Highly Integrated ZVS Flyback Converter ICs With Pulse Transformer to Optimize USB Power Delivery for Fast-Charging Mobile Devices

Flyback converter with USB power delivery is widely used for fast-charging mobile devices. However, conventional solutions have issues such as lower efficiency, higher cost, a large number of external components, and lower loop gain bandwidth. In this article, a high-efficiency zero-voltage switching (ZVS) flyback converter with primary- and secondary-side control ICs is proposed to solve the aforementioned issues with high integration level. The proposed control replaces optocoupler to achieve ZVS and secondary-side-regulation (SSR) by a pulse transformer. The ICs further integrate the USB power delivery (PD) controller and the constant voltage (CV)/constant current (CC) loop compensation to reduce external components. The proposed control and small-signal model are illustrated and verified by the experiment. The control ICs were fabricated in a 180-nm BCD process. The implemented 20-V/3-A/60-W USB PD flyback converter achieved 93.5% maximum efficiency using Si power switches. The feasibility of the proposed converter is verified by a thorough test of programmable power supply (PPS) with various CC/CV levels and load/line transients.