Optimal Trajectory Control of LLC Resonant Converters for LED PWM Dimming

In this paper, a novel PWM dimming solution with the optimal trajectory control for a multichannel constant current (MC³) LLC resonant LED driver is proposed. When PWM dimming is on, the LLC resonant converter operates under the full-load condition. The LED intensity is controlled by the ratio between the on-time and off-time of the PWM dimming signal. To eliminate the dynamic oscillations when the MC³ LLC starts to work from the idle status, the switching pattern is optimized based on the graphic state-trajectory analysis. Thus, the full-load steady state is tracked within the minimum time. Moreover, under low dimming conditions, the LED intensity can be controlled more precisely. Finally, the optimal PWM dimming approach is verified on a 200 W, 4-channel MC³ LLC LED driver prototype.