具適應性電壓回授控制之脈衝電流式LED驅動器

Pulse Current LED Driver with Adaptive Voltage Feedback Control

陳子軒(Tzu-Hsuan Chen)

指導教授 ： 劉邦榮

國立臺北科技大學/電資學院/電機工程系所/碩士(2014年)

https://doi.org/10.6841/NTUT.2014.00920

摘要

本論文提出一具適應性回授控制之脈衝電流電路來驅動LED燈串。整體電路由升壓型直流-直流轉換器、適應性回授控制電路及脈衝電流式驅動器所組合而成。脈衝電流概念為使調光電晶體導通時間更為短暫，並且使調光電晶體操作在歐姆區，使其汲源端跨壓更小，如此不僅可以有效降低調光電晶體的導通損失，亦可降低LED燈在長時間使用所釋放的熱能損失。LED燈在長時間使用下，將導致順向導通電壓下降。當LED燈串的輸入電壓為一固定電壓，將使得調光電晶體汲極端電壓增加，如此將增加LED驅動器的功率損耗。所提出的適應性回授控制可動態調節轉換器之輸出，使得調光電晶體之功率損耗不會隨著LED燈串之順向導通電壓下降，而造成不必要的能量損失。
晶片以TSMC 0.35 μm 2P4M CMOS製程來實現，其面積為1.251×1.209 mm2，轉換器採用升壓型，操作頻率為100 kHz，調光頻率為2 kHz，脈波電流為200 mA。所提出的脈衝電流驅動電路的脈衝頻率為1MHz，其最大脈衝寬度為500 ns。由模擬結果可知，當LED燈串跨壓下降180 mV時，藉由適應性回授控制，可使升壓型轉換器之輸出電壓亦下降180mV。與傳統PWM調光方式且為一固定電源之LED驅動器相比，本論文所提出之適應性電壓回授控制之脈衝電流方式能有效降低調光電晶體之能量損失，並且提升LED驅動器之效能至89.3%。因此，結合適應性回授控制之脈衝電流技術可實現高效率的LED驅動器。

關鍵字

LED驅動電路 ； 適應性控制 ； 最低電壓偵測器 ； 升壓型轉換器 ； 脈衝電流 ； 電流限制電路

並列摘要

This paper proposes a pulse current circuit with an adaptive feedback control to drive LED strings. The circuit consists of a dc/dc boost converter, an adaptive feedback control circuit, and pulse current drivers. The concept of the pulse current is to shorten the on-time duration of dimming transistors and to make dimming transistors operate in triode region to decrease its drain-source voltage.¬¬¬ It is not only to reduce conduction loss of dimming transistors but also to decrease thermal loss of LEDs used in long period. The forward voltage of LED used in long period will decrease. When the input voltage of LED strings is constant value, the drain voltage of the dimming transistors will rise, resulting in increasing power consumption of the LED driver. The adaptive voltage feedback control is presented to dynamically adjust the output voltage of the dc-dc converter. Hence, a redundant power loss of dimming transistors can be prevented even though the total forward voltage of the LED string decreases.
The chip is implemented with TSMC 0.35 μm 2P4M CMOS process, and its size is 1.251×1.209 mm2. A boost converter is used, and the operating frequency, dimming frequency, and the pulsating current are 100 kHz, 2 kHz, and 200 mA, respectively. The pulse frequency and the maximal pulse width of the proposed pulse current driver are 1 MHz and 500 ns, respectively. According to the simulation results, when the voltage across a LED string decreases 180 mV, the output voltage of the boost converter also reduces 180 mV with the adaptive feedback control. Compared with a constant source voltage of LED drive for traditional PWM dimming method, this paper presents an adaptive feedback control with pulse current technique can effectively reduce energy loss, and increase efficiency of LED driver to 89.3%. Hence, combining the adaptive feedback control and pulse current technique can achieve a high efficient LED driver.

並列關鍵字

LED driver ； adaptive control ； minimum voltage detector ； boost converte

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