CLC filter transfer function help

Discussion in 'General Electronics Chat' started by paultwang, Apr 1, 2006.

  1. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
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    What is the transfer function of this filter? Does this filter have a name?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    1,723
    It is called a pi-filter because it has a vague resemblance to the greek letter pi.
    Depending on the transfer function and the location of the poles it may have other characteristics. I would expect it to have a lowpass characteristic.
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    Greeting paultwang,

    See attached PDF for the results of my analysis of your pi-network.

    I took great pains to micro-step through the derivation to insure that the movement from equation n to n+1 was clear.

    Hopefully someone will vet my effort and let me know if I missed the mark.

    hgmjr
     
  4. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
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    Thank you so much. I didn't expect it to become this complicated.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    You are very welcome.

    Transfer function calculations can be challenging but this one was was fairly manageable. It probably appears more complicated than it is because I tried not to take too large a leap between the intermediate equations so as not to throw the reader off.

    I was hoping someone would check my results to make sure that I did not drop a stitch in one of the many equations that I used to show my work.

    hgmjr
     
  6. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
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    Plotted using your equation.

    [​IMG]
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    I like it. Great Job......

    The plot looks just as I expected. It is a third order low pass filter just as papabravo had stated at the outset.

    The plot shows the -6 dB attenuation that you would expect when the two resistors are set equal.

    Can you expand the plot to show the slope at the point it takes a dive?

    hgmjr
     
  8. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
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    Couldn't upload png files.. Forum glitch.. blank page. Worked around.
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    hgmjr,

    Here's a plot from 1k to 1M,
     
  10. paultwang

    Thread Starter Well-Known Member

    Mar 8, 2006
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    Drew straight lines and found the corner frequency:
    [​IMG]


    Mathematically solved the -3dB and -6dB frequencies:
    [​IMG]
     
  11. leelsuc

    New Member

    Oct 16, 2009
    3
    0
    check following:

    fcutoff = 1/ (2*pi*sqrt(C*(L/2)))
    damping factor varies with input/output resistance.

    Electromagnetic compatibility handbook

    By Kenneth L. Kaiser
     
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