A Self-Synchronized Maximum-Power-Point Inductively Coupled Wireless Battery Charger for Embedded Microsensors

Embedded microsensors are critical in today's fast-growing Internet of things, as they provide an interface between the physical and digital worlds. An inductively coupled power receiver can replenish the onboard batteries and extend the microsensor's lifetime. Among all power receivers, the switched resonant half-bridge receiver outputs the highest power, as it can operate beyond the circuit's breakdown adjust power transfer for maximum power point (MPP). However, switch synchronization and practical power transfer control remain two challenges. this article presents a self-synchronization technique and an MPP adjustment control scheme for the switched resonant half-bridge wireless charger. The charger senses the high oscillation voltage without limiting the breakdown. Moreover, it can adjust the energy transfer frequency to reach and stay at the MPP when coupling varies. A prototype wireless charger is fabricated with 180 nm CMOS technology. The prototype charger, operating at 110 kHz, receives a power up to 38 mm with a pair of 11.7 × 3.5 × 2.6 mm
³
coils. Measurements show the charger outputs up to 89% of the available power across a 0.067%-7.9% coupling range. The output power (in the percentage of available power) and coupling range are 1.3× and 13× higher than the comparable state-of-the-arts.