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virtual ground of OPA

Discussion in 'Homework Help' started by nick, May 7, 2004.

  1. nick

    Thread Starter New Member

    May 7, 2004
    1
    0
    Is there anyone who knows why "virtual ground" does not exist when there is no negative feedfack in the OPA circuit?
    I also saw some OPA circuits that have both positive/negative feedback, how can I know if the "virtual ground" still good or not?
    THANKS FOR HELPING
     
  2. Mjollnir

    Member

    Apr 22, 2004
    27
    0
    basically when u have negative feedback, the output drives the potential between the two terminals to 0, hence the virtual ground/short..

    if u have postive feedback, it will saturate @ the supply limits, and no feedback u dunno the answer unless u know the exact gain (which can vary greatly from device to device)

    Hence u always use negative feedback to get the desired gain..

    and u can have postive and negative feedback together, and u wont get saturation as long the magnitude of the negative feedback is bigger than the positive...
     
  3. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    you said you some circuits using OPAs having both negative and positive feedback. are we talking about integrators or active filters or neutralizing input capacitance to optimize response time or a free running multivibrator or wave generator or pulse width modulator. all of these employ both feedback type.
     
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