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LOW PASS FILTER (LC) resonanting.

Discussion in 'Misc Electronics' started by [email protected], Oct 28, 2013.

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    I am looking to design a low pass filter that has a cutoff frequency of 20 kHz. The filter needs to be able to handle about 20A of current so the direction I have taken is an LC filter. (Inductor with a high current rating).

    I simulated the low pass filter tonight (LTspice) using the values of 7.9 uH and 15 uF suggested from some of the online lowpass filter calculators.

    From the simulation I see 0 dB in most of the passband but then I see a huge resonance point of +32 dB at 14.49 kHz!

    Here is a link to the simulation result:

    1.) Is there a way to eliminate this resonance?

    2.) Is there a different filter that would have less peaking but still ableto handle the high current for this application (20A)?

    3.) There is an H-brige that will be modulated at 200 kHz (pwm) and this will going through the 20kHz lowpass filter to given a DC voltage without allthe pulses. If the resonance point is kept as it is what type of issues would this cause? Is this even a problem?

    4.) From the simulation I see a cutoff frequency of 22.7 kHz instead of 20 kHz. What is the best way to tune this? Maybe to keep the capacitor fixed (15 uF) and then sweep the inductance value in simulation?

    Thank you you so much for your thoughts.

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