Analytical calculation of conducted EMI in flyback converters

Flyback converter is widely used for its high efficiency. However due to fast switching currents and voltages, it can cause high conducted emissions in a system. In this paper we present a method to characterize the EMI noise generation and the coupling mechanism in flyback converters. We also derive analytical formulae to calculate the frequency and amplitude of this EMI noise, which provides an easy way to predict EMI noise in early design stage. The results calculated by formulae are compared with simulation and agree well. A new standard filter design procedure for flyback converter is proposed based on these analytical formulae, which can help to mitigate electromagnetic compatibility (EMC) risk in the beginning of the project.