Singe Supply opamp in LTspice?

Discussion in 'General Electronics Chat' started by nemuikuma, Apr 5, 2012.

  1. nemuikuma

    Thread Starter New Member

    Apr 4, 2012
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    Hi!
    I'm trying to simulate Single supply opamp with LTspice with no luck at all. (9 volts)
    It behaves normally with split supply, so presume the problem is not with the circuit.
    The only way it seems to function is if i referenced the feedback resistor to 4.5 and not to ground) and a give the biasing from the AC source.
    If i try to bias with a voltage divider from the 9 volt source it does not work, i have the same 4.5 volt DC on the input but it doesn't work anymore it gives me about -40db to -70db ac response and about 7.2 volt DC on the output and i also get this if i reference the feedback resistor to ground

    Anyone know why is this or how to make split supply opamp circuits?
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I have never had a problem with this. Attach the schematic that is causing problems. You can also attach the .asc file.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    I suspect a problem with a ground connection. Do you have the power supply grounded? It must be for proper operation in the single supply mode.
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Good point. I believe LTspice will give erroneous results on any simulation that does not include a ground symbol.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    With the feedback resistor "referenced to ground" instead of capacitor-coupled to ground then the opamp is simply amplifying the 4.5V reference voltage on the (+) input. Then the output is saturated high at +7.2VDC.
     
  6. nemuikuma

    Thread Starter New Member

    Apr 4, 2012
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    Thank you, that was the problem !
     
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