Hold-up Time Compensation Circuit of Half-Bridge LLC Resonant Converter for High Light-load Efficiency

This article proposes a half-bridge LLC resonant converter applying a simple circuit with a variable magnetizing inductance scheme for hold-up time requirement. By changing the magnetizing inductance of the main transformer, the proposed converter can satisfy the hold-up time requirement without sacrificing efficiency, featuring small conduction, and turn- off switching losses of the primary switches in the nominal status. In addition, the proposed converter can relieve the burden of the additional components by positioning them on the signal path, and the proposed circuit is self-powered by adding only one additional winding instead of the isolated power supply. Therefore, those of the size and cost of the proposed circuit can be reduced compared to the previous studies. The feasibility of the proposed method was verified with a 350 W prototype converter (56 V/6.25 A), and the improved circuit for the transient mode was also presented. The experimental results validated the theoretical analysis and showed the effectiveness of the proposed converter for high-efficiency applications, especially in light-load conditions.