Variable bi-level phase-shifted driving method for high-power RGB LED lamps

Based on the recently proposed bi-level driving method, this paper presents an extended version of the existing method, which is aimed at maximizing the luminous output of high-power LED lamps by piecewise-linear tracing of their luminous output curves under AM (amplitude modulation) driving. The proposed driving method divides the luminous output curve of an AM-driven LED into a multiple sections, where each section is approximated by a straight line with two predefined end-points acting as the lower and upper current levels as used in the existing bi-level driving method. The intermediate current and luminosity values lying between the upper and lower current levels are obtained by duty cycle mixing of the two current levels. The joined multiple sections has enabled a near-maximum luminous output to be extracted from the LED while a linear dimming is realized within each section. The proposed driving method is verified by implementation in a single-driver RGB color LED lighting system with the red, green, and blue LED driven in a time-sequential manner (or shifted in phase). Experimental results show that a significant gain in luminous efficacy, hence energy saving, is achieved compared to the commonly used pulse-width modulation (PWM) driving.