自主式恆定導通時間控制的高功率因數浮動式降壓型交直流轉換發光二極體驅動器

Abstract

由於發光二極體（Light Emitting Diode, LED）具有高效率、極長壽命、無汞且無需暖燈反應快、驅動電路簡單以及僅需控制額定的電流即可達到調光控制等諸多優點使其快速地普及於傳統的照明市場；然而當其大量應用於照明用途之後伴隨而來的問題則是許多舊有的驅動電路控制機制已不符合現今規範之需求。 本文旨在提出一個新型浮動式降壓型拓撲，並加入了自主性恆定導通時間(Automatic Constant On Time, ACOT)的控制技術使得降壓型拓撲可於IEC60950規範中的安全電壓(60V)之下達到高功率因數校正(Power Factor Correction, PFC)並符合IEC61000-3-2 Class C規範中對於各階諧波電流失真之要求。透過平均電流偵測(Average Current Sensing, ACS)的控制技術實際地偵測並控制流經發光二極體之電流使其於不同的輸入電壓條件及不同的輸出負載條件下都可達到極佳的電流調節能力，此控制技術也使得儲能電感不再受限於必須使用變壓器型式達到迴授控制。最後在本文中加入了快速啟動與供電維持模式(Fast Startup and VDD hold-up mode)的控制以達到極短的啟動時間以及非常寬輸出電壓範圍應用，附帶也減少了電路中的元件數量達到精簡驅動電路設計以及縮小電路板之需求。 本論文中所提及的控制電路實現於世界先進所提供之四百奈米製程並驗證了此控制技術於一個十瓦發光二極體的驅動電路中在寬範圍輸入電壓以及發光二極體負載變動超過50%的情況下都仍有小於2%的電流調節能力，並通過IEC61000-3-2 Class C之電流諧波規範，此外系統啟動時間更由原本的一秒之上縮短至五百毫秒以內。本文所提出新型浮動式降壓型拓撲之控制技術具有高效率、高功率因數、低諧波失真、極佳的電流調節能力與寬輸出電壓範圍應用以及精簡了驅動電路所需的元件與體積之諸多優點，並有效解決舊有控制技術所面臨的許多問題。

Lighting Emitting Diode (LED) is adopted in lighting applications popularly since it has the following advantages: high efficacy, long life, Mercury free, fast response, easy driving, easy dimming, and etc. However, conventional driving circuit cannot meet the recent standard and requirement. The proposed floating buck converter provides excellent performance as follows. The floating buck converter with the proposed Automatic Constant on Time (ACOT) control can achieve power factor correction (PFC) and the current harmonic distortion can meet the requirement of standard IEC61000-3-2 Class C when the LED voltage is lower than 60V, which is the safety voltage of standard IEC60950. By adopting average current sensing (ACS) control, the current flowed through LED is detected directly so the converter provides excellent current regulation under different input voltage and output voltage. Furthermore, the single winding inductor can be adopted, and it is not necessary to use transformer type inductor. Fast startup and VDD hold-up mode is embedded to reduce startup time and provide wide output voltage range. Moreover, it can reduce the external component count and the volume of the driver board. The proposed control circuit is implemented in V04 process, and it is verified on a 10W LED driving circuit. Its current regulation is lower than 2% under universal input and LED voltage varying 50%. The current harmonic distortion meets the requirement of standard IEC61000-3-2, and the startup time is reduced from one second to less than 500ms. The proposed floating buck converter can achieve high efficiency, high power factor, low current harmonic distortion, excellent current regulation, wide output voltage range, and reducing the external component count and the volume of the driver board.