Determining Far-Field EMI From Near-Field Coupling of a Power Converter

The highly frequent switching of semiconductor devices in power converters is often the source of significant conducted and radiated electromagnetic interference (EMI). In order to understand how radiated EMI is emitted from the noise source, this paper first analyzes the generation of EMI currents of a power converter, and then explains that the far-field radiated EMI emission of a power converter is due to the radiation of common-mode current on attached cables, which is driven by the electric near-field coupling between the printed circuit board and the attached cables of the converter. Based on this idea, an estimate model of the far-field radiated EMI emission of a power converter is developed. By using transverse electromagnetic cell measurements and full-wave numerical calculations, the far-field radiated EMI emissions of a buck converter with different cable lengths are estimated. The estimated results are compared with the measured results from 3-m semianechoic chamber tests with the buck converter, confirming the validity of the model.