Research On The Constant Current Driving Method For General Buck-LED

With the wide application of LED, such as lighting and backlighting, there is a trend that it will replace the traditional lighting, owing to low dissipation, high efficiency, long life time and so on. The brightness of an LED is proportional to its forward current. In order to maintain the stability of its brightness, the constant current driver is the best choice. The LED drivers should be universal, avoiding repeating design.The design in this paper is mainly used for indoor lighting, driven by the grid, using Buck converter. In order to extend its application, the output current should be constant, regardless of input voltage, output voltage and the inductor. The traditional constant current control methods can’t meet the requirements, so this paper proposes a new closed-loop constant current control scheme. It uses floating Buck topology, belonging to peak current control, and the adaptive off-time keeps the output current constant. Two Toff control methods are proposed in this paper, and in order to simply the output current sampling, a new indirect output current sampling method is put forward.First, use direct output current sampling to verify the two Toff control methods. After that, change for the new indirect output current sampling. The theoretical analysis and simulation results have proved the validity using PSIM 9.0. Finally, choose one of the Toff control methods for experimental verification because of the time. The output current of the LED driver prototype is 400 m A, and the output voltage varies from 20 Vdc to 40 Vdc.