Analysis of EMC characteristics of DC-DC regulators with different power conversion methods

On-board DC-DC converters are intended for providing various voltages for unique local consumption. Normally, these converters use readily available voltage distributed through the system or board, and the output voltage can be either higher or lower than the input bus voltage. This paper concentrates on the applications where the output requirements are for reasonably high current, lower voltage loads. Most suitable for that kind of application is the so-called “buck” type of switching regulator, where the input power is processed to obtain a train of pulses. The output voltage is derived from integrating the input power in an LC network. This paper is based on the analysis of a typical DC-DC “buck” converter with features strongly dependent on the line/load conditions. The affect of the control algorithm, various input line/load conditions and rise/fall time of the switching waveform on the EMC spectrum of the input noise generated by the converter is analyzed. The spectrum of the input ripple noise at different filtering conditions is compared to derive recommendations for a circuit board designer. The results of the experiments are applicable to any type of conversion topology of a DC-DC converter using pulsed input current