Constant Burst Frequency Control for LLC Converters with Trajectory Control

The light load efficiency has drawn more and more attentions for the LLC resonant converters. The conventional burst mode control usually suffers from current overshoot and low efficiency during burst-on time, load-depended burst frequency which may generate audible noise. In this paper, an adaptive constant burst frequency control method based on the trajectory control is proposed. The burst frequency can be kept at pre-set frequency, and the resonant tank is operated at pre-set optimal load point during burst-on time. Experiment results of the proposed method are verified by a 100kHz 1kW LLC converter.