Eliminating the Temperature Effect of Piezoelectric Transformer in Backlight Electronic Ballast by Applying the Digital Phase-Locked-Loop Technique

A new controller for eliminating the temperature effect of a piezoelectric transformer (PT) in a backlight electronic ballast is proposed in this paper. First, a class-D backlight inverter is employed to simplify the circuit configuration and to raise system efficiency. Next, to reduce the dimensions of the backlight module for satisfying the thin-shaped design trend and to overcome the drawbacks of a conventional transformer, a PT is incorporated instead. Then, a digital phase-locked-loop (DPLL) controller is embedded into the backlight system as a feedback control mechanism to track the optimal operating frequency of the PT, so that the PT's temperature effect is removed; hence, system efficiency and stability is improved. The design considerations are detailed, and the experimental results confirm the validity of the proposed control strategy