Simple OPamps question

Discussion in 'General Electronics Chat' started by Crowbar, Jan 17, 2007.

  1. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    Good day. After carefull cheking of my cirquit I have founded one error: main power supply rails are +/-5v and when I adjusting offset at input of OPamop 5v is given. It can't be cause Opamp does not have rail-to-rails input. So to avoide this can I increase 5v rail to 7v rail- there I wiil have +7V rail and -5v rail power supply. So the question is: Am I right when thinking that this adjustment won't affect OPamp except its input voltage range (with +/-5 V supply have a +/-3V input; with +7v -5V supple have a 5v -3V input range)?

    Thanks for your help.
     
  2. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    Yes, that is correct. Depending on the output swing of the op-amp you can change power supply rails to help increase your output swing (headroom). Of course, the easiest way is to simply use a RRO op-amp.:cool:
     
  3. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
    32
    0
    Ok, but will output signal from OpAmplifier, which is powered from unequal rails, be still refered to common GND?

    The part of schematic where the problem is
    [​IMG]
     
  4. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    Of course they will share the same circuit common...they would have to (unless you are doing something weird).

    What are your voltages at pins 2 and ? 2.5V?
     
  5. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
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    0
    This crquit is used to have programmed +/-2,5V ouput. AD5220 is a digital potentometer and OpAmp+2 resistors are working as voltage follower with a 2,5V offset, which is given by 2,5v reference.
     
  6. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    If you only need a 2.5V reference from the op-amp, why not use a voltage follower rather than the 'complicated' circuitry you have?
     
  7. Crowbar

    Thread Starter Active Member

    Dec 19, 2006
    32
    0
    You misunderstood me: voltage is adjusted between +/- 2,5V
     
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