Negative power

Discussion in 'General Electronics Chat' started by danrulz98, Jan 6, 2014.

  1. danrulz98

    Thread Starter New Member

    Sep 17, 2012
    15
    0
    Hello,
    I'm trying to find a replacement power supply for an old game machine. The original is a giant brick, and I think a modern switching power supply can fit inside the unit its self.
    But, I've been searching around and I can't really find a solution.
    I need:
    + 12 volts at 0.3 amps
    + 5 volts at 0.9 amps
    - 5 volts at 0.1 amps

    and all sharing a common ground.

    I was thinking I could use one of those generic 12 volt power supplies and a LM7805 and a LM7905, and while that would provide the + 12 and +5, the LM7905 just doesn't work that way.

    Since the 3 of those share a common ground, I don't think I can run the 5 volt supplies off of the 12 volt supply at all.

    So now I'm wondering what my best option is? To use a little 12 volt power supply and two iPhone chargers (5 volt very regulated power supplies)?
    Ideally, I'd like to have just one power supply that can provide all of that. It's not a whole lot of power that's needed, especially on the -5 volt rail.

    I'm just looking for the simplest answer at this point.
    Thank you!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
    2,369
    How come it was a 'Giant Brick' for that small a VA?
    You can get wall wart types that will cover that current for <$4.00.
    rig three of them up, 1-12v 2-5v with a short power bar or 4 socket surface mount outlet box, and set up a terminal strip.
    The other for a combined one is get a small toroidal transformer and wind the secondaries, very few turns for each.
    3 pin regulators 3 small bridges and three caps.
    Max.
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,387
    497
    Seems like computer power supply can do that easily.

    The one I am looking at has following on its label:
    +5 V, 20 A
    +12 V, 10 A
    -5 V, 0.5 A
    These meet and exceed your requirements.
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    An example size wise is this one.
    5' X 3" X 1.5"

    12@2.5
    24@1
    5@3
    -5@.5

    Not quite what you need.
    I would think you could find one half this size.
    Maybe not. Harder to find than I first thought
     
  5. danrulz98

    Thread Starter New Member

    Sep 17, 2012
    15
    0
    I'm pretty sure it's not a switch mode power supply... It weighs just over a pound.
    Having 3 wallwarts like that is alright then? Even with a common ground to all of them?

    And yeah, I know a computer power supply will do it, but those are quite large and expensive comparatively.
     
  6. danrulz98

    Thread Starter New Member

    Sep 17, 2012
    15
    0
    I also found this, which seems to take +5v in and gives you + and -5v out. $5 on Mouser though..
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    How about this one @ $5.95?


    Outputs: #1: +5V @ 3A #2: +12v@ 2A #3: -5V @ .35A

    Overkill?
     
  8. danrulz98

    Thread Starter New Member

    Sep 17, 2012
    15
    0
    Slightly, but there's nothing wrong with that. Where is that?
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
  10. danrulz98

    Thread Starter New Member

    Sep 17, 2012
    15
    0
    Awesome, that's perfect! Thanks.
     
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