Power Relay Module Based Multiple-load Charging Capability Extension

Due to the limited size, the existing Qi standard based wireless chargers are not attractive and even fail to charge multiple devices. This paper explores the passive power relay module to extend the multiple-load capability cost-effectively without modifying the original transmitter. A power relay module constructed with three layers is proposed to rebuild an efficient power transfer path. When it is inserted between the transmitter and receivers, the power will be extracted from the transmitter by the bottom-layer auxiliary relay coil, then delivered to the top-layer relay coil through wired connection, and finally picked up by the receivers. A middle magnetic shield layer is also adopted to simplify the mutual coupling relations. The equivalent circuit model of the proposed system configuration is given based on fundamental harmonic approximation, and further to analyze the voltage gain and power transfer efficiency. Finally, a prototype system is built and measured under various load conditions. The almost load-independent output voltage is achieved, and the peak efficiency reaches 87%.