Design of Class E Backlight Module With Optimal Operating Frequency Tracking Mechanism

This paper proposes a new control approach for tracking the optimal operating frequency of a backlight inverter. First, a class E backlight module is introduced to simplify the backlight circuit and to raise the system efficiency. A piezoelectric transformer (PT) is used to drive the cold cathode fluorescent lamp (CCFL) to eliminate the drawbacks of a conventional transformer and to reduce the dimension of the backlight module. Next, phase-locked loop (PLL) technique is embedded in the backlight system, as a feedback mechanism, to track the optimal operating frequency of the PT so that the PT´s temperature effect is removed and, hence, the system efficiency and stability is improved. The feedback variable proposed is a phase difference rather than lamp current amplitude traditionally used. The complete analysis and design considerations are detailed.