Conducted EMC modeling for accreditation in DC-DC converters

A practical lumped element method to model conducted emissions in a step-down DC-DC converter up to 100 MHz is presented. The higher frequency was chosen to enable radiated emission problems due to high switching frequencies to be identified using a relative easier conducted measurement setup. The model and measurements were based on MIL-STD-461F method for conducted emissions, which calls for conducted tests to be performed on a copper sheet earth plane. Much emphasis was placed on the accurate modeling of critical EMC components, the power inductor, the input and output capacitors and the so often neglected feed line running from the LISN to the converter. The impedances of these components were measured in two distinct methods, the lower frequencies with a constructed impedance measurement system of which the technique is outlined and the higher frequencies with a network analyser converting scattering parameters to Z-parameters. Based on these measurements, lumped element models were created and thus closely matching the measured results. These models were combined, together with the rest of the components in the converter that was implemented with model data collected from datasheets, so as to create a complete conducted emission model simulating accreditation measurements, creating confidence that the converter will pass EMC qualification.