DM EMI Reduction using the Gate Drive Signal in a Flyback Converter

With the miniaturization and high frequency of integrated circuits, the electromagnetic interference (EMI) which could be divided into conducted interference and radiated interference has received more and more attention. It is well-known that the conducted interference depends on common-mode current and differential-mode current flowing through the parasitic capacitance of transistors and diodes in the power circuits. In order to present the conducted noise from interfering with other systems, this paper analyses the generation principle of noise current flowing the parasitic capacitance of transistor, and introduces a new active cancellation structure which is composed by a comparator and a RC differential circuit to suppress the noise current. The active cancellation structure designed in this paper uses a simpler structure to make the differential mode conducted EMI on the power line reach a lower level. This new method is also applied to the flyback converter with the simulation result that the conducted EMI is reduced obviously.