Amplifier problem

Discussion in 'Homework Help' started by boks, Dec 17, 2008.

  1. boks

    Thread Starter Active Member

    Oct 10, 2008

    The op-amp is ideal, and I'm supposed to find V_{o,B}.

    I know that there is no current going in to any of the + and - terminals of an ideal op-amp. But can there be current going out from either of the two (or negative current in, if you want)?

    If not, I guess I can conclude that there is no current going through R_1 and R_2?
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Not if the op amp is ideal.
  3. Audioguru


    Dec 20, 2007
    Of course there is a current in the input R2 that equals the opposite phase current in the feedback R1.

    Vob is the input voltage times -R1/R2.

    The opamp would work a lot better when it is powered. Since its (+) input connects to ground then the power supply must be positive and negative.
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    Oops, I only considered the R1 & R2 on the non-inverting input. The others should be R3 & R4 for clarity.
  5. steveb

    Senior Member

    Jul 3, 2008
    I'm not sure if I'm understanding the responses correctly. Just for clarity, are we saying that the the OP (boks) is correct that there is no current flow in R1 and R2 connected to the noninverting input, but there is current for R1 and R2 on the inverting input.

    I believe this is the correct answer, but the responses don't seem to state this clearly.