固態光源之發光二極體具有優異的光電轉換效率、壽命長、包裝體積小、低消耗功率、耐震動及寬廣的溫度操作範圍等許多優點。近年來已逐漸完全的取代傳統冷陰極螢光燈，成為薄膜電晶體液晶顯示器背光模組的主流光源。隨著顯示器面板尺寸不斷提高，所需的LED使用數量也跟著增加，若只使用串聯結構方式使各顆LED電流相等，則所需的驅動電壓會很高。不但元件所需承受的電壓應力大，而且易降低LED的使用壽命及使得整個驅動器的可靠度下降，所以低壓多串並聯的LED驅動方式乃成為主要的背光電路結構選擇。在驅動多串並聯的LED燈管時，首要關鍵在於使各串擁有相同的電流，藉以實現均勻的面光源輸出，所以均流控制技術的導入，成為LED多串並聯時驅動之必需。此外，調光功能可以完成背光模組的省電及實現高對比的顯示要求。傳統的串聯調光方式，LED晶體常需承受全開與全關的電壓切換應力。不但容易在暫態過程損壞LED，而且驅動電壓範圍變動較大，因而輸出電容的能量充放範圍也變大。本論文研究以差模變壓器來實現兩通道LED串的並聯均流控制，並設計與LED並聯控制之調光電路。本論文實現並測試一原型電路以驗證驅動電路架構設計，由實測結果可以印證本文所提之均流效果與調光功能的可行性。

LED has many advantages such as high efficiency, long lifespan, low profile, low power consumption, well sustained of vibration and wide operating temperature range, etc. In recent years, LED has gradually to substitute traditional cold cathode fluorescent lamp then become a popular solution for the backlight source. For large size LCD panel displays, more backlight sources should be installed to provide required brightness. The series-structure is the common way to get high illumination, but it results a high voltage stress of components if there are many LED cascaded. Therefore, the parallel LED string with low voltage source is the most usual method. To uniform the LCD panel backlight, the brightness provided by each LED string must be equal. Hence the parallel LED strings must have a current balance control to produce identical luminance. Besides, dimming control is often needed to regulate the lumen level for contrast ratio and to achieve power saving. Conventionally, the dimming function is implemented by a dimming switch series connected with LED string. However the LED needs to suffer high switching voltage stress between complete turn-on and complete turn-off. Moreover, the charging and discharging of output capacitance with a wide range also shorten the lifetime. This paper aims to investigate a two-channel LED backlight driver with parallel dimming. A 10W LED backlight driver prototype has been built and tested to verify the feasibility of the studied driver.

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