Balanced driving system for multiple cold-cathode fluorescent lamps

A novel scheme to drive the lamps for liquid crystal display (LCD) backlight modules is shown in this paper. The driving scheme connects multiple cold cathode fluorescent lamps (CCFLs) in series, with the aim to alleviate the influence of parasitic capacitance induced in between the interface of lamps and the aluminum back-plank and thus to balance the lamp currents and light output. The series-connected lamps will flow identical arc currents despite of their impedance discrepancies. In addition, the lamps are connected in a special order according to their physical locations so as to obtain matched leakage capacitances and equalized leakage currents. The topology is capable of driving an arbitrarily even numbers of lamps with the same lamp current, while achieving significant size, weight, and cost reduction. Finally, the driving scheme is verified by experimenting on a backlight module with four L-type lamps in a 19-inch LCD. The experimental results demonstrate the effectiveness and feasibility of the current balance scheme.