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An Investigation of Electromagnetic Radiated Emissions from Wireless Charging System for Mobile Device Using Qi Standard

In this paper, the electromagnetic radiated emissions from 30 MHz to 1 GHz of a wireless charging system for a mobile device using Qi standard are investigated. It has been found that the common mode current on USB cable is the main cause of radiation and the noise source is the full bridge inverter in power transmitter. The common mode current path is highlighted to explain the radiation mechanism. The switch node voltage in time domain and frequency domain are measured for more understanding of noise source. A full wave simulation model is built to roughly estimate the far field radiation. Methods to reduce the radiated emissions are also discussed and demonstrated experimentally.