EMI Reduction of a Soft-switched High Step-down Converter Using Passive Compensation Method

In this paper, an EMI reduction method is applied to a new high step-down converter which has a coupled inductor, a synchronous rectifier and method with an auxiliary soft-switching cell. The freewheeling diode is replaced with a synchronous rectifier (SR) and zero-voltage-transition (ZVT) condition is provided for the main and SR switches. The auxiliary switch acts under zero-current switching. To reduce conducted electromagnetic emissions, a passive method is utilized by adding another winding on the core of converter coupled inductor to compensate the common-mode noise current generated by the parasitic capacitor of the main switch. The operating modes and theoretical waveforms are presented and simulation results of a 100W-l00 kHz converter are shown to verify the theoretical analysis. The conducted EMI predictions confirm the benefit of the passive compensation method.