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Issues with nulling offset voltage

Discussion in 'General Electronics Discussion' started by rizvi, Jan 19, 2018.

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  1. rizvi

    rizvi

    13
    0
    Oct 27, 2017
    hello dears..

    i am trying to analyse op07d which is an ic for an operational amplifier. when i apply a biasing voltage of ±12 volts, ground both the input terminals, i get an output of 10.5 volts which is an offset but prety huge. as the data sheet suggests this value to be in microvolts. kindly help me out here. what i am doing wrong.
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    The input offset is the offset at the inputs, not the output. Without feedback, that offset will be multiplied by the gain of the op amp, typically 100,000 to 100,000,000. In your example, the small offset voltage is being multiplied by the gain and the op amp is trying to output a voltage higher than it can, so it is going as high as it can go, which is 1.5V below the positive rail.

    Once you add feedback to control the gain, the offset at the output will be much smaller.

    Bob
     
  3. rizvi

    rizvi

    13
    0
    Oct 27, 2017
    i tried using 4.7k resistors for both R1 and R2 making a gain of 1. and then i grounded both the inputs , still i was getting similiar results. i.e offset was trying to reach saturation.
     
  4. hevans1944

    hevans1944 Hop - AC8NS

    4,615
    2,154
    Jun 21, 2012
    R1? R2? A gain of 1? Grounded both the inputs? What inputs? Post a schematic with parts labeled for identification during subsequent discussions: identify R1 and R2 on the schematic and post a value next to each label.
     
  5. rizvi

    rizvi

    13
    0
    Oct 27, 2017
    i will keep that take care of that in future @hevans1944
    and thankyou bob. your point here led me to find my error.
    thankyou all
    '
     
  6. Aftabalam

    Aftabalam

    4
    0
    Mar 3, 2019
    You should have to use some other op-amp IC's(other than Op-07) those who are having minimum offset voltage.T here are so many IC's available in the market. If you have issues of offset causing error in your result you should initially choose op-amp Ic tHe one having least offset.
     
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