A TRIAC-Dimmable LED Lamp Driver With Wide Dimming Range

LED light bulbs are becoming increasingly popular as they consume much less power than traditional incandescent lamps. To enable full compatibility with incandescent lamps, apart from delivering the same light output and quality, they are expected to be operable with standard TRIAC-based light dimmers. However, the input current of the LED light bulbs at dimming could fall below the holding current of the TRIAC, resulting in limited dimming range and lamp flickering. This paper presents a TRIAC-dimmable LED lamp driver allowing wide dimming range. The concept is based on controlling the input reactive power, so that the input current is increased to a level higher than the holding current of the TRIAC, while the LED array power is regulated. The driver consists of two power conversion stages, including a four-quadrant ac-dc converter for shaping the input current and a resonant converter for regulating the output power to the LED array. The two converters share the same switching network. Modeling, analysis, and design of the driver will be presented. An LED prototype has been built and evaluated. Experimental results reveal that the true firing angle of the TRIAC can be adjusted down to 172°, and the lamp power can be dimmed from 7.2 to 0.3 W linearly.