LAUSR

At light load, the efficiency of LCC resonant converters decreases dramatically. The burst mode is a good choice to improve it. However, the burst frequency is changing at different loads, and the audible noise is unavoidable when the burst frequency enters into the audible range (20 Hz–20 kHz). In this article, according to the state trajectories of two steady-state modes, four different burst modes for LCC resonant converters based on trajectory control are proposed, which cover different power ranges. Then, the proposed state trajectories of four burst modes are described, and the width of burst on pulses is derived accordingly. By switching to different burst modes under different loads, the proposed adaptive burst mode can cover a much wider load range free of audible noise. Finally, to verify the proposed adaptive burst mode, an LCC converter prototype is constructed, which shows that the burst frequency keeps above audible range from 0.2% to 20% full load with efficiency improved.