A 6.78MHz Wireless Power Transfer System With Efficient Global Hysteresis Control for Implantable Medical Devices

This paper presents an efficient global hysteresis control for output voltage regulation in order to improve the overall system efficiency. Compared with the conventional regulating-rectifying schemes in receiver, the proposed method achieves high light-load end-to-end (E2E) efficiency by shutting down the transmitter (TX) during freewheeling operation period of the rectifier. In addition, a carrier-less pulse-resonant-current modulation technique is proposed to efficiently wake up TX in time. Besides, the residual power of the TX coil in shutdown phase is recycled to further enhance the efficiency. This proposed wireless power transfer system is designed in a 0.18µm BCD process, and regulates an output voltage of 3V. Simulation results show that the maximum output power is 450mW with a high light-load E2E efficiency of 55.9%. The efficiency improvement reached 27.6% compared with the RX regulation only. For a load switching between 15mA and 150mA, the transient response is less than 100ns.