

    Jun 27, 2006
    21
    0
    gud day sir!!

    im working on a power supply with 3 different regulators to power my project(op-amp circuits).. +5v, +12 and -12v... the input for the rectifier is 12v 750mA AC.. (the schematic is attached) the problem is that im only getting 5v on the outputs... i've checked the circuit board, changed the regulators... and still, the same problem :confused: .. any suggestions or corrections on my circuits...

    tnx in advance!!!
     
    • ps.JPG
      ps.JPG
      File size:
      39.7 KB
      Views:
      52
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The 7912 cannot change the polarity of supplied voltage. You need to provide negative voltage in to get negative regulated voltage out.

    Continue to use transground as ground, but do not connect the rectifier to ground - instead connect rectifier negative to the 7912.

    I have no idea why the 7812 would put out 5V. Are you certain of your components?
     
  3. WAN24

    Thread Starter Member

    Jun 27, 2006
    21
    0
    tnx sir for the immediate reply... i only designed this circuit... im going to changed the input for 7912... any more suggestions or corrections on my circuit sir? again.. thank you so much sir!!
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    On the schematic, the AC is applied to the DC output terminals of the bridge rectifier. You need to look at the schematic (and the circuit) and make sure the AC goes to the right places on the bridge.
     
  5. WAN24

    Thread Starter Member

    Jun 27, 2006
    21
    0
    ooopppsss.. my wrong... but, i already checked it and change the terminals... and still problems above persist.. but maybe the 7912 is solved.. only the 5v output for the 7812 is the problem...
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You need to update the schematic and repost it. The filter capacitor on the bridge is incorrect, the DC voltage comes from one line, meaning there is no negative voltage, and so on. We can't tell what might still be wrong until the schematic is corrected.
     
  7. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    Check you connections per the attached.

    Also, the transformer needs to be ~24VAC secondary, or a dual 12VAC secondary connected in series. A 12VAC secondary that is center-tapped will only provide 6VAC to each side of (+) and (-), which will be about 9VDC or less, and this is probably why the 12V output is low.
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Where are my posts?
    Oh, they are on another website.

    I think the regulators are destroyed from having the bridge rectifier connected wrong.
     
  9. WAN24

    Thread Starter Member

    Jun 27, 2006
    21
    0
    ok sir.. thanks for the help... im going to change my circuit and tell you what happen... again, w/ due respect.. thank you guys..
     
Loading...