Impedance of a parallel rc circuit

Discussion in 'General Electronics Chat' started by ryanmoser, Nov 5, 2015.

  1. ryanmoser

    Thread Starter New Member

    Nov 5, 2015
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    1. If a circuit consisted of a resistor R parallel with a capacitor C is given an external current excitation with frequency of ω, let the current equals to I0*exp(jωt), what is the response of voltage E? Would the impedance equals to R(1-ωCRj)/(1+ω^2*C^2*R^2), the same as the case when the circuit is excited by AC voltage E0*exp(jωt)?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,014
    3,234
    The impedance of a parallel RC circuit is inversely proportional to frequency.
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
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    there is no resonant point for rc circuits like there is on lc circuits. the impedance, actually reactance, changes with frequency in a fairly linear manner.
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
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    I seem to remember something about phase angle and ELI the ICE man coming into play. Something about a vector???
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    eli the ice man is for lcr circuits. phase lead and lag with capacitive and inductive circuits. for rc, its just a ratio of capaccitive reactance and resistance gives phase shift.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
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    My post (#4) was intended to be a hint to the OP. Please correct me if I'm wrong, but when calculating effective impedance, isn't the answer a vector value of Xc and R? It has been a long time since exposure to those details.
     
  7. ryanmoser

    Thread Starter New Member

    Nov 5, 2015
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    20151106184554.jpg
    The attached figure shows how I derive the response of voltage with regard to a AC current signal. However, additional term (RED) is found in the expression of E? Where is wrong?
     
  8. jjw

    Member

    Dec 24, 2013
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    Do you really need to derive these equations or can you just use known impedances of R and C and then the parallel impedance of these ?

    The term I0/(s-jw) must be wrong.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    It took some digging, but I found support to what I seemed to have remembered from so long ago....

    You probably don't have a navigation computer, but a calculator will work.
     
  10. ryanmoser

    Thread Starter New Member

    Nov 5, 2015
    3
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    Thank you
     
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