ANALYSIS OF ELECTROMAGNETIC INTERFERENCE RADIATIONS FROM THE PCB TRACES

This paper presents the analysis of Electromagnetic interference (EMI) radiations from the printed circuit boards (PCB) of SMPS (Switched Mode Power Supplies) and the results obtained can be used to choose the best trace lengths of PCB's to make it Electromagnetically Compatible. The emission range of frequencies are considered from 30 MHz to 1GHz. SMPS has advantages like good efficiency, light weight and can be used to improve input power factor, but it produces high frequency EMI noise. The SMPS has a power switch switching large voltages and currents at high frequencies usually above 100 kHz having low rise time, because of this there are high frequency conducted and radiated emission from their PCBs. Hence radiation from its PCB traces needs to be evaluated. These high frequency component currents causes EMI emissions. Several signals emit radiations from the printed circuit board. This PCB acted like an antenna. As per international standards the EMI emission from such SMPS are measured at a distance of 3 m. The emission are calculated and it was verified using CST software simulation tool. The results are in close agreement. From the results obtained it is inferred that by increasing the length of the PCB trace, the magnitude of the radiations will increase up to 500 MHz and beyond it there may be resonance occurring. The results can be used by PCB design and layout engineers to select the best trace length to reduce the EMI radiations from the PCB effectively.