Achieving maximum-efficiency tracking control for backlight electronic ballast with phase-locked loop techniques

Single-stage electronic ballast with maximum-efficiency tracking is proposed in this paper. The original backlight system incorporates a phase-locked loop (PLL) as a feedback mechanism to promote the system efficiency and stability. To overcome the drawbacks of conventional electromagnetic transformer and miniaturize the backlight module, the piezoelectric transformer (PT) is adopted for driving the cold cathode fluorescent lamp. In addition, the PLL is used to track the optimal operating frequency of PT for achieving maximum output efficiency. The feedback parameter used in the presented system is the phase component instead of the lamp current amplitude utilized traditionally. A simple model and design procedure are both constructed by reasonable parameter simplification and combination schemes. Complete analysis and design considerations are discussed in detail in this paper. Experimental results are close to the theoretical prediction.