split supply(help)

Discussion in 'General Electronics Chat' started by saghar19, Dec 6, 2012.

  1. saghar19

    Thread Starter Member

    Jul 16, 2012
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    I want a dual supply from a single battery.I found this circuit but i can not find tle2426.is there any other way?I want low noise and stable one for high precision design.can you help me please?
    thanks
     
  2. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    Use 2 resistors to make 1/2 the supply voltage and feed that to an opamp with a gain of 1.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Well Mouser/Digikey/Newark/Farnell all have thousands and thousands in stock in all different package types.
    You didn't put your location in your profile so we can't offer any help there either..

    http://tangentsoft.net/elec/vgrounds.html
     
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    Did you search for "Rail splitter"?
     
  5. nigelwright7557

    Senior Member

    May 10, 2008
    487
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    I would also add 10uf across the lower resistor.
     
  6. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    Depends on the impedance of the resistors. With a jfet input amp, you could get away with 100 k resistors or maybe even a megohm each. Doesn't take much capacitance to quiet that circuit down.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    I cannot think of an opamp circuit that needs a "rail splitter" with an impedance of only 0.007 ohms. Two resistors that are 100k each in series split the rail very well and a capacitor across the lower resistor filters the voltage very well.
     
  8. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    If i understand correctly,you mean rail splitter is not necessary,so when should we use rail splitter??
    excuseme if my questions are very easy,Electronic is really hard for me to understand!!!:confused:
     
  9. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    I use this divider for my circuit and it works in simulation(attached below). does it work in real?is there any error in my circuit?(its schematic of a buffer for two wired EEG active electrode).
    if my question is not clear,please tell me to explain more.
    thanks
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I do not know why your opamp has its (-) input connected to the positive supply voltage and why there is a diode from its output to the positive supply voltage.

    An EEG or ECG circuit usually uses an instrumentation amplifier IC and has the body fed with a buffered common-mode signal with its phase reversed from the picked-up common mode signal for cancellation.
     
  11. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    well,i should explain more.Its a circuit that we put right on the scalp,Its not an EEG amplifier.Its just an electrode.If you see this page you'll understand me better. http://openeeg.sourceforge.net/doc/hw/ae.html.and the reason I have chosen this circuit is that i want to make two wired electrode.
    I connected (-) input to the positive supply in order to have two wire for my electrode(one for output and one for negative supply).The diode is a level shifter.
     
    Last edited: Dec 7, 2012
  12. Audioguru

    New Member

    Dec 20, 2007
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    Their opamp is simply a high input impedance buffer with no voltage gain.
    Yours is completely different to theirs and yours will not work properly.
     
  13. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    It doesn't have gain!!It's a buffer too,but has a different design.See attachment please.I follow an ieee transaction design.
    Thanks a lot :)
     
    Last edited: Dec 7, 2012
  14. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    I wish someone could help me!:(
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    They did not use a diode so you shouldn't need it.
    Use a rail-to-rail input and output opamp.
     
  16. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    They used single supply for op amp but when i simulate theirs,does not work!!(attached)
    why??What is your idea?Here what seems to be wrong?
     
  17. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,987
    3,733
    Your circuit is completely screwed up. Something was lost in translation.

    Two resistors work well for low power circuits. Unfortunately, those to resistors do not keep the mid-point (virtual ground) at the mid-point as the power goes up on one half of the rail. Larger and larger capacitors will be needed to keep the rail balanced.

    You can easily add an op-amp to make it an active rail splitter, or ever an op-amp with pass transistors to make it high-power (if feedback is from the juction between the two transsitors).

    Let us know what you are making and the amperage you plan to drive and we can chime in with some advice.

    What is inside the box is a good start for a rail splitter. You can use two 10k resistors with your op-amp instead of the potentiometer shown in the box. Ignore what is outside of the box.

    [​IMG]
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    Your simulation software does not know about modern "rail-to-rail input and output opamps".
     
  19. saghar19

    Thread Starter Member

    Jul 16, 2012
    38
    0
    I simulated with pspice schematic. Which software is better?I just know pspice shematics and proteus for simulation.
     
  20. Audioguru

    New Member

    Dec 20, 2007
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    You must update your SIM software with a model of the opamp you will use. Maybe you are simulating with the model of a lousy old 741 opamp that will not work in that circuit.
     
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