24v control/test box

Discussion in 'The Projects Forum' started by servo, Oct 28, 2011.

  1. servo

    Thread Starter Member

    Aug 11, 2011
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    Hey, all. I've got a project that I need to do for work, but I'm not sure where to start. I need to design and build a box that will run on and put out 24 VDC, but also be able to put out +/- 10 VDC. It will also need to have test points to monitor the signals on the pins of a 12 pin connector. It's a breakout box combined with a power supply and control function, I guess. My main problem is the power supply. How do I pull +/- 10 VDC from +24VDC?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    Just reverse the leads.. We use a +48VDC supply at work and just by reversing the leads you get +48 or -48VDC.

    So a 24 V isolated supply plus a 10V regulator circuit.
    What current level do you need for the -/+10V?
     
  3. servo

    Thread Starter Member

    Aug 11, 2011
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    Never more than 2 amps. I had a problem with this circuit before where there seemed to be a grounding issue. I could not get the circuit to work properly and I was getting some strange voltages where they shouldn't be. This was using a 12V regulator and a switch to reverse the leads.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I remember that thread. Here: http://forum.allaboutcircuits.com/showthread.php?t=58057

    If you must power the +/-10v supplies with 24VDC, you will need to use switching regulators that have galvanically isolated outputs; something like this:
    http://search.digikey.com/us/en/products/PTB78560CAH/296-20363-ND/789181

    If you have anywhere from 100VAC to 240VAC available, you could probably use a pair of these:
    http://www.mpja.com/12VDC-2A-Regulated-Plug-Supply-Jasper/productinfo/18776+PS/
    12v, 2A regulated switching plug supplies.
     
  5. servo

    Thread Starter Member

    Aug 11, 2011
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    Thank you, SgtWookie. And thank you for your previous help. I'll look at the links you sent me.
     
  6. servo

    Thread Starter Member

    Aug 11, 2011
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    Last edited: Oct 31, 2011
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Well, with 24v in, the PD412 model will give you ±12v @ 40mA maximum; is that going to be sufficient? (better stay at 80% or less of that maximum rating; so <=32mA)
     
  8. servo

    Thread Starter Member

    Aug 11, 2011
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    The current draw on the control circuit is negligible. 2 or 3mA maximum. 40mA should be more than enough, not to mention a heck of a lot cheaper.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Note that you need to maintain a minimum load on those supplies.
    Use a 2.4k resistor from each out ±12v terminal to the output common terminal.
     
  10. servo

    Thread Starter Member

    Aug 11, 2011
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    Ah, yes, I see that. I'll be sure to do that.
     
  11. servo

    Thread Starter Member

    Aug 11, 2011
    31
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    The isolated converter works like a dream. Thanks for all the help!
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Cool beans! Glad you finally got it working. ;)
     
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