Can you put voltage regulators in parallel?

Discussion in 'Highly Technical' started by Bulldozer2003, Dec 21, 2004.

  1. Bulldozer2003

    Bulldozer2003 Member

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    I have a bunch of 1.5A rated LM317 positive voltage regulators. If I want to provide more than 1.5A, can I put two in parallel to provide up to 3A? Do i need any diodes or anything on them to do this?

    Thanks
     
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  3. FrankSchwab

    FrankSchwab Senior member

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    see Page 20 for an example circuit. Not as simple as you might have hoped. It's just not clear to me how to do the feedback necessary for voltage regulation with multiple LM317's.

    You might check some of the earlier pages of the PDF; they show how to do higher currents with parallelled high-power transistors doing the driving.

    /frank


     
  4. PottedMeat

    PottedMeat Lifer

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    the more current you draw out of the regulator the more power is wasted, especially when youre close to its limit - youre gonna need a kinda beefy heatsink.

    and as frank said take a look at the circuits with the pass through transistor to handle high currents
     
  5. harrkev

    harrkev Senior member

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    Yes, and no.

    The problem comes in when one wants to supply, say, 8.03V, and the other wants to supply 8.05V. The 8.03V one will do most of the work and then overheat and shut off. So simply hooking them up in parallel is not really a good idea.

    But there may be a way around this. I would try the following (just as an experiment)

    1) Put a small series resistor on the output pin of each regulator. One ohm or so should be OK. Just makse sure the resistors can handle the power.
    2) After the 1-ohm resistor, tie the outputs together.
    3) Give each voltage regulator its own feedback circuitry, but put an adjustable resistor (potentiometer) in each pack.
    4) Crank up the amps with a load of some sort, and adjust so that each regulator drives the same current.

    It still might not work, but this stands a chance of working.
     
  6. Jeffyboy

    Jeffyboy Senior member

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    You could use an LM350 which supplies 3A up to 33V or so.
    But then again, if you already got a pile of LM317's...yes, run them in parallel.
     
  7. davesaudio

    davesaudio Senior member

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    in practice , it does seem to work , have seen numerous examples
    however
    I would do the series pass (pg16) or the switching configuration