Switching Power Supplies A - Z

Practical EMI Line Filters

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Therefore, a) providing a good metal enclosure, and b) properly connecting it to

earth is the most effective method of preventing radiated EMI. However, by creating

this galvanic connection (to earth), we also now provide a “multi-lane freeway” for

the conducted (common mode) noise to flow “merrily” into the wiring of the

building. So now, to be able to stay within the applicable conducted emission limits,

we need to provide a common mode filter somewhere.

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Generally speaking, if the equipment is designed not to have any earth connection

at all (e.g. a two wire ac cord), there will usually be no metal enclosure present

either ...