高效能適應性控制之冷陰極管驅動電路設計與分析

Abstract

冷陰極管目前正廣泛地被用來作為液晶顯示器的背光模組，並且液晶顯示器正是目前可攜式電子產品常使用的顯示器。尤其像是筆記型電腦和個人數位助理等電池供應產品更是不可或缺的裝置。因此，如何有效降低成本、縮小體積、提升效率、獲得較佳的可靠性和穩定地亮度是現階段設計所面臨的挑戰。然而，背光模組亦需具備過電壓保護及精確調光的控制機制。由於目前的液晶電視都要求大尺寸的顯示面板，因此傳統控制器效能已經無法滿足現今市場的需求。

本論文提出一種新穎的冷陰極管驅動電路架構，以達到穩定控制，而這是個值得深入探討的研究方向。此一控制電路建構於全橋式切換開關的架構。整體的控制電路分為全橋式切換開關、共振槽、諧振變壓器、智慧型零電壓切換電路、過電壓保護及調光控制器等。智慧型零電壓切換電路是針對在不同負載情況下，將回授訊號和參考位準做比較，再將其結果透過脈波寬度調變處理，產生最佳導通時間，進而改善整體系統效率。所提出之驅動電路架構能夠有效地預防冷陰極管開路的狀況發生，並且確保驅動電路不會受到損害。

與傳統架構相較之下，本控制電路在負載變化時，具有較快速的響應時間。並擁有低功率消耗與較低的誤差訊號電壓等效能。最後經由模擬證明，本系統能夠達到零電壓切換、快速反應時間、較佳效率、穩定的亮度及精確調光控制的目標。

Cold-Cathode Fluorescent Lamps (CCFL) is wisely used to provide backlight illuminate for the Liquid Crystal Displays (LCD), which are the famous displays in the portable devices. Especially, LCD is the important part in notebooks and personal digital assistants for battery powered instruments. The design challenges are how to reduce design cost and volume, how to improve efficiency, and how to get better reliable and stable brightness. Furthermore, the backlight modules also need over-voltage protection and accurate dimming mechanism. The performance of the conventional drivers is not good to meet the requirement of today’s LCD TVs because of the large size display panels. A novel inverter driver design for CCFL is proposed in this dissertation. The proposed ideas can achieve stable control, which is a worthy challenging research. The novel driver is based on the full-bridge architecture. The whole control system consists of a full-bridge switch, a resonant tank, a transformer, an intelligent zero-voltage switching (ZVS) circuit, an over-voltage protection and dimming controller. The talent zero-voltage switching controller compares the feedback signal with the reference voltage. Then, the comparison result of the two signals is modulated by pulse width modulation control (PWM), and generates optimum conduction time to improve the whole system’s efficiency. The architecture can effectively prevent CCFL from the open-lamp condition and protect the driver circuit from being damaged. Our CCFL resonant inverter controller has faster response time than the previous design when the load is changing. And it has a lower error signal voltage and lower power consumption. Finally, the simulation results reveal that the resonant inverter can achieve zero voltage switching, fast response time, good efficiency, stable brightness, and accurate dimming mechanism.