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dual supplies

Discussion in 'General Electronics Discussion' started by leeb_965, Apr 28, 2012.

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  1. leeb_965

    leeb_965

    34
    0
    Feb 5, 2012
    hi,

    how can i get a positive and negative voltage out of a single 3 port dc power source (+, -, ground)?

    I need +6V and -6V for an op-amp
     
  2. timothy48342

    timothy48342

    218
    1
    Nov 28, 2011
    Explain more. It sounds like you already have a + and - voltage if your "single 3 port" source is +. -, 0.

    Describe your source more.
    -tim
     
  3. leeb_965

    leeb_965

    34
    0
    Feb 5, 2012
    yeah it is, see the attached jpeg.
     

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    This is a single-ended power supply.

    You need to either set it to 12V and create a middle rail or get two of them and connect them together to create a double-ended power supply.
     
  5. leeb_965

    leeb_965

    34
    0
    Feb 5, 2012
    hi,

    so how would I create a middle rail then?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    It depends on the current you need. It could be as simple as a couple of resistors with capacitors across them, or an op-amp driving a pair of transistors.

    This site evaluates a number of options.
     
  7. leeb_965

    leeb_965

    34
    0
    Feb 5, 2012
    Can this be done with just the resistors? I need dual supply for a LF353N opamp which can go up to +-18V max. Im not sure if it needs to be a perfect balance between +6V and -6V
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    10,547
    2,349
    Nov 17, 2011
    Using resistors is an option as long as the current on the 0V rail is very small. If, however, you are going to drive e.g. an amplifier, you need a more powerful solution as *steve* suggested.

    Can you post the model of this power supply? While it shows only a single readout for voltage, it still could be a dual supply. Otherwise I see no reason for the GND socket.
    You can make a simple measurement: set the power supply to 6 V. Measure from "-" to GND, from "+" to GND. If the first measurement gives -6 V and the second measuremnet gives +6 V, then it is a dual supply. If the measurements give +-3 V, then it is a single supply (In that case I'm wondering what to do with the GND socket).

    Harald
     
  9. davenn

    davenn Moderator

    13,668
    1,891
    Sep 5, 2009
    My twin single rail PSU also has GND sockets

    The reason is probably the same as the one shown by the OP
    the negative is likely to be floating above the chassis where the GND socket is
    connected to the chassis and hence EARTH :)

    Dave
     
  10. davenn

    davenn Moderator

    13,668
    1,891
    Sep 5, 2009
    nice supply :)

    looks like it is as I described for my one

    look through that link that Steve gave above there are examples down the page in there of how to turn a single rail supply into a dual one and ifthe only thing you are powering from it is the Op-amp then you shouldnt have a problem with current requirements :)

    Dave
     
    Last edited: Apr 29, 2012
  11. leeb_965

    leeb_965

    34
    0
    Feb 5, 2012
    So I could do this without the capacitors?
     
  12. davenn

    davenn Moderator

    13,668
    1,891
    Sep 5, 2009
    did you look through that cct collection in the link ?

    most of the examples use at least 1 cap some of them use 2

    Dave
     
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