A Simple Brightness and Color Control Method for LED Lighting Based on Wireless Power Transfer

This paper proposes a simple and low-cost brightness and color control method for a wireless light emitting diode (LED) system. Since the open circuit voltage of the LED in the secondary side is approximately constant, the average current flowing through the LED reflects the average power received from the proposed wireless power transfer system. The brightness of the LED is adjusted by using a pulse width modulation (PWM) average power control method from the primary side directly. The same inductively coupled channel is utilized to establish a wireless communication channel to control the LED color based on a time-division multiplexing method. A wireless communication protocol is defined, and the worst-case condition for designing the primary PWM modulator identified to avoid the misinterpretation by the secondary demodulator between the power regulation and signal transfer. Experimental results have demonstrated the whole dimming capability of the proposed system with full range duty cycle regulation, and a three digit wireless communication channel developed in this paper can effectively control the selection of eight colors.