Phase Controlled Piezoelectric Transformer Using in Backlight Inverter

• Main Authors: Sheng-Chi Su, 蘇聖琪
• Other Authors: 陳秋麟
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/48551999388304857487

碩士 === 國立臺灣大學 === 電子工程學研究所 === 94 === The backlight system is one of the most important parts in the liquid crystal display (LCD). It consumes most of the power of the whole system. To achieve higher power efficiency, piezoelectric transformers are utilized in the backlight systems. A piezoelectric transformer can be a high-efficiency power converter. Compared with a traditional electromagnetic transformer, it has many advantages such as lower electromagnetic interference (EMI), higher safety, and smaller volume. However, a piezoelectric transformer has the highest efficiency and the highest voltage gain only when it is operated around its resonant frequency. As a result, it is very important to maintain the operating frequency of a piezoelectric transformer. This thesis is focused on the application of the piezoelectric transformer in the backlight system. The relations between the phase difference of the input voltage and the output current, operating frequency, and voltage gain are discussed. A phase control strategy is also proposed. The control strategy uses the phase comparing with the input voltage signal and the input current signal to maintain the operating frequency of the piezoelectric transformer. We use the burst mode to regulate the brightness of the CCFL. We also ignite the CCFL and measure the efficiency in the experiment. The backlight system is one of the most important parts in the liquid crystal display (LCD). It consumes most of the power of the whole system. To achieve higher power efficiency, piezoelectric transformers are utilized in the backlight systems. A piezoelectric transformer can be a high-efficiency power converter. Compared with a traditional electromagnetic transformer, it has many advantages such as lower electromagnetic interference (EMI), higher safety, and smaller volume. However, a piezoelectric transformer has the highest efficiency and the highest voltage gain only when it is operated around its resonant frequency. As a result, it is very important to maintain the operating frequency of a piezoelectric transformer. This thesis is focused on the application of the piezoelectric transformer in the backlight system. The relations between the phase difference of the input voltage and the output current, operating frequency, and voltage gain are discussed. A phase control strategy is also proposed. The control strategy uses the phase comparing with the input voltage signal and the input current signal to maintain the operating frequency of the piezoelectric transformer. We use the burst mode to regulate the brightness of the CCFL. We also ignite the CCFL and measure the efficiency in the experiment.