The Tracking of the Optimal Operating Frequency in a Class E Backlight Inverter Using the PLL Technique

Chang Hua LIN  John Yanhao CHEN  

IEICE TRANSACTIONS on Electronics   Vol.E88-C   No.6   pp.1253-1262
Publication Date: 2005/06/01
Online ISSN: 
DOI: 10.1093/ietele/e88-c.6.1253
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit and Device Technologies)
Category: PLL
backlight module,  piezoelectric transformer,  phase-locked loop,  temperature effect,  

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A new approach is proposed in this paper for the tracking of the optimal operating frequency in a Class E backlight inverter using the phase-locked loop (PLL) technique. First, a new single-stage backlight module is introduced 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 eliminate the downside of a conventional transformer and to reduce the dimension of the backlight module. Next, a PLL 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. A simplified model, along with its design procedure, is next presented. The complete analysis and design considerations are detailed. Finally, it is rather encouraging to observe that the experimental results match our analytical solutions closely.