應用於場色序法(FSC)RGB LEDs背光模組之反饋節能技術

Abstract

使用色序法(FSC)技術之 RGB LED顯示器背光源模組可得到較傳統光源(White LEDs /CCFL)佳色彩顯示飽和度與較廣色域。也由於移除了彩色濾光片，故顯示器亮度可提升約為原來使用濾光片架構顯示器的三倍。除此之外顯示器功耗與成本皆可因彩色濾光片的移除而大大減低。針對具FSC技術之 RGB LED顯示器背光源模組，本文所提出之能量反饋(ER)技術可在每個色序顯示時序內動態切換輸出電壓於36伏特以供應12顆串聯使用之綠光與藍光LED，和切換為24伏特以供應12顆串聯使用之紅光LED。由此得以節省紅光顯示時之功耗，讓整體功耗減低13%。 在ER技術實踐上，現今商業晶片尚無法滿足ER技術所需之所有功能；因此加入可驅動獨立上/下橋高功率MOS並具固定驅動間隔時間之商業驅動晶片IR-2184，使系統具備同步整流(SR)控制功能，才得以實現ER技術之基本系統需求。更進一步則使用ER控制取代商業上AC-DC 轉換器控制，其可操作於臨界導通模式(BCM)，並具觸發下一切換週期之零電流檢測(ZCD)功能。而此ZCD功能是藉由高效電流感應(ECS)電路實現，其得以滿足系統控制需求並得以驗證此能量反饋技術可行性。故本文所提出之ER技術可將原本輸出電壓從36V伏特切換至24伏特間輸出電容欲耗費之能量儲存於能量反饋儲能電容，亦可增進電壓切換穩定速度；也因此可更進一步減低功耗至17%。而建構此技術僅需增加一反饋儲能電容與蕭特基二極體於昇降壓電源轉換器架構上。

The field sequential color (FSC) technology with RGB-LED backlight modules can achieve high color saturation and better color gamut compared to conventional cold cathode fluorescent lamp (CCFL) backlight. Owing to the remove of color filter, the display brightness can be promoted to about three times that of the original one with color filter. Besides, both display power consumption and cost can be decreased greatly due to the disappearance of color filter. The proposed energy-recycling (ER) technique for the FSC display with RGB-LED backlight modules can dynamically switch the output voltage to 36 V for twelve green/blue LEDs in series or 24 V for twelve red LEDs in series according to each color sequence in the FSC technique. As a result, it can reduce 13% of total energy during the red color display period. The current commercial chip can’t satisfy all the functions in the ER technique; thus, a fabricated ER-controller with a commercial IR-2184 driver, which is used to drive independent high/low side power MOSFET with a fixed dead time, synchronous rectification (SR) control function, can implement the ER technique to meet the basic requirement of system. The ER control, which is used to replace the commercial AC-DC converter control further, can operate at the boundary current mode (BCM) with a zero current detection (ZCD) function to trigger the next switching cycle. The ZCD function is achieved by the enhanced current sensing (ECS) circuit, which can satisfy the need of system control to prove the feasibility of the ER technique. The proposed ER technology can accelerate the settling time of the output voltage since the energy that needs to be dissipated by load or leakage is stored to an energy-recycling capacitor from the output capacitor when the driving voltage is switched from 36 V to 24 V; that is it can further reduce 17% of dissipation energy. Specially, it only uses one recycling capacitor and one Schottky diode connected at the power structure of synchronous buck-boost converter.