具有平均電流校正技術之高效率單電感多輸出降壓型發光二極體驅動電路

Abstract

隨著照明元件的發展，發光二極體因其具有高壽命、高色彩飽和度等優點，已經取代傳統白熾燈泡成為照明系統的主流。在現今的顯示系統中也多以發光二極體來取代傳統冷陰極螢光燈管以提高顯示器的色彩品質。現今，發光二極體的驅動電路已經非常成熟。但在傳統的產品中均須要以單一電感來驅動單一顆發光二極體。這個限制使的照明與顯示系統無法有效的微小化及普及化。 近年來，開始有研究將單電感多輸出穩壓器的架構套用至發光二極體驅動器上。其中有使用一個電壓穩壓器搭配多組並連輸出的電流原來達到多輸出的效果。但各組電流源在電流上升時效率會急遽下降，因此這種架構通常只被使用在較低亮度的應用中。另一種被採用的架構為使用分時多工控制的多輸出切換式電源驅動器。此種驅動器雖然能夠操作在較大的電流下，但因為分時多工的限制，電感電流不能同時被所有輸出所利用，並且調光頻率與色彩解析度將大幅下降。 為了解決這些問題 本論文提出了一個單電感多浮動輸出降壓型發光二極體驅動器。其架構使電感電流能夠同時的被所有發光二極體所利用，大大的增加模組的發光效率。此外，所提出之平均電流校正技術能夠針對不同的調光條件下動態校正發光二極體的平均電流，消除因為調光而造成的電流交越變動。再者，各組輸出均能夠獨立的任意調光。最後，提出之單電感多輸出發光二極體驅動器在RGBW的應用中能夠提供24bit色彩解析度、12W的輸出功率，並且維持96%的高效率水準。

With the evolution of the lighting components, light-emitting diode (LED) has replaced the conventional filament bulb to become a mainstream of the general lighting system. Recently, LED is widely used in many applications like display systems, automotive headlight systems, projector and so on. These widely use of LED make the LED driver circuits much well-developed and stable nowadays. But in conventional product of LED driver, it needs one inductor to drive one LED. This limitation results in the obstacle of the size-reducing and popularization. In recent years, may researches have focused on the single-inductor multiple-output (SIMO) LED driver topology to break through the restriction of the size and cost. One method is to use a voltage regulator with multiple paralleled current sources to drive LEDs independently. However, the efficiency will drastically decrease when the output current raise. Another method is to use time-multiplexing (TM) control multiple-output switching regulator. This topology can provide larger output current but the inductor current will separate to several parts and can’t be used simultaneously. Furthermore, the limitation of TM control also results in the low dimming frequency and low color resolution. In order to solve these problems, a single-inductor multiple-floating-output (SIMFO) LED driver with average current correction (ACC) technique is proposed in this dissertation. The inductor current can be utilized by every LEDs simultaneously, enhancing the luminous efficiency. Furthermore, proposed ACC technique can adaptively adjust the average current, eliminating the current cross regulation (CCR) effect which always happens in different dimming states. Moreover, each output can dim individually. Last, the proposed LED driver can achieve 24bit color resolution, 12W output power and maintain 96% high efficiency in the RGBW application.