Power Relay Module Based Charging Function Extension for Standard Wireless Charger

Owing to the merits such as higher convenience and safety, the inductive power transfer has been increasingly popular to wireless charging applications. The corresponding standards such as Qi further promote and guide the design of wireless chargers. However, a standardized transmitter usually fails to charge a device with mismatched size. This paper explores the power relay module to extend the charging function. Two coils in the relay module are utilized to rebuild an efficient power transfer path and address the size mismatch issue. The bottom relay coil efficiently absorbs power from transmitter through a strong coupling, and then transfers power to the top relay coil with wired connection. The top relay coil then excites a magnetic field and delivers power to the receiver. The two relay coils can be customized with the identical sizes of transmitter and receiver respectively, and significantly improve the power transfer efficiency. In the relay module, the high-order compensation network is applied to help to ensure the load-independent output voltage for the device. Finally, based on the proposed method, a 20 V/20 V 30-W prototype is built. The nearly constant output voltage and 88% peak efficiency are achieved.