In the past, the traditional wireless charging scheme used in the market is the frequency conversion architecture, which can not realize the wireless fast charging function of the apple mobile phone. Apple 7.5W fast charging must be fixed frequency architecture. The fixed frequency has three modes: phase modulation, voltage regulation and duty cycle. Among them, the mode of phase modulation needs a large inductor, it is LCL mode, the inductor sacrificed energy, the efficiency is low, and the sound is relatively large; the mode of voltage regulation can make the duty ratio constant to 50%, and the interference to the mobile phone is the least. The duty cycle is the ratio of the upper tube opening time to the whole cycle in terms of the half bridge. Because it is the full bridge, the 50% duty ratio means that the transmission energy is the largest; the mode of occupying the space ratio is not 50%, but the change, and the transient is poor.