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Impedance vs frequency plot of input filter of SMPS?

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T

treez

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Hi,
How do I get the impedance vs frequency (fig 2.32a) plot of page 33 of the attached in LTspice?
https://www.vicorpower.com/documents/design_guides/DG-DCM-Design-Guide-VICOR.pdf

The LTspice sim is as attached, but I cannot make it work and cannot get fig2.32a
I can get the transfer function plot (fig 2.32b), but not fig2.32a.

I am just thinking that Impedance = v/i…..and so I am trying to divide the voltage at the output of the input filter, by the current coming out of the input filter, but it is not working.
I am taking 20log(10) v/i = x Db……and trying to work back to get v/i by doing v/i = 10^(xdB/20), but it doesn’t work.
Do you know how I can get fig2.32a?
 

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  • impedance vs frequency.TXT
    1.4 KB · Views: 40

Simulate the circuit in figure 2.31a with about 50mOhm for the inductor resistance. Plot voltage at I1 with the Y axis set for log instead of db.

Voltage at the current source is resistance when the AC current source is set for 1.
 

Surprising that the datasheet shows several filter circuits with impedance curve, but none is specifying the inductor series resistance.

Basic electric circuit knowledge clarifies however that you can't arrive at these curves without inductor series resistance (or respective external series resistance, whatever causes it).
 

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