DPLL Technique Applied to Backlight Module for Eliminating Temperature Effect in Piezoelectric Transformer

A new approach is proposed in this paper for eliminating the temperature effect in a single-stage backlight inverter using the digital phase-locked loop (DPLL) technique. First, a class E backlight inverter is employed to simplify the circuit and to raise the system efficiency. A piezoelectric transformer (PT) is used to drive the cold cathode fluorescent lamp (CCFL) to overcome the drawbacks of a conventional transformer and to reduce the dimension of the backlight module. Next, a DPLL 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 angle rather than a lamp current amplitude traditionally used. The complete analysis and design considerations are detailed.