About Analysis of Emissions from a Switched Mode Power Supply

The paper is dedicated to the analysis in the frequency domain of the currents (in common mode and differential mode) which generate conducted emissions in the supplying cable of the equipment containing a switch mode power supply (SMPS). The performed simulation considers the standard CISPR 16-1-2 which refers to specifications, methods, and test apparatus for the measurements of disturbances and immunity to conducted emissions. One proposes solutions to limit and control the conducted emissions generated by the SMPS within the supplying cable that result into noise currents and high frequency currents within the range 150 kHz – 30 MHz that might interfere with other electric equipment. Various ways to limit the mentioned emissions are simulated and analyzed. The influence of the duty-cycle over the frequency spectrum from the conducted emissions range is considered and the worst case is determined. The conclusion is that the optimum filtering solution involves the use of an EMI filter, the results being compared to the CISPR 22 standard.