A circuit includes a bridge circuit, a converter, and a controller. The bridge circuit receives power from first and second power lines of a switch and generates a rectified voltage. The switch is capable of operating in a first state in which the switch conducts power to the first power line but not the second power line, a second state in which the switch conducts power to the second power line but not the first power line, and a third state in which the switch conducts power to both the first and second power lines. The converter converts the rectified voltage to an output voltage to drive a light source, and controls a current through the light source according to a driving signal. The controller monitors the operation state of the switch and generates the driving signal based on the operation state to control brightness/dimming of the light source.