15.3 A 100W and 91% GaN-Based Class-E Wireless-Power-Transfer Transmitter with Differential-Impedance-Matching Control for Charging Multiple Devices

Having multiple devices charged by a wireless-power-transfer (WPT) system has become more common as illustrated in Fig. 15.3.1. A wide-power-range (no load $\sim 100\mathrm {W})$, compact, and efficient WPT system needs to include the following features. First, an impedance-matching technique that achieves zero-voltage switching (ZVS) and zero voltage-derivative switching (ZVDS) on a Gallium Nitride (GaN) switch is needed to reduce the efficiency loss caused by hard switching (HS) and reverse conduction (RC). Second, under high-power conditions, it is desirable to reduce the voltage and current stress on each switch and passive components. Third, there is a need to reduce the number of external components for compact size. In [1] and [2], an external capacitor array for impedance matching occupies a large printed circuit board (PCB) area. If the output power is as high as 100W, the controlled switch needs to withstand high voltage stresses of up to 600V. The fractional-capacitance tuning technique in [3] achieves a wide range of equivalent capacitance, but there are still high-voltage-stress problems similar to [1], [2]. Although [4] provides a high-power solution, the voltage-controlled-capacitance (VCC) technique needs to tune the internal parasitic capacitance, $\mathrm {C}_{\mathrm {OSS}}$, from 350 to 3500pF and thus requires more external components and large bias voltage $\mathrm {V}_{\mathrm {BIAS}}$.