Design of a 5-W power receiver for 6.78 MHz resonant wireless power transfer system with power supply switching circuit

A 6.78 MHz resonant wireless power transfer (WPT) system with a 5 W fully integrated power receiver is presented. A conventional low-dropout (LDO) linear regulator supplies power for operating the circuit in the power receiver. However, as the required operating current increases, the power consumption of the LDO regulator increases, which degrades the power efficiency. In order to increase the power efficiency of the receiver, this work proposes a power supply switching circuit (PSSC). When operation starts, the PSSC changes the power source from the low-efficiency LDO regulator to the high-efficiency step-down DC-DC converter. The LDO regulator operates only for initialization. This chip has been fabricated using 0.18 μm high-voltage bipolar- CMOS-DMOS (double-diffused metal-oxide-semiconductor) (BCD) technology with a die area of 2.5 mm x 2.5 mm. A maximum power transfer efficiency of 81% is measured.