驅動高壓發光二極體之高功率因子積體電路

Abstract

在傳統LED (Light Emitting Diode) 照明的驅動電路之解決方法裡，最為人詬病的問題有三項: 首先是使用低電壓高電流，必須使用高功率LED，其該LED之散熱封裝成本高；其次是應用變壓器以降低橋式整流後的直流電壓，該變壓器占用相當多的空間；最後是使用大容量有極性的電解電容，長時間使用下，該元件壽命通常在兩年以下；而且在零下20度C以下的環境中，電解電容會失去電容功能。本論文目的是在探討於不使用變壓器及電解電容的情況下，如何利用高壓半導體製程設計出適用於LED照明應用之LED控制與驅動積體電路，並且評估其實用性與優缺點。經過各項電路模擬與設計計算，本論文提出以高電壓低電流之LED發光體為主體的控制與驅動概念，並且設計一款能直接承受高電壓的LED控制與驅動之積體電路，以驗證此設計概念。實際的量測數據顯示高電壓低電流為主體的LED控制與驅動電路可大幅提高功率因子在95%以上，能量轉換效率 (Efficiency) 約在90%，而使用90 lm/W的冷白LED燈珠時，其整體功效 (Efficacy) 約為80lm/W。雖然人眼無法察覺，但是此種設計方法會有120Hz的頻閃問題，因此如何在維持高功率因子的情況下又可以解決頻閃問題是未來可以探討的課題。

Conventional LED lighting drivers suffer three main drawbacks: (1). using low-voltage high-current LEDs with costly heat sink, (2). filtering rectified AC voltage by using a high capacity electrolytic capacitor which cannot work at very low temperature and has limited life time, and (3). employing a bulky transformer as energy converter. Here, we present a design scheme which includes a high-voltage integrated circuit controlling and driving high voltage, low current power LEDs without using electrolytic capacitor and transformer. To evaluate the feasibility, we design a prototype of the proposed high voltage integrated circuit to drive high voltage, low current LEDs. The experiment data demonstrate that: the power factor can reach more than 95%, the power efficiency is around 90%, overall efficacy is about 80lm/W in the case of using 90lm/W LEDs, and though, not visible by human eyes, 120Hz flickering of the LED light due to the intrinsic characteristic of the proposed design scheme is observed. Under the condition of no electrolytic capacitor and no transformer being used, the flickering problem is deserved further investigation in the future study.