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Abstract

Maximum-efficiency tracking control applied in the backlight module is proposed in this paper. The backlight system incorporates a phase-locked loop (PLL) as a feedback mechanism to promote both the system efficiency and stability. To overcome the drawbacks of the conventional electromagnetic transformer and to miniaturize the backlight module, the piezoelectric transformer (PT) is adopted for driving the cold cathode fluorescent lamp (CCFL). To avoid the system efficiency decreases due to the temperature effect of PT, the PLL is utilized to track immediately the optimal operating frequency of PT for achieving maximum output efficiency under various ambient temperatures. The feedback parameter used in the presented system is the phase component instead of the traditionally employed lamp current amplitude. A simple model and the design procedures are both constructed by reasonable parameter simplification and combination schemes. Complete analysis and design considerations are discussed in detail in this paper. Experimental results agree with the theoretical prediction.

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