Comparative study on sinusoidal and square wave driving methods of EEFL(External Electrode Fluorescent Lamp) for LCD TV backlight

Abstract

LCD (Liquid Crystal Display) panels are used in various applications ranging from smaller portable electronic equipment to larger fixed location units. The LCD panel itself cannot emit light. Therefore, a backlight system that supplies the light from behind is normally required. Currently, the most commonly used light emitting device is a fluorescent tube called a EEFL (External Electrodes Fluorescent Lamp). EEFL is mostly driven by sinusoidal wave driving method although EEFL can be driven by both sinusoidal wave and square wave. The sinusoidal wave driving method reduces the cost and allows more power efficiency since this driving method can reduce the voltage stress of EEFL inverter switches and achieve the soft switching of the switches. However, a transformer should be used in the inverter since a high voltage should be applied to the both ends of EEFL to turn on the lamp. And the power loss mainly occurs at the transformer in the sinusoidal wave driving method. As the transformer is removed, a square wave is applied directly to the both ends of EEFL by a cascaded three-stage inverter. And if EEFL is driven by a square wave, a change of driving frequency and voltage can be easily controlled. Therefore, the characteristics of the luminescence and discharge would be easily examined. And In the case of square wave, the high luminance and light efficiency can be obtained. In this thesis, a comparative analysis between the sinusoidal and square wave driving method will be presented. And also, the luminescence and discharge characteristics of EEFL driven by square wave will be analyzed from the experimental results.