Summing/Differential? Amplifier

Discussion in 'General Electronics Chat' started by Axel, Nov 2, 2008.

  1. Axel

    Thread Starter New Member

    Nov 2, 2008
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    0
    I have a question that OpAmp looks like Summing but there are Voltage applied to the + input.

    note that there are 2 input voltage 150mV and -153mV to the 741 OpAmp, i know the calculation of Summing Amplifier and the value shud be 0.28V, but when connect a 0.5V to the + input, it bcome looks like differential but without Rf and Ri, and the output become 3.188V, can someone show me the formula for getting 3.188V?
     
    Last edited: Nov 2, 2008
  2. hgmjr

    Moderator

    Jan 28, 2005
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    The gain of the opamp for signals applied to the + input is 5.8. When you mulitply 0.5 times 5.8 you get 2.9V. The balance of the output signal is accounted for by the other two voltage inputs and their associated gains.

    In summary, the simulated opamp is operating correctly.

    hgmjr
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you make the analysis of the circuit you get this equation:

    Vo=(-V1+0.5)*R5/R6+(-V2+0.5)*R5/R3+0.5

    Plug the numbers in and you get the answer the simulation gave you.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    The above equation is the same as mik3 using the LaTex format.

    hgmjr
     
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