Switching Power Supplies A - Z

Chapter 9

Figure 9-5: A CM and DM Separator

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Both methods above unfortunately require modifications to the standard LISN —

because they invoke a certain simultaneous math between the V

L

and V

N

components. However, a LISN normally provides either V

L

or V

N

at any given

moment — not both (at the same time, as required here). We can modify the

traditional LISN, but that is not only tricky to do, but also hazardous because of the

high voltages involved. Therefore, a completely different approach is simply to buy a

LISN explicitly designed for the purpose of providing separate CM and DM noise

scans (besides providing the necessary “summed up” scan for achieving ...