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DC-DC converters

Discussion in 'Electronic Design' started by js, Jul 16, 2003.

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  1. js

    js Guest

    A follow up from my "Converting PCB from AC to DC" thread ... we have a
    control board that runs off AC which is rectified and regulated to +12VDC
    and -12VDC. I am converting this to run off a +12VDC regulated supply
    instead of the AC and following the recommendations to use a DC-DC converter
    to get +/-12VDC from a 12VDC input supply.

    Question: DC-DC converters with come in 12VDC single output or in +/-12VDC
    dual output. Is there such thing as a single channel -12VDC converter?
    With this I could use the existing +12VDC input as my +12VDC 'leg' and use
    the converter to get the -12VDC 'leg'.
    that I need 100mA on the + leg and converters that supply this much juice
    have a minimum rating of 12mA. At times my - leg only draws 7mA.

    What to do?
     
  2. Jon Elson

    Jon Elson Guest

    Of course. You need an isolated 12 V to 12 V converter. Connect the

    output + to ground, and the output - to the -12 V load.

    Jon
     
  3. js

    js Guest

    I was hoping that's how it worked. I read the spec sheets etc but they
    never actually come out and say this.
    thx
     
  4. The only specs necessary are that the output is isolated from the
    input and the isolation is good for a lot more than 12 volts.
     
  5. Afraid so. You need something like a pair of 13 volt zener diodes
    across the supply, to derive a rough center voltage between the ends
    of the 24 volt rails. I think that if you trace the current through
    the series regulators you describe, it would be required, under some
    circumstances for the current to go the wrong way through the pass
    transistor.
     
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