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Optimal Trajectory Control of LLC Resonant Converter for LED PWM Dimming

Fig. 1. MC3 LLC resonant converter LED driver with PWM dimming control.
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.


Fig. 2. Optimized pulse pattern for LED PWM dimming.
Fig. 3 State-plane trajectory of optimal LED PWM dimming control.
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