Non inverting amplifier gain

Discussion in 'General Electronics Chat' started by Joshmikal, Sep 26, 2013.

  1. Joshmikal

    Thread Starter New Member

    Sep 26, 2013
    The gain on a Non inverting amplifier is 1 + r2/r1
    Vout = vin(1+r2/r1)
    I'm wondering what the gain will be if r1 is not grounded and is instead connected to v1. Will the gain then be vout=(vin-v1)(1+r2/r1)?
    Thanks for your help guys!
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    An opamp will always try to make the sum of the inputs equal to zero. So to tackle this problem use the superposition theorem.
    Edit: If you are not student but a self-taught hobbyist I may offer some more help
    Last edited: Sep 26, 2013
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    I would think...

    Vo=(1+R2/R1)*Vi - (R2/R1)*V1
  4. w2aew

    Active Member

    Jan 3, 2012
    For what it's worth - here's a video that shows a more practical way to think about op amp operation. This approach seems to help many people visualize what an op amp circuit is doing (and what it will do).
  5. LvW

    Active Member

    Jun 13, 2013
    Yes - and in case Vi=V1 we have a unity gain amplifier - independent on the resistor ratio.
    This is a very special circuit that can be used for unity gain operation of an uncompensated operational amplifier.
    In this case the feedback factor (that means: the loop gain) can be adjusted for stable operation - independent on the closed loop gain (that always is unity).
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I can make a reasonable guess as to what you mean by Vout, vin, and r1 and r2.

    I have no idea what you could possible mean by v1.

    A proper schematic with reference points is required.
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    Presumably V1 is simply another potential within the common mode range. When V1 is zero volts one has the classic non-inverting amplifier with gain.