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Generating a negative voltage from a +24V DC source?

  1. Feb 20, 2010 #1
    I have a standard AC-DC rectifier that gives me +24V, 12.5A power supply. Now, I've a problem... what's the simplest way to generate a negative voltage between the rails?

    This may sound silly but I really thought I could just use the power supply as I would do to generate a positive voltage, but just run an extra wire to ground the end with the higher potential. Maybe I'm misunderstanding how the power supply works because it clearly didn't work.

    I ran a search on "generating negative voltage" and saw a number of solutions involving ICs. But these have been proving quite expensive. I found it simple to invert the voltage, but maintaining a 12.5A output will be a problem. Will be great if someone can recommend me a solution! Thanks.
  2. jcsd
  3. Feb 20, 2010 #2


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    You'll need a center tapped transformer to get a split supply.
  4. Feb 20, 2010 #3


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    Do you want to:

    Have a negative supply instead of the positive one?

    Have a Positive and a negative supply, both 24 volts at 12.5 amps? (but not 12.5 amps from each at the same time)?

    Have your 24 volts become plus 12 and minus 12? ie a split supply with a ground in the middle?

    Have an additional negative voltage as well as the plus 24 volts, but the negative supply can be at low current?
  5. Feb 20, 2010 #4
    Last edited by a moderator: May 4, 2017
  6. Feb 21, 2010 #5
    ^dlgoff: I'll preferably not build another power supply =/ But thanks nonetheless for letting me know about the center-tapped transformer... I'll use that someday if I need a low-noise application.

    ^vk6kro: I'll like to have the first one: a negative supply instead of the positive one. My supply actually gives me 3 x 24V rails and 3 x 0V rails. I was thinking of something along what Bob S suggested - using a inverting circuit based on a DC-DC converter after one of the 24V rails.

    It will be much easier for my application if I can get a higher current than 2A though; do you have an idea for that?

    ^Bob S: Cool, you always have something close to what I need. The -12V/2A output topology seems good... I think I'll use that if there's no other alternative.

    What do you think of this LM22677? http://www.national.com/pf/LM/LM22677.html#Overview [Broken] I have it to produce 12V/5A... any idea how to get it to -12V/5A?


    Thanks everyone!
    Last edited by a moderator: May 4, 2017
  7. Feb 21, 2010 #6
    Oh wait, problem solved! I was referring to the wrong page of http://cds.linear.com/docs/Datasheet/3758f.pdf [Broken]

    Much thanks for everyone's input!
    Last edited by a moderator: May 4, 2017
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