Optimal Trajectory Control of LLC Resonant Converter for LED PWM Dimming
Recently, the developers of many applications, such as display backlighting, indoor lighting and street lighting, have all favored multi-channel LED drivers. This paper proposes a novel PWM dimming solution with optimal trajectory control for a multi-channel constant current (MC3) LLC resonant LED driver. 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 dynamic oscillation when the MC3 LLC starts to work from the idle status, the first pulse-width of the gate driving signal is tuned based on the state-plane trajectory analysis. Thus the full-load steady state is settled within a minimal time. Under low dimming conditions, the LED intensity can be controlled more precisely.