Study on EMI Characteristics of the Superjunction DMOS in Flyback Converter System

A new study on the relation between the electromagnetic interference (EMI) in the flyback converter system and the used superjunction (SJ) DMOS characteristics is proposed in this paper. In comparison to increasing the gate driving resistance (RG) or the gate-source capacitance (C
_GS
), it is found that the EMI noise can also be mitigated by reducing the ratio of the oxide part of the feedback capacitance (C
_GD,OX
) and the C
_GS
. The theoretical derivation and numerous simulations are presented to prove the aforementioned conclusion. In addition, the measurement shows that the peak EMI noise can be reduced by about 10 dBm when the C
_GD,OX
is reduced from 1.8 to 1.24 nF while keeping the CGS 2.3 nF in the experimental SJ-DMOSFETs. This paper has significant meaning for the design of SJ-DMOS to improve the EMI characteristic in the flyback system.