Non-linear feedback control of robust bi-color LED lighting

Light-emitting diode (LED) technology involves highly complex interactions of heat, light, power and color. Dimming a bi-color LED system with color mixing feature will alter the power and junction temperatures, which in turn shift the color spectra of the LEDs. In this paper, a closed-loop control method based on the nonlinear empirical LED model is proposed for decoupling the dimming control and color control of a bi-color system comprising warm-white and cool-white LEDs. The proposed control scheme has been successfully implemented to provide highly precise and independent control of dimming and correlated color temperature (CCT). Even considering significant changes in ambient temperature, the maximum errors in luminous flux and CCT employing the proposed method are around 3% and 1.78% respectively while the corresponding errors using an existing linear duty-cycle control method are 20% and 27.5% respectively.