Common-Mode EMI Behavior of an IGBT Buck Converter

The common-mode electromagnetic interference(CM EMI) of Buck converters is analyzed in detail in or-der to get the relationship between the CM EMI and key operation parameters.A CM equivalent circuit of the con-verter is proposed,and the relationship between spectrum of the CM noise source and operation parameters such as input voltage,switching frequency,switching speed are analyzed.To verify and supplement the theoretical analysis,experiments are carried out on an IGBT Buck converter to test the actual influences of input voltage,switching fre-quency,duty ratio,load current and driving resistance on the CM EMI.The results indicate that CM EMI is not af-fected by the duty ratio and it is proportional to the input voltage and switching frequency.Both the load current and gate drive resistance can influence the CM EMI since they can change the switching speed.The influence of load cur-rent is closely related to characteristics of switching devices.