An integrated multimode battery charger in a Qi compliant wireless power receiver

In this paper, an integrated multimode battery charger in a Qi-compliant wireless power receiver is presented. The proposed wireless battery charger includes a synchronous rectifier circuit and a multi feedback low dropout regulator. The charging circuit automatically switches trickle current, constant-current, and constant-voltage mode corresponding to battery voltage. Through control of the target rectified voltage from the perspective of the wireless power receiver, the synchronous rectifier circuit can generate an adaptive rectified voltage to closely track the battery voltage, which significantly reduce the power loss in the charging circuit. The wireless battery charger was implemented with a TSMC 0.18 µm BCD 1P5M process and the experimental results show the charging current of constant-current mode is 1 A and the final voltage of the wireless battery charger is 4.2 V. The maximum efficiency of the overall system is 78%.