positive / negative power supply from two separate units?

Discussion in 'General Electronics Chat' started by unprovoked, Apr 2, 2009.

  1. unprovoked

    Thread Starter New Member

    Apr 2, 2009
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    I would like to power a circuit with an op-amp (acting as voltage to current converter) and two transistors (acting as current amplifier) with +12V and -12V. The output current can be as high as 3A. So, I need a dual power supply +12/3A and -12/3A.

    Can I use two table-top power supplies (Jameco #220442; regulated switching), and reverse the leads on one of them? A previous post stated something relevant, but I don't completely understand:
    "This does not apply to non-isolated DC power supplies where one terminal is hardwired to a power common, (or neutral) connection and you are not free to swap polarities simply reversing connections to your application."
    How do I know if the table-top supply I'm interested in has a "terminal hardwired to power common"? It's datasheet says:
    2.5. 2-wire input AC line (Line Neutral)
    3.11. The DC ground will be isolated from the AC neutral and AC line

    I am not an engineer, so please try to explain in the simplest terms possible.

    Thank you!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The statement -
    - tells you that the output is not hardwired to the AC wiring. You can stack the supplies to get your +/- 12 VDC.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I can't speak specifically to your supply, but most lab quality supplies have floating outputs, where you can tie either end to ground...or another supply. I imagine yours would work fine.

    eric
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    By the way, if you want a really cool project to work on, you can build a tracking regulator...it's a bipolar supply that always keeps the ground at precisely the midpoint. Great way to learn about op amps~

    Eric
     
  6. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    http://www.datasheetcatalog.org/datasheets/400/501050_DS.pdf

    You could clone this thing using garden variety op-amps for the feedback.


    eric
     
  7. unprovoked

    Thread Starter New Member

    Apr 2, 2009
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    Thanks for the incredibly fast responses and also for the link to mpja.com (which is so much cheaper).

    For other similar supplies, if I can't find a spec sheet, how can I tell if DC ground is isolated or not? For example, how do you know if http://www.mpja.com/prodinfo.asp?number=17261+PS or http://www.mpja.com/prodinfo.asp?number=16918+PS is isolated and thus the leads reversible?

    Out of curiousity, what would happen if the DC ground was not isolated and someone tried to reverse the leads?
     
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