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OpAmp Gain trouble

Discussion in 'Electronic Basics' started by bunny, Dec 1, 2005.

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  1. bunny

    bunny Guest

    I am using the below schematic for a OpAmp TLC272CP. According to the
    formula of G = (R1/R2) the gain on this circuit should only be a matter
    of 11. however as you can see below it's closer to 15/16. I'm
    wondering what could cause this anomoly. I have put the circuit
    below(sorry for the Ascii) and what i put into the + of the opamp and
    what i got as output.

    Thanks



    base=2.0mv
    output=33.4mV


    +9V +9V
    | (+). |
    100k pot<------|\|
    | (-)| \_____.__R3____Meter__.
    | .-| / | |
    | | |/| | |
    | | | | |
    | .------R2-' |
    | | | |
    | R1 | |
    | | | |
    Gnd Gnd Gnd Gnd

    R1 = 1k
    R2 = 10k
    R3 = 10k
     
  2. Andrew Holme

    Andrew Holme Guest

    G = (R1+R2)/R1 = 11

    According to the datasheet, that op-amp has a 1mV typical input offset
    voltage.

    Try a larger input voltage e.g. 20mV or 200mV.
     
  3. Pooh Bear

    Pooh Bear Guest

    answered in s.e.d.

    Such questions should be cross-posted to avoid stupid duplication and waste
    of time.

    Graham
     
  4. Bob Monsen

    Bob Monsen Guest

    Get rid of R3.

    Also, try making a few measurements, and plotting the output vs input for
    input = .5, .4, .3, .2, .1... That might give you a clue as to what is
    happening.

    ---
    Regards,
    Bob Monsen

    Music is the pleasure the human soul experiences from counting without
    being aware that it is counting.
    - Gottfried Leibniz
     
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