無感測電阻之連續近似暫存器適應關閉時間控制技術應用於高效率高準確度發光二極體光源系統

Abstract

現今使用發光二極體來照明的光源系統已經愈來愈受到重視。使用發光二極體光源系統照明有許多好處，像是較低的功率消耗，以及較長的壽命。此外，由於其光譜中沒有紫外線和紅外線，既沒有熱量也沒有輻射，是良好的綠色照明光源，由環保的角度來看也是非常突出。 本篇論文提出了一種使用連續近似暫存器(SAR)來調變發光二極體驅動電路的關閉時間，使驅動電路可以準確的控制流經發光二極體的電流，並達到使整個系統的電源使用效率提升的作用。使用本篇提出的連續近似暫存器適應關閉時間控制技術，不需使用外部的電流感測電阻造成功率消耗，並且在輸入電壓或是串接發光二極體的數量改的之時，流經發光二極體的電流仍然穩定在一個準確的值。實驗結果顯示，電桿上的電流漣波保持在平均電流的±15%。本篇論文使用TSMC 0.25um 嵌入高壓 5V/40V CMOS製程技術來進行模擬和製作。提供電路使用的電源為八伏特到四十伏特，而可控制的輸出電流可以到一安培。

Light emitting diode (LED) lighting systems become more and more popular nowadays because of its many advantages such as low power consumption and long usage lifetime [1]. In addition, LED does not contain infrared and ultraviolet rays in its optical spectrum. That is, it only generates minimal heat and harmful radiation making it environmentally friendly. A successive approximation register (SAR) is utilized to control adaptive off-time in order to regulate accurate light emitting diode (LED) current and improve efficiency of LED driver. The proposed SAR-controlled adaptive off-time technique without the external sensing resistor can sense the current flowing through LEDs during the turning on of the N-type power MOSFET, as well as provide adaptive off-time depending on the input voltage and the numbers of LED, to obtain an accurate LED current. Experimental results show the inductor current ripple is kept within ±15% of the DC current. As a result, line regulation is guaranteed in this proposed design. This driver circuit design was simulated and fabricated in TSMC 0.25□m embedded high voltage 5V/40V CMOS technology. The circuit operates from an input supply between 8V and 40V and provides an externally adjustable output current of up to 1A.