This work presents a reconfigurable 6.78 MHz Class-E wireless power transceiver capable of delivering up to 45 W output power for device-to-device (D2D) fast charging. On the TX side, an adaptive impedance-matching technique maintains the Class-E PA in ideal zero-voltage switching (ZVS) and zero-voltage-derivative switching (ZVDS) operation under varying RX-side loading conditions. In practical WPT operation, the TX load impedance changes with RX battery voltage, temperature, and coil distance, causing the Class-E PA to deviate from its optimal switching condition, leading to hard switching or reverse conduction and significant drops in system power and efficiency.
The proposed adaptive control dynamically adjusts both the equivalent resonant capacitance and the Class-E switch bypass capacitor to compensate for load impedance variations in real time. When reconfigured as an RX, the transceiver reuses the TX-side bypass-capacitor control method to perform maximum power point tracking (MPPT), achieving further power enhancement without additional hardware overhead.Fabricated in a TSMC 0.18 μm BCD process, the proposed system achieves a peak output power of 45 W
in D2D applications, with a total efficiency of 68% and TX efficiency of 93%.