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I am confused regarding the working of a Line Impedance Stabilizer Network. To analyze the conducted EMI of my DC-DC converter (simulation only at this point of time) I know we need to connect in series a LISN device. The filter portion will come after the LISN module, before the converter. My question is, isn't the LISN itself acting like a filter? Because when I was simulating the converter I had first chosen the LISN inductor = 50 uH, and this caused trouble since it is a 12 V to 5 V buck converter. When I changed it to 5 or 10 uH, all the waveforms were as expected.

Also, how is the correct LISN chosen in the real world for a switching converter?

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    \$\begingroup\$ The EMC standard you're trying to meet should specify what LISN to use when testing conducted emissions for that standard. \$\endgroup\$
    – The Photon
    Dec 13, 2020 at 19:14
  • \$\begingroup\$ I thought the Wikipedia article's section on "Function of a[n] LISN" does a pretty good job of explaining what it is and does. And like The Photon said, the standard you have to comply to (e.g. IEC 60730-1) should define the LISN filter values. \$\endgroup\$ Dec 13, 2020 at 19:31
  • \$\begingroup\$ @ThePhoton I'm trying to abide by the CISPR 22 limits, and I think that sets the inductor value to 50uH. But when I use this in my circuit as you can see in the link in my post,this does not meet the expected waveforms at all, so I changed the L to a much smaller value like 5uH-10uH.What is to be done then? \$\endgroup\$
    – SM32
    Dec 14, 2020 at 4:41
  • \$\begingroup\$ If the LISN presents too high an impedance to your circuit, you may have to increase the input bulk capacitance to compesnate. I think this was mentioned in a comment on your previous question. \$\endgroup\$
    – The Photon
    Dec 14, 2020 at 5:15
  • \$\begingroup\$ The whole concern of conducted emissions is you don't want your circuit drawing periodic current through an external wire (as the wire would radiate). You want all the periodic components of current to circulate in your circuit only. Using 100's of uF of input capacitance is not out of line (but then of course you may need to do something to limit inrush current when the external supply is first connected or powered up). \$\endgroup\$
    – The Photon
    Dec 14, 2020 at 5:20

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Yes, the LISN can be thought to be a filter, but maybe it helps if it is not thought as a filter, but a mains wiring simulator that gives devices to be measured a specific reference impedance, so that all devices are measured in same standard environment for conducted emissions.

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  • \$\begingroup\$ *Mostly for “conducted” emissions. \$\endgroup\$
    – user69795
    Dec 13, 2020 at 21:33
  • \$\begingroup\$ @user69795 Thanks fixed. \$\endgroup\$
    – Justme
    Dec 13, 2020 at 21:42

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