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Question Regarding Operational Amps

  1. May 31, 2012 #1
    Hello ,

    i would to ask if it is possible for an INVERTING summing amplifier of three input voltages ( V1,V2,V3) to have some of them negative and some positive i.e V1>0 and V2<0 and V3<0 or any other combination.

    Thank you !
  2. jcsd
  3. May 31, 2012 #2


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    Staff: Mentor

    That should be okay, as long as the opamp is running from split power supplies (like +/-12V), and the input voltages sum to a value that is within the input voltage range of the opamp.
  4. Jun 1, 2012 #3
    Thank you :)
  5. Jun 1, 2012 #4


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    Science Advisor
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    Most voltage summing amps are 'really' summing currents through high resistances at a 'virtual earth' so it may not matter that some of the voltage contributions are negative when the PSU is only positive and earth, as long as the sum of currents is greater than zero. That's just the equivalent of current biasing the input appropriately and getting yourself a level shift, effectively.
  6. Jun 1, 2012 #5
    In principle you can have as many input (+/-) voltages as you like as long as their result is within the operating parameters of the op amp.....power supply etc
  7. Jun 1, 2012 #6


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    Science Advisor
    Gold Member

    Yes - that's a good way of putting it.
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