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When I design with PI expert, in this case a 3W LNK363GN based PSU, the resulting schematic includes an input LC PIE filter on the rectified mains and a recirculating capacitor across the transformer isolation barrier. Is this sufficient for EMC? In the past I have found this to be the case but an inductive parts supplier is suggesting I add a CMR choke on the mains and load side. This would make the design quite complex and expensive. The input voltage range in this case is 85 to 250Vac and we need EN compliance.

Hi mquinlan,

You may find the following appnote useful:


In short, for designs <5W, the input LC pi filter is a valid alternative to solutions utilizing a common-mode choke. In the end, because EMI depends on so many factors including the PCB layout, magnetics, cabling, etc., it is still prudent to verify compliance for your particular solution.