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Generating a negative voltage - charge pump or switchmode?

Discussion in 'Electronic Design' started by Michael Brown, Apr 10, 2008.

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  1. One of my pet projects requires a power supply that gives both +48 VDC
    and -48VDC (from mains), no more than 3A on each rail. After a bit of a
    look, it seems that such power supplies are rather rare, especially here in
    Australia. Maybe I'm using the wrong search terms, but I can't even find a
    *single* supply that puts out both +48V and -48V. However simple +48V
    supplies are relatively easy to get hold of. So, my idea was to tack a DC-DC
    inverter onto the output of the +48V supply to get the -48V.

    Now, this is an area I'm not too familiar with. I've made simple
    capacitor-switching charge pumps before, but for ten's of mA, not 3 A. And
    I've never done a proper switchmode supply. My question is - for this
    situation, which will be easier to get working: a charge pump or a
    switchmode inverter? Strict regulation is not an issue - the 48V actually
    goes into another DC-DC converter (don't ask ...) which will hopefully fix
    any slight discrepancies in the -48V output.

    Or, if someone has a link to a +/-48V power supply that you can buy in Oz,
    let me know!
  2. Phil Allison

    Phil Allison Guest

    "Michael Brown"
    ** Err - you need to buy two of them.

    Then wire one of them with the + to common.

    ....... Phil
  3. I thought this made switchmode supplies unhappy? Or is that just an old
    wives tale?
  4. Phil Allison

    Phil Allison Guest

    "Michael Brown"

    ** Try reversing the phase and neutral on that one - should even things up
    a bit.

    ....... Phil ;-)
  5. Rich Grise

    Rich Grise Guest

    Trying to run them _in series_, i.e., if he was looking for a plain 96 VDC,
    then it probably won't work. But with the center point grounded, each
    supply will have its own load, albeit a lot of the time they'll be shared,
    but each supply does its own regulation and doesn't have to worry about
    the other.

    Just be sure that the supplies have an _isolated_ output!

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