Resonant full-bridge synchronous rectifier utilizing 15 V GaN transistors for wireless power transfer applications following AirFuel standard operating at 6.78 MHz

Abstract

Abstract-Connectivity in smart devices is increasingly realized by wireless connections. The remaining reason for using connectors at all is for charging the internal battery, for which wireless power transfer is an alternative. Two industry standards, AirFuel and Qi, exist to support compatibility between devices. This work is focusing on the AirFuel standard, as it is operating at a higher frequency (6.78 MHz), than the Qi standard, and therefore allows smaller passive components, including the coupling coils. Whereas gallium-nitride (GaN) devices are being widely used on the transmitter (Tx) side, this work uses low voltage GaN transistors on the receiver (Rx) side to allow synchronous rectification and soft switching, thereby achieving high efficiency. After analyzing adequate Class-DE rectifier topologies, a Class-DE full-bridge 5 W rectifier using 15 V GaN transistors are designed and implemented. The experimental results show an efficiency above 80 % over a wide operating range and a peak efficiency of 89 %, at an arbitrary alignment of Tx and Rx coils with 3 cm distance between them.

Synchronous Rectifier for High-Frequency Switch-Mode Power Supplies Using Phase-Locked Loops

“…The rectifier conducts both half waves of the sinusoidal input current and the resulting load on the inverter is almost increased by 4. This effectively halves the required peak output current of the inverter for the same output voltage, and significantly reduces the component stress, as discussed in [15]. The duty cycle of the power devices is desired to be as close to D d = 0.5 to achieve these benefit.…”

“…For this application the current driven rectifiers are of interest. They are usually split in three [15]. In Fig.…”

“…A SR can be implemented with so-called active-diodes [14], [15]. The active-diode is a MOSFET in parallel with a diode.…”