High Density USB-PD ZVS Flyback Converter Based on Seconary Side Control

This paper presents a zero-voltage-switching (ZVS) USB-PD Flyback converter with a secondary control method for variable output voltage and loading. The PD chip at secondary side integrates both primary PWM and Synchronous Rectifier (SR) control function to achieve ZVS of primary main power switch, which simplifies the circuit and reduces the switching losses. Comparing to the based primary ZVS technique, the secondary control method eliminates the auxiliary winding and ZVS switch at primary side and prevents the synchronous rectification MOSFETs’ gate driver from being falsely triggered. Due to ZVS, high switching frequency can be enabled to use smaller size transformer and capacitor to get high power density for PD charger together with GAN switch. The detailed operation principle and design considerations are presented. Performance of the proposed control method is validated by the experimental results from a 5-20V/3.25A prototype.