Circuit with Voltage Amplifier

Discussion in 'Homework Help' started by epheterson, Feb 5, 2009.

  1. epheterson

    Thread Starter New Member

    Feb 5, 2009
    Here's the question, you don't need to read it all to help me out. I need to find R4.

    I'm given R1 = R3 = 10kOhms and Gain = 2.
    Using this, I find that R2 = 20 kOhms and using the forumula G=Vc/(V2-V1) with V2=[-5,5], I find that when V2 = 5V, V1 = 2.5V.

    So knowing all this, which is pretty much the entire circuit, how can I find R4? I think I have to convert the voltage amplifier into its voltage-source equivalent with a voltage of A.(V+-V_) where A. = infinity. It's this step that confuses me. Is it even necessary to do this?
  2. MasterSnow


    Jan 18, 2009
    It looks to me like it's as simple as solving for an expression that equates that output gain of the amplifier to the resistances of the circuit using node analysis. I think you can solve this in two equations. For this, just assume the op amp is ideal - no need to break it down into an equivalent circuit model.