Creating postive and negative voltages using LM350 positive regulator ?

Discussion in 'General Electronics Chat' started by iinself, Jan 24, 2015.

  1. iinself

    Thread Starter Member

    Jan 18, 2013
    69
    0
    Hi,
    I am trying to create positive and negative 35V from 2 58V capacitor tied in series in the PSU unit of a old receiver. Will the attached circuit work for that?

    Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    What attached circuit?
    You can't create positive and negative voltages with just capacitors.
    You can split the voltage with a virtual-ground circuit to give a plus and minus voltage with respect to the virtual ground. Is that what you want to do?
     
  3. iinself

    Thread Starter Member

    Jan 18, 2013
    69
    0
    Sorry forgot to attach, it should be there now. thanks
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    You can't doing that way, what you did was wrong.
    You need to using LM333 to replace LM350 for the negative side, please see the page 8 of LM333.
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    The circuit you show requires separate isolated grounds for the circuits that will be using the plus and minus voltages.
    Is that okay for your requirements?
     
  6. iinself

    Thread Starter Member

    Jan 18, 2013
    69
    0
    It is for LM3886 amp, I am trying to generate + and - 35 V with common ground for the amp.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,528
    1,248
    Nope. What you drew is an incorrect version of an old trick for using positive 3-terminal regulators in a +/- power supply. As pointed out in #5, the circuit requires two isolated sources because the negative regulator is regulating the ground, not the - output. This usually comes from two isolated transformer secondary windings. If your +/- bulk DC sources already have a common ground, then you need a true negative regulator IC as in #4.

    ak
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    The combination of a LM350 and an LM333 will not work with a virtual ground if the plus current exceeds the minus current (as it will be with the LM3886 on the positive signal peaks) since the LM333 cannot sink current under those conditions.

    The best way to use the LM3886 with a single supply is shown in Figure 3 of the LM3886 data sheet.
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    @crutschow , you must have an other datasheet than the one I have.
    The single powersupply circuit is figure 2 on page 6 of the one I have.

    Bertus
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    A remark on your schematic:

    [​IMG]

    Bertus
     
  11. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    Yes, I looked at the TI datasheet, which I should have specified.
     
Loading...