Practical characterization of EMI filters replacing CISPR 17 approximate worst case measurements

A common approach for selecting a suitable EMI filter is detailed based on the example of a realized single-phase 500W PFC rectifier. The presented work separates conducted EMI noise into Differential Mode (DM) and Common Mode (CM) components and derives expressions for the DM and CM insertion losses achieved if a given EMI filter is connected to a dedicated power converter. With the use of hardware measurement results it is shown that the impedances of the EMI filter and the PFC rectifier have a considerable impact on the realized insertion losses, which, at particular frequencies, may be even less than approximate worst-case estimations proposed in CISPR 17.