1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

CIRCUIT ANALYSIS: 8 Resistors, 1 IVS, 1 Differential Op-Amp - Find Vo

  1. Feb 5, 2007 #1
    1. The problem statement, all variables and given/known data

    The circuit below is a differential amplifier driven by a bridge, find [itex]V_0[/itex].

    [​IMG]


    2. Relevant equations

    KCL, v = i R, Ideal Op-Amp relationships


    3. The attempt at a solution

    I added 4 voltage markers.

    [​IMG]

    By the Ideal Op-Amp relationships, we know that there is 0 current at both input terminals of the Op-Amp.

    KCL at [itex]V_2[/itex])

    [tex]\frac{0.005\,-\,V_2}{40000}\,=\,\frac{V_2}{60000}\,+\,\frac{V_2\,-\,V_4}{20000}[/tex]

    [tex]18\,V_2\,-\,12\,V_4\,=\,0.003[/tex] < ------ Equation 1

    KCL at [itex]V_4[/itex])

    [tex]\frac{V_2\,-\,V_4}{20000}\,=\,\frac{V_4}{80000}[/tex]

    [tex]4\,V_2\,-\,5\,V_4\,=\,0[/tex] <----- Equation 2

    Now, using equations 1 and 2, I get [itex]V_2\,=\,0.003571\,V[/itex] and [itex]V_4\,=\,0.002857\,V[/itex]. Does that seem right?

    By the relationships of an ideal Op-Amp, [itex]V_3\,=\,V_4[/itex], so [itex]V_3\,=\,0.002857\,V[/itex].

    KCL at [itex]V_1[/itex])

    [tex]\frac{0.005\,-\,V_1}{10000}\,=\,\frac{V_1}{30000}\,+\,\frac{V_1\,-\,V_3}{20000}[/tex]

    [tex]11\,V_1\,-\,3\,V_3\,=\,0.03[/tex] <----- Equation 3

    KCL at [itex]V_3[/itex])

    [tex]\frac{V-1\,-\,V_3}{20000}\,=\,\frac{V_3\,-\,V_0}{80000}[/tex]

    [tex]4\,V_1\,-\,3\,V_3\,+\,V_0\,=\,0[/tex] <----- Equation 4

    Using equations 3 and 4, I get [itex]V_0\,=\,0.004363\,V[/itex].

    [tex]V_0\,=\,4.363\,mV[/tex] <------ Is that right?
     
    Last edited: Feb 5, 2007
  2. jcsd
  3. Feb 5, 2007 #2
    Bump - Bump:)
     
  4. Feb 5, 2007 #3
    Looks good. Quick question though, why don't you use linear algebra instead of messy substitutions?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: CIRCUIT ANALYSIS: 8 Resistors, 1 IVS, 1 Differential Op-Amp - Find Vo
Loading...