Capacitor-isolated structure with brightness and color controlling for multicolor LED strings

A capacitor-isolated structure with brightness and color controlling for multicolor LED strings is proposed. Such structure mainly plays the role of current-balancing and color mixing. Moreover, in order to decrease the color shift, the current amplitude of LED strings is controlled constant. The luminous flux and chromaticity coordinates are regulated through controlling the sum and ratio of duty cycles respectively. The capacitors in the structure have three functions: current-balancing, galvanic isolation and resonant. The proposed topology have the energy-recycling function to assure that any LED string can be totally turned off which makes it possible that arbitrary chromaticity coordinates in the color gamut can be achieved. A prototype with red, green and blue strings has been built and evaluated. Experimental results show that the duty cycle of every string can be 0 to 1. The luminous flux can be from 100lm to 600lm, and its error is within ±3%. Arbitrary chromaticity coordinate within the triangle enclosed by RGB points can be realized.