Research On Hybrid Current Balancing Methods For Multi-output LED Driver

In nowadays, energy saving and environmental protection has attracted more and more attention. Due to the energy saving, low maintenance, compact size and environment friendly, the application of LED used for commercial and residential lighting becomes an irreversible tendency in the future’s lighting field. In high-power lighting application such as liquid crystal display backlighting, commercial and residential lighting, multi-channel LED drivers are needed to reduce the voltage of LED strings. Then, the current balancing is required for multi-LED strings to ensure LEDs have same light output. This project mainly aims at current sharing technology for multi-output LED driver, to explore the current sharing scheme with the advantages of simple structure, high efficiency and easy extension.Many methods have been proposed to achieve the current balancing among LED strings over the last few years. Basically, these methods can be divided into two catalogs, one is active method and the other one is passive method. Based on the analysis of these schemes, an improved precise passive current sharing method for multi-LED driver with voltage-doubler output configuration is proposed. The currents in one module are automatically balanced by the balancing capacitor and the currents of different modules are balanced by the coupled inductor. The experimental results from a120W prototype verified the theoretical analysisThis paper proposed a novel active current sharing method for multi-LED driver based on quasi-two-stage converter to achieve better load adaptability and higher efficiency. In this structure, the DC/DC converter that operates current-loop regulation only processes a small portion of the total power. By employing the partial power control and self-adapted bus voltage regulation, high efficiency and low cost can be achieved due to the low voltage stress, high switching frequency and smaller size of passive components. Performance of the proposed scheme is validated by the experimental results from an80W prototype with four LED strings. In order to combine the advantages of passive scheme and active scheme, a hybrid current sharing method based on AC bus is proposed. The currents in one module are also balanced by the balancing capacitor and the current sharing between different modules is achieved by DC/DC current regulator. Compared to the active method, the amounts of DC/DC converters can be cut in half. At the same time, the hybrid scheme has better load adaptability and easier to dim than passive method mentioned above. Finally, a closed loop simulation with bus voltage adaptive control scheme is built. The simulation results verify the feasibility of the scheme.At last, this paper gives a summary and comparison between these current sharing methods.