具有抑制低頻漣波及改善調光效率之LED驅動器

LED Driver with Low-Frequency Ripple Suppressed and Dimming Efficiency Improved

賴忠佑(Chung-Yu Lai)

指導教授 ： 胡國英

國立臺北科技大學/電資學院/電機工程系 電力電子產業研發碩士專班/碩士(2011年)

摘要

本論文係採用一般中低功率普遍使用的單級返馳式功因校正電路為主要架構，並採用工業界常使用的功因校正控制IC L6562來驅動約100W可調光之LED串列。同時，並針對單級功因校正電路之輸出電壓常存在兩倍輸入電源頻率的問題，加入一簡單、不會損失暨有的功率因數、亦不須額外控制的能量回收電路來改變瞬時輸出功率，以使得瞬時輸出功率能接近瞬時輸入功率，以降低輸出電容之充電和放電的能量，進而達到低頻漣波衰減的效果。因此，此轉換器能提供一穩定、準確的電壓回授信號給控制IC，並可提供一穩定電源來驅動LED照明串列，以避免低頻漣波影響到LED之色彩、亮度、壽命與可靠度。
就調光電路而言，採用場效可規劃邏輯閘陣列做為調光控制的核心，並於線性穩流調光電路中加入了閘極電壓偵測電路。根據調光命令及閘極之電壓變化來產生一個調變量，進而動態調整返馳式轉換器所須之電壓參考命令，以使得MOSFET之汲極與源極兩端的跨壓能隨著LED串列亮度降低而下降。也就是說，當負載變動時，亦或是當溫度變動而導致LED串列之等效導通壓降變動之時，所提之調光方式均能儘可能地使MOSFET工作於其輸出特性曲線之膝點，以降低MOSFET上不必要的功率損耗，進而達到改善效率的目的。於本論文中，首先藉由相關之理論推導分析後，再以電路模擬軟體來驗證所提架構之可行性與理論分析之正確性，最後以實作來驗證所提架構之有效性。

關鍵字

返馳式轉換器 ； 臨界導通模式 ； 單級功率因數校正 ； 能量回收 ； 低頻漣波抑制 ； 120Hz ； 輸出電壓調變 ； LED調光 ； 場效可規劃邏輯閘陣列

並列摘要

In this thesis, a single-stage power-factor-corrected (PFC) flyback converter is used as the main power stage, which is controlled by a control IC named L6562 so as to driver LED strings of about 100W. Since the output voltage of the converter possesses a double line frequency ripple, one energy recycling circuit without any control is added to make the instantaneous output power close to the instantaneous input power by changing the instantaneous output power, so as to reduce the energy stored/released in the output capacitor and hence to reduce the output voltage ripple with the double line frequency. Therefore, such a converter not only can provide a feedback control signal for the control IC, but also can supply the LED strings with a well-regulated voltage source such that the effect of the low-frequency ripple on the color, luminance, life and stability of the LED can be reduced.
For the dimming circuit to be considered, the field programmable gate array (FPGA) is used as a control kernel of LED dimming. At the same time, the gate voltage detecting circuit is added to the linear current regulator, so as to achieve LED dimming. According to the dimming command and the variation in gate voltage, the voltage reference command for the flyback converter is dynamically adjusted via a varying value created from FPGA, so as to make the voltage across the MOSFET reduced as the LED string is dimmed down. To speak lucidly, as the variation in load or the variation in temperature leads to the variation in equivalent forward voltage of the LED string, the proposed dimming method can make the voltage across the MOSFET operated at as near the knee point of the MOSFET output characteristic curve as possible, so as to reduce the power loss in the MOSFET and hence to increase the efficiency of the overall system. In this paper, first of all, the associated mathematical deduction of the proposed topology is given, secondly some simulation results are provided to verify its feasibility, and finally some experimental results are offered to demonstrate its effectiveness.

並列關鍵字

Flyback Converter ； CRM ； Single-Stage PFC ； Energy Recycling ； Low-Frequency Ripple Suppression ； 120Hz ； Variable Output Voltage ； LED Dimming ； FPGA

參考文獻

[3] H.-L. Cheng, Y.-C. Hsieh and C.-S. Lin, “A novel single-stage high-power-factor AC/DC converter featuring high circuit efficiency,” IEEE Transactions on Industrial Electronics, vol. 58, no. 2, pp. 524-532, 2011.

[4] B. A. Mather and D. Maksimović, “A simple digital power-factor correction rectifier controller,” IEEE Transactions on Industrial Electronics, vol. 26, no. 1, pp. 9-19, 2011.

[5] L. ber, Liu Gang and M. M. Jovanović, “Design-oriented analysis and performance evaluation of buck PFC front end,” IEEE Transactions on Power Electronics, vol. 25, no. 1, pp. 85-94, 2010.

[6] Hao Ma, Yue Ji and Ye Xu, “Design and analysis of single-stage power factor correction converter with a feedback winding,” IEEE Transactions on Power Electronics, vol. 25, no. 6, pp. 1460-1470, 2010.

[7] H. S. Athab and D. D.-C. Lu, “A high-efficiency AC/DC converter with quasi-active power factor correction,” IEEE Transactions on Power Electronics, vol. 25, no. 5, pp. 1103-1109, 2010.