+Vin and -Vin

Discussion in 'General Electronics Chat' started by new2circuits, Apr 23, 2009.

  1. new2circuits

    Thread Starter Member

    Apr 22, 2009
    21
    0
    HI: Can someone explain the whole +Vin and -Vin concept as it relates to a differential input to an op amp for instance or any device that accepts a dual supply?
    Thanks
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    If an opamp or comparator has a positive and negative supply then the input and the output can be at 0VDC and the signal will swing positive and negative without coupling capacitors.
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    A differential input circuit is one that actively responds to the difference between two terminals rather than the difference between one terminal and ground.

    The +Vin and -Vin are defined as the differential inputs of the op amp. The output of an op amp is the gain, A, multiplied by the difference of +Vin and -Vin.

    Output = A * ((+Vin) - (-Vin))

    In the case of an op amp the gain A is usually very high and therefore feedback is placed around the op amp to control it.

    The differential inputs are independent of whether or not the device accepts a dual supply. The idea of dual supply is explained in #2 by Audioguru.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I read the question too fast.
     
  5. new2circuits

    Thread Starter Member

    Apr 22, 2009
    21
    0
    Thanks to both of you for your response. I appreciate it.

    Looks like I need to go back to basics and understand the concept of dual supply and +Vin -Vin a bit more. I studied ee a long time ago, but never really used it until now. I'm finding it difficult to come back up to speed, so I appreciate you getting me there via your answers. Thanks
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Ground can also be a designated reference point, as long as it is low impedance (ie, high current).
     
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