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voltage regulators - in parallel?

Discussion in 'Electronic Basics' started by anonymous, Oct 9, 2004.

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  1. anonymous

    anonymous Guest

    can multiple voltage regulators be run in parallel? Each terminating in a
    separate output? IE - the inputs are tied together but the outputs are
    separated.

    I put together a small board hoping to break an 18V 400mA wall wart into 4
    9V sections. Im getting some wierd output (8V at the Vout for the
    regulators) thats making me wonder whether my concept is fundamentally
    flawed.
     
  2. CFoley1064

    CFoley1064 Guest

    Subject: voltage regulators - in parallel?
    You might first check how much current you're using. Too much, and you might
    be bogging dowm the wall wart. If not, there's no problem with using the 18V
    to make multiple 9V supplies, as long as you don't connect their outputs
    together (double-check your wiring here). (see other post for more
    information).

    Good luck
    Chris
     
  3. anonymous

    anonymous Guest

    You might first check how much current you're using. Too much, and you
    So what would be causing the Vout to drop to 8V? its consistent across all 4
    regulators.
     
  4. Bill Bowden

    Bill Bowden Guest

    Yes, you can connect 4 inputs of 4 regulators to the same source,
    if the regulators have different loads. But the total load
    current of all 4 outputs can not exceed 400mA before the
    input will start dropping.

    How much is the load current for each output?

    -Bill
     
  5. me

    me Guest

    So what would be causing the Vout to drop to 8V? its consistent across
    Operator error?
     
  6. Gareth

    Gareth Guest

    How much current are you drawing from the four outputs? As Chris said,
    if you are drawing too much current the wall wart output voltage will drop.

    Can you measure the voltage at the input to the regulators? It will
    need to be >12V (approx. depends on the regulator) for your regulators
    to operate correctly.

    Gareth.

    --
     
  7. anonymous

    anonymous Guest

    Yes, you can connect 4 inputs of 4 regulators to the same source,
    For the test I ran I was drawing ~5mA. But I read 8V at the regulators when
    there is no load at all.
     
  8. What does the input voltage drop to when the output voltage is 8?
     
  9. Maybe its time for a new battery in that multimeter?

    A good test would be to check the voltage across a 9v battery with the
    same meter.

    The other possibility is that your regulators are either bad, or they
    are oscillating. Put a small load on them, and also use a 0.01uF (10nF)
    cap across the output.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
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