Design of Boost Power Factor Corrector and Asymmetrical Half-Bridge Flyback Converter for USB-PD Applications

USB power delivery (USB-PD) chargers have a wide output voltage range for various charging applications. In this paper, a two-stage converter for USB-PD is implemented to meet the requirement of harmonic standard IEC61000-3-2. The front stage is a boost power factor corrector (PFC) to improve the power factor, and the second stage is an asymmetrical half-bridge flyback (AHBF) converter which can achieve soft-switching operation for output voltage regulation. The operating principles and control methods of AHBF for achieving primary-side zero-voltage switching and secondary-side zero-current switching are presented. In addition, the key parameters for AHBF converter are optimized, and the PFC stage is disable in light load condition to improve the system efficiency. Finally, a 240 W USB-PD 3.1 experimental prototype is implemented with ac input voltage of 90 ~ 264 Vrms with the output voltage/current of USB-PD 3.1. The experimental results show that the highest efficiency of the boost PFC converter is 97.2%. The highest power factor is 0.99 at full load condition. The maximum efficiency of AHBF is 91.3%, and the overall system efficiency can reach 88.6%.