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Positive and negative voltage regulators

Discussion in 'Electronic Basics' started by Horace, Feb 18, 2004.

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  1. Horace

    Horace Guest

    Hello ...

    I have a few questions regarding the V regulators :

    (1) how come some +ve regulators does not have a complementary -ve
    regulator?
    reason for asking : I am using 2 transformers to power an audio amp and I am
    using one to supply +ve and the other one -ve. I was trying to see if I can
    use the LM317/338 to regulate the +ve side and its counterpart (if any?!?!)
    to regulate the -ve side.

    .... which leads to my second question ...

    (2) can I, in general, configure a positive voltage regulator and use it
    for -ve? (I am thinking that since voltage is relative, it doesn't matter
    whether I am regulating a Vin = 9V to Vout = 5V OR from Vin = -4V to Vout
    = -8V ... etc).

    Thanks!
     
  2. Olaf

    Olaf Guest

    that's a LM337
    I was wondering about that also...

    bye, Olaf
     
  3. Horace

    Horace Guest

    Thanks ...

    However ... the LM337 has a much lower current rating than the LM338
    (something like 1.5A vs 5.0A) .... it would be nice if I can use a negative
    regulator with higher current ...

    Horace

     
  4. Olaf

    Olaf Guest

    is a LM337 in combination with a bypass transistor an idea?

    bye, Olaf
     
  5. Horace

    Horace Guest

    Yes ... I saw that kind of configuration suggested for the LM7805/7812, etc
    .... but I didn't see in the LM 338 app notes any mention of that
    configuration. However, I think it's possible =O

    My coworker suggested using two of those chips in parallel ... that should
    work too ...

    Horace
     
  6. Olaf

    Olaf Guest

    the LM317 datasheet gives an example for a currentboost using a bypass
    transistor, so the variable voltage shouldn't be a problem in itself.
    Maybe the 338 sheet doesn't mention this because the chip can already
    deliver 5 amps, and if you need more it's cheaper to bypass a 317? Just a
    guess.

    about the parallel chips: if you parallel these, do you know for sure they
    split the load equally? I'm not sure whether this can be a problem, but
    better check ;-)

    bye, Olaf
     
  7. Jamie

    Jamie Guest

    i remember some where seeing a Positive regulator being connected
    to the + side and the output being run to ground and thus the -
    out of the supply was the high side of that transformer.
    its been a while and i am only do this from memory but seems that have
    seen a LM7805 being used as a - reg but from a separate transformer
    supply.
     
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