Fully Decoupled Current Control and Current Balancing of the Modular Structure for LED Color-Mixing System

Abstract

For LED color-mixing, the different color LEDs need to be controlled independently, so a fully decoupled current control and current balancing of the modular structure is proposed for LED color-mixing system. The capacitive current-balancing structure is combined with the quasi-boost converter to realize the decoupled current control and current balancing in each module. The capacitive current-balancing structure is based on the relative reactance of the capacitor with respect to the equivalent resistance of the associated LED string. The inductor in quasi-boost converter is used to further stable the output current flowing through each LED string, and the switch in quasi-boost converter for controlling the current of each LED string adopts the parallel connection to protect LEDs from the current-spike caused by the switch. The structure is modularity and scalability so that the different color LEDs can be added and removed easily. Compared with SIMO (Single-Inductor-Multiple-Output) structure, the proposed structure has no cross-coupling issues. The LED string currents working with PWM mode have a good current-balancing performance since the equivalent resistance of LED string is much smaller than the reactance of capacitors. In addition, the resonant capacitors separate the grounds of the power source and LED strings, so all the switches in parallel with LED strings do not need the isolated gate drivers. A prototype with RGB modules has been built and evaluated, and the experimental results have a good agreement with the theoretical analysis.