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Second order circuit need some confirmation on the steps involved.

  1. Mar 10, 2013 #1
    1. The problem statement, all variables and given/known data
    Find v(t) for all t>0. Use second order method.


    2. Relevant equations



    3. The attempt at a solution
    Before the switch is closed:
    solving for i:
    -80+160i+80i+80i=0
    i=0.25A

    KCL:
    From node v(t):
    [C dv(t)/dt] + i(t) + [V(t)/4] + [(v(t)-80i)/80]+[(v(t)-80)/160] = 0

    KVL:
    v(t)=L di(t)/dt

    Later on solve the 1st equation for i(t), then substitute into KVL equation.
     

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  3. Mar 10, 2013 #2

    gneill

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    Staff: Mentor

    Consider replacing everything before the switch with a Norton equivalent.

    Have you learned about Laplace transforms yet?
     
  4. Mar 10, 2013 #3
    yes, but the question ask us to use 2nd order to solve it.
    Do we need to take in account for the dependent source?
    we convert it to 80*0.25=20V
     
  5. Mar 10, 2013 #4

    gneill

    User Avatar

    Staff: Mentor

    In my opinion, I don't think that using Laplace transforms to solve the differential equation would be cheating...
    Yes, the dependent source makes a difference, but you may be surprised by the resulting Norton equivalent. The Norton equivalent should have a current source in parallel with a resistance; 20V is not a current (nor is the the correct Thevenin voltage).
     
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