| As a new green lighting products has significant advantages such as long life, high efficient, compact size, environmentally friendly, LED lighting it is now replacing the traditional lighting method in wild application situation. However, the rated power of individual LED is quite limited. Thus, multi-string LEDs are required in a single system to achieve expected luminaire performance. As the current through the LED strings has a close relationship with the loss and brightness, it is crucial to keep current balancing among the LED strings. With better LED current balancing, the application could achieve longer life, higher efficiency and consistent brightness. This project mainly study on the current sharing technology for multi-output LED driver.Categorized the existing current sharing method into active and passive method, these current sharing method has many advantages. The passive methods which based on charge-balance capacitor has lower cost and simpler structures, the active methods have a superior load adaptability and easier to expand. Based on these advantage of two methods, a novel hybrid current balancing method for multi-channel LED drive is proposed. The proposed structure is based in AC bus and each output module are independent. A switching mode current regulator is adopted for each output module to balance the currents of the output modules. Since the current regulator only process part of the total output power, the cost is low and the efficiency is high. Performance of the proposed method is validated by the simulation and experimental results from a120W prototype with four LED strings.In medium to low power LED lighting application, to overcome the insufficient of applying passive current balancing method in single ended topology such like flyback converter, a novel charge-balance capacitor based current sharing method is proposed and applied to flyback converter. Precise current sharing and simpler structure is achieved. Meanwhile the control of the current sharing method and electrical connection is simplified, thus the cost is decrease. Performance of the proposed method is validated by the experimental results from an8W prototype with four LED strings.In some LED lighting application based on RGB independent control, the multi-output LED strings need more flexible current control to achieve the independent adjustment of the color. Based on the study of multi-output constant voltage output method on flyback converter, a novel multi-output current control method is proposed. By using the time sharing operation mode and secondery side post regulation method, multi-output current sharing can be achieve. Performance of the proposed method is validated by the experimental results from a27W prototypeAt last, this paper gives a summary of these current sharing methods. |
