A Bulk-Capacitance Reduction Method Using Self-Driven Thyristor for AC-DC Converters

Abstract

Universal serial bus power delivery (USB-PD) fast chargers equipped with wide-bandgap devices are driven to higher power density and efficiency to be more competitive in the market. The indispensable bulk capacitors used to smooth rectifier output usually come with large capacitance that could take up to 35% of the total system volume. To further the system-level miniaturization and performance improvement, it is essential to reduce the bulk-capacitor size. This paper discusses a simple-to-implement method to extend the line-voltage conduction and reduce the bulk capacitance, using a self-driven thyristor including a silicon controlled rectifier (SCR), an anti-parallel diode and a Zener diode without any control circuits. Design analysis is presented, and the design procedure is implemented to build a 60-W GaN-based active-clamp flyback converter. The measurement results on the prototype show a 36.4% reduction of the bulk capacitance and 27.8% reduction of the total volume with similar efficiency compared to the conventional AC-DC solution. A detailed design guideline is also provided in this paper.