LM732 Voltage Regulator

Discussion in 'General Electronics Chat' started by KCHARROIS, Jan 10, 2013.

  1. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Hello,

    I'm looking at IC's that would work great for my amp and a teacher recommended using the LM732. I would like to use the same configuration like the the one below but I also need a negative supply voltage. Could I use the same circuit but now instead use (+) terminal as ground and the (-) terminal as Vee?

    Thanks

    [​IMG]
     
    Last edited: Jan 10, 2013
  2. crutschow

    Expert

    Mar 14, 2008
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    If you have an isolated (not common) negative voltage source, then yes you can use the same circuit. Just note that you are still regulating the positive side of the voltage (now considered the common), which is fine as long as you have an isolated source.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You would be much better off with am LM337 (neg) and LM317 (positive) voltage regulators. They are simple 3-pin devices specifically designed to decontrol a split rail system with variable voltage control.
     
  4. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Not quite sure what you mean???

    What I'd like to do is this...
     
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  5. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    While I happen to really like the many good qualities of the LM723 it is a very involved part to use when compared to components designed even 20 years ago.

    I'd never use a positive regulator to regulate a negative voltage. It makes my head hurt trying to see what path currents take and can the negative side regulator actually regulate the current?

    What exactly are you working on, what kind of amp?

    (BTW, as drawn your dual regulator is a big short! Some connections need to be parted, some need to be connected.)
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The DATASHEET says it can be used for pos or neg voltage regulation. However, the external circuitry, including the pass resistor (PNP) must be adjusted for the negative rail. Luckily, the whole neg supply regulation is at the top of page 13 of the DATASHEET.

    http://www.mouser.com/ds/2/389/CD00001008-10101.pdf
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Your combined circuit will work, as long as the two sources are isolated with separate transformers or output windings but with the commons not connected together then there is no short.

    I built a dual lab supply many years ago that have a very similar circuit. I happened to use two identical negative regulators operating from isolated transformer windings to get the positive and negative. It makes no difference to (and can't be detected by) the outside world as to which side of the output has the series regulator. All you see is the voltage across the two output terminals.

    Actually you can connect either pair of outputs together for the common to give either a plus and minus voltage or two same polarity outputs in parallel for more current. Many commercial lab supplies with isolated multiple outputs do the same thing.
     
  8. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    I need a power supply for my audio amplifier that requires 5amps at a 4 ohm load. Would the LM337 (neg) and LM317 (positive) work fine for this?
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Not directly, they can only handle 1.5A. You can add a pass transistor to boost the current. There are examples in the DATASHEET. Otherwise, higher amperage units are available (LM 350).
     
  10. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Yes sorry i forgot to mention I would add pass transistors. So would this work well for amp such like this one?
     
  11. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes, it will work. However, most audio amps do not have voltage regulators, just large filter capacitors. Why do you want/need

    Your amp already includes constant current sources to regulate current (Q7, Q8, Q19, Q20) on the voltage gain part of the circuit so the circuit doesn't need voltage regulation. The power transistors are voltage followers so they don't need voltage regulations.
     
  12. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Well my current power supply consist of a bridge rectifier and 4, 10000uF caps. Will this do just fine?
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes. Add one 0.1uF ceramic cap in parallel with the 10000uF caps to be better but, if those are not immediately available, your current setup will be fine. This assumes you have a 40 volt, center tapped transformer (or two 20 volt transformers wires in series).
     
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  14. ScottWang

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    Aug 23, 2012
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  15. timescope

    Member

    Dec 14, 2011
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    I also agree that a regulated supply is not needed. Some form of short circuit protection for the output stage of your amplifier would be nice.

    Timescope
     
    Last edited: Jan 11, 2013
  16. bratsuzao

    New Member

    Jan 11, 2013
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    then yes you can use the same circuit. Just note that you are still regulating the positive side of the voltage[​IMG]
     
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