Discussion of Junction Capacitance of SiC Schottky Diode on Soft-Switching Condition of LLC Resonant Converter with Cockcroft-Walton Voltage Multiplier for High-Voltage Generator

The combination of LLC resonant converter and Cockcroft-Walton voltage multiplier (CWVM) as a high-voltage generator (HVG) can realize soft switching and low voltage stress on transformer as well as rectifier. Experimental results have indicated that the junction capacitances of diodes in the CWVM show a significant impact on the soft switching condition. In this paper, a detailed analysis for the LLC converter with the consideration of parasitic capacitance Cp (including diode junction capacitance and transformer winding capacitance) is conducted, which is called as LLC-C converter in this work. The theoretical analysis shows that a double pole in a relatively high frequency is introduced, especially at the light load. At the heavy load, the LLC-C converter operates similar to the LLC, and the effect of Cp can be neglected. It is also verified by the experiment with a 24-V/2-kV HVG prototype.