Low-Frequency Square-Wave Drive for Large Screen LCD-TV Backlighting Systems

This paper presents a low-frequency square-wave drive, consisting of a single high voltage converter, an ac lamp ignition circuit, current control devices and a single backlight controller, capable of driving an arbitrary number of parallel cold cathode fluorescent lamps (CCFLs) with independent accurate lamp current regulation. Key to the architecture is a proposed capacitive coupling approach for ac lamp ignition that results in reliable, simultaneous ignition of parallel lamps with a maximum ignition voltage near the normal lamp operating voltage. A brief summary of the lamp model and behavior is presented to explain the findings during the capacitive ignition and low-frequency operation. Experimental results are presented demonstrating parallel lamp ignition and current regulation for four, 250 mm CCFLs.