Expression for op-amp circuit

Discussion in 'Homework Help' started by ADCapacitor, Mar 22, 2016.

  1. ADCapacitor

    Thread Starter Member

    Feb 3, 2016
    38
    0
    The expression of Vout=-Vin1+Vin2+Vin3

    I apply the virtual short condition
    V+=V-
    i1=(V+ - Vout)/R
    Vout=R*i1 + V+
    Vout=(V+ - Vout)+V+
    =2V+ - Vout

    It seems the voltage divider cannot be applied for V+
    How can I find the V+ in this circuit?
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Try to use superposition principal .
     
  3. MrAl

    Well-Known Member

    Jun 17, 2014
    2,438
    492
    Hi,

    In short, if you want to derive an expression to show the relationship between three inputs and one output, then you have to at least include those three inputs in the expression. That means Vin1, Vin2, and Vin3 have to be somewhere in the expression too.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,748
    4,796
    Go back and learn where the voltage divider equation comes from. Then use that same approach to find V+.
     
Loading...