+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

    Distinguished Member

    Sep 25, 2008
    948
    52
    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
    20,870
    2,649
    Ground can also be a designated reference point, as long as it is low impedance (ie, high current).
     
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