EMI-Filter Interactions in a Buck Converter

The paper investigates the effects of EMI filter in the dynamics of a buck converter. It is shown theoretically that the EMI filter may increase significantly the load sensitivity of the voltage-mode-controlled converter but the peak-current-mode-controlled converter is quite insensitive to the EMI filter interactions. Experimental validations are carried out using a buck converter under three different control modes - voltage-mode, peak-current-mode and output-current-feedforward peak-current-mode control. The investigations show that the phenomenon causing the instability under peak-current-mode control is the negative-resistor-oscillation (NRO) phenomenon, and confirm also the excess EMI-filter sensitivity of the voltage-mode controlled converter.