A line and load independent constant-frequency zero-voltage-switching series resonant converter

Frequency modulation is often used in series resonant converters to gain output voltage regulation. Variable frequency however brings challenges for EMI filter and switch driver design and the desirable zero voltage switching cannot be maintained at light load conditions. This paper presents time-domain steady-state analysis of fixed-frequency series resonant converters with phase shift modulation. Three operation modes are identified and the mode boundaries are demonstrated. Based on this a passive robust auxiliary circuit is proposed to ensure the zero voltage switching of the converter in all three modes. The achievement of zero voltage switching is confirmed by experimental results.