應用於發光二極體驅動電路之電流控制式直流-直流升壓電壓電源轉換

Abstract

傳統液晶顯示器主要以冷陰極螢光燈管所產生之光源來做為背光模組。然而隨著近年來發光二極體之製程技術進步，其優點日趨明顯，像是高色彩飽和度、較長使用壽命和無汞環保材料。因此越來越多技術傾向以發光二極體取代傳統冷陰極螢光燈管來達到高品質顯示器的市場需求。 目前在市面上有兩種直流對直流電壓轉換器提供發光二極體電壓。一種是無電感元件的電荷幫浦設計，另一種是含電感元件的切換式升壓直流對直流電源轉換器。其中電荷幫浦費用較低且電磁干擾小，然而和切換式升壓直流對直流電源轉換器相比，其效率會較差且輸出電流負載能力較弱。在面板的應用上，背光源通常需要上百顆發光二極體來提供光源，因此若能選擇效率佳且負載能力好之電源轉換器將可降低系統成本。所以切換式升壓電源轉換器之高效率與高負載能力適用於此應用。 本篇論文中提出應用於發光二極體驅動電路之電流控制式直流-直流升壓電源轉換電路設計，其輸入電壓為12V，輸出電壓為48V。其中回授控制電路是以脈波寬度調變方式實現，而其控制訊號傳輸方式為電流傳輸，此方式雖會造成系統靜態誤差變大但卻可以得到較佳的動態反應能力。回授控制電路之電源電壓源範圍為2.5伏特到3.6伏特。在負載電流為300毫安培時可達最佳效率92%。本論文之設計使用UMC 0.35um嵌入高壓3.3V/18V 2P5M CMOS製程技術進模擬與製作。

In the past, the backlight module for liquid crystal displays (LCD) consisted mainly of cold cathode fluorescent lamp (CCFL). However, with the greatly improving technology of light emitting diode (LED) process, the benefit for LED backlight is more and more obviously such as high color saturation, longer product life and none hydrargyrum. Thus, people are trying to replace CCFL to RGB LED to reach the high quality images in displays targeted for market. Two most popular approaches for LED driver implementation are an inductor-less charge pump converter and an inductor-based converter. Although the cost and EMI problem of a charge pump is low, the load ability and efficiency is poor compared to those of a switching regulator. In the application of high brightness LED driver, the high power characteristics are needed, since the number of LEDs for backlight implementation is above hundreds. The highly efficient voltage regulators are needed for energy transform, because of low power consumption in converters. Moreover, owing to driving a large number of LEDs in one controller, the cost of the system is reduced. This thesis presents a current domain DC-DC boost converter for LED application with 12V input voltage and 48V output voltage. The boost voltage regulator utilizes a pulse width modulation (PWM) current programmed control method, which transfers the control signal in current domain to improve the transient response. The disadvantage of this method is big static error. The supply voltage of the controller is in the range from 2.5V to 3.6V. The best efficiency of the converter is 92% at 300mA load current. This converter design is simulated and fabricated in UMC 0.35□m embedded high voltage 3.3V/18V CMOS technology.