以具雙耦合電感SEPIC轉換器進行汽車LED頭燈之
設計與應用

針對高功率白光LED逐漸成為汽車頭燈市場主流之發展趨勢，本論文提出一種具有創新拓樸的SEPIC轉換電路，作為汽車LED頭燈之驅動器。所提汽車頭燈照明系統由汽車電力網路、SEPIC轉換電路、數位控制與調光電路、以及LED負載模組組成。SEPIC電路使用雙耦合電感設計，其中初級耦合電感用於電力轉換，均流耦合電感用於左、右頭燈電流平衡，另加入第三繞組處理洩磁回生。調光電路擷取汽車速度訊號進行零速調光，於汽車停等時間調降頭燈亮度至50%，並於起步後恢復常態，以收節能之效。本論文除進行SEPIC轉換電路分析、設計與模擬外，並實作原型電路以驗證理論設計，包括兩組輸出規格為40W/18.5V/2200mA與40W/28.5V/1400mA之SEPIC電路，分別驅動左、右兩組LED近燈與兩組LED遠燈。電路穩壓控制分別以類比IC TL494與數位訊號處理器TMS320F28035完成，零速調光則以數位PWM調控負載電流方式進行。LED近光採用Bridgelux公司的三串兩併7W/700mA暖白色LED模組，遠光燈採用Citizen公司的兩併20W/1100mA白光LED模組。原型電路經實測後，波形與理論預測相當一致，左、右頭燈均流效果良好，滿載時近燈與遠燈驅動電路的效率皆在90%以上，半載調光效率為93%，近燈滿載光通量為2400流明，遠燈則為3000流明，滿足國際規範要求。

關鍵字

汽車LED頭燈； SEPIC轉換器；耦合電感；均流控制；零速調光

並列摘要

Along with the trend the high power white LED is taking position ad the mainstream in the automobile headlight market, this dissertation aims to develop an SEPIC converter with innovative topology for LED headlight driving. The proposed headlight system consists of automobile power-set, SEPIC power converter, digital control circuit, dimming circuit, and LED load module. The innovated SEPIC converter is designed with dual coupled inductors. While the primary coupled inductor is used to convert energy, the current-sharing coupled inductor is applied for current balancing between the right and the left LED headlight. A third winding is included as well in the inductor for de-magnetization and energy recovery. Dimming to half output of the LED headlights while automobile is running at zero speed is Incorporated in SEPIC drivers in order to reduce unnecessary power consumptions. Except analysis, design and simulation, prototype SEPIC converter is Implemented for theoretical verification. The prototype comprises two sets of SEPIC converter with rating 40W/18.5V/2200mA and 40W/18.5V/1400mA, which are used respectively to drive high beam and low beam LED module. Converter voltage regulation is realized by analog IC TL494 and digital signal processor TMS320F28035. The zero speed dimming is accomplished by PWM current control. In terms of LED load, the low beam Bridgelux 7W/700mA LED module is connected with 3 LEDs in series and 2 LEDs in parallel. The high beam Citizen 20W/1100mA LED module is connected with 2 LEDs in parallel. As a result, the measured converter waveformss confirm the theoretical design, and consistency of load currents in different headlight is obtained as well. The measured converter efficiency at full load is 90%, and is 93%at half load. The low beam flux at full load is metered at 2400 lm, and 3000 lm for high beam flux, which satisfies the internations LED headlight code requirement.