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I am designing a π-type LC filter with a frequency cutoff of approximately 1khz. Simulating the filter in LTspice gives the following Bode plot. It starts dropping off at ~100hz before dropping significantly, however, I do not know why the filter 'bounces' at the 5khz mark before dropping again.

Why does the simulation show a 'bounce'? Additionally, what is the purpose of the dotted line?

Ferrite bead is a WE 7427503-UKL-40060, capacitors are standard aluminium electrolytics.

enter image description here

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The dotted line is the phase angle. The scale for it is on the right and if you right click on the scale it will give you the option to not display that trace.

A ferrite bead is not going to give you a response like an inductor, they act like a combination of inductances, capacitances snd resistances so you’ll get resonances like the one at around 6 kHz and attenuations you might not expect. If you want a filter with a nice predictable response curve use an inductor, a ferrite bead has a different purpose.

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  • \$\begingroup\$ If you right-click on the ferrite bead, you will get a list of the bead properties showing Inductance, Series Resistance, Parallel Capacitance, and some other parameters. The parasitic components, in conjunction with the circuit elements, will cause the behaviour you are seeing. \$\endgroup\$
    – qrk
    Commented Mar 5 at 15:27
  • \$\begingroup\$ would the 'bounce' negatively impact the reliability considering it is used in a high-power application(24V, 3A)? \$\endgroup\$
    – lemon
    Commented Mar 6 at 20:01

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