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LDO线性恒流型高亮度LED驱动的研究与设计

Research and Design of a Low Dropout Linear Current Regulative HB-LED Driver

【作者】 林映嫣

【导师】 张科峰;

【作者基本信息】 华中科技大学 , 微电子学与固体电子学, 2007, 硕士

【摘要】 高亮度LED(发光二极管)作为光源具有发光强度大、发光效率高、节能环保、寿命长等优点,被认为是21世纪最具发展潜力的新光源,广泛应用于汽车照明、显示器、相机用闪光灯、面板背光源、景光照明和室内装饰等照明领域。为了充分发挥高亮度LED的优势,良好的驱动是不可或缺的,世界知名半导体器件公司纷纷开发出各种新型高亮度LED驱动芯片以满足市场的需要,高亮度LED驱动芯片是目前电源管理芯片市场的研究热点。对于蓄电池供电的汽车照明等领域的高亮度LED,低压差线性恒流型LED驱动由于具有结构简单、电磁干扰(EMI)与噪声低、响应迅速、尺寸小及成本低等优点,是性价比较高的设计方案。论文主要讨论了一种高压、350mA、低压差线性恒流型高亮度LED驱动芯片的研究与设计。设计先按照芯片需完成的功能,确定系统的结构与电路划分,然后结合“自底向上”的原理图输入设计方法对部分电路进行设计,最后根据系统设计的框架对各电路进行协调设计,并进行芯片的整体性能验证。本文的研究重点在于低压差线性恒流型高亮度LED驱动芯片的总体设计与线性恒流型驱动的效率改进,详细介绍了芯片中带隙基准与稳压输出、误差放大器、过热保护等子电路的设计过程,并给出了相应的仿真结果和分析。在前面研究的基础上,采用Jazz 0.5μm BCD制造工艺完成了一款低压差线性恒流型高亮度LED驱动芯片的前端与后端设计。芯片后仿真结果表明,芯片可工作于汽车电子级宽输入电源电压范围(+6.3V~+32V)与宽温度范围(-40℃~+125℃);具有过热保护、过流保护、PWM亮度调节使能控制、204mV低电流检测基准等功能;在+12V电源电压下输出电流精度在±2.86%以内,实现典型值为0.5V的低压差设计;另外,对线性恒流型高亮度LED驱动的优化设计有效地提高了芯片效率。后仿真结果表明芯片的设计指标达到既定的要求。

【Abstract】 High Brightness LED as the most promising light source has many advantages, such as high luminous efficiency, high luminous intensity, economical and safety for environment, long life period etc. It is widely used in automotive illumination, display, the flash on cell-phone camera, back lighting of panel and other illuminating applications. The HB LED driver is indispensable, and become the star of power management research. Providing constant current is the major task. For its briefness, low noise and EMI, fast transient response, mini bulk and inexpensive, linear current regulator is well suited for illuminating fields using storage battery as power supply, such as automotive illumination. In this thesis, the research and design of a high voltage, 350 mA, LDO linear current regulative HB LED driver is demonstrated. According to the functions the IC should have, the structure and functional blocks of the system were determined, then the direct schematic design of some subcircuits had also been conducted in reference to other function-like circuits, using the“Bottom-to-up”methodology. Then, the whole chip simulation and verification were conducted to examine the matching between the design and the requirements of specification. The thesis put emphasis on the whole design of the chip and improvement on efficiency of the linear current regulator, especially on the design of some critical blocks, such as reference and voltage regulator block, error amplifier block and thermal protect block.On the basis of above research, a LDO linear current regulative HB LED driver is designed and fabricated in Jazz 0.5μm BCD process. Simulation results show that the chip can achieve±2.86% output current accuracy and 0.5V low-dropout voltage, and it features the functions of over temperature protection, over current limiting, PWM dimming at output current as well as low 204 mV current-sense reference. Besides, optimization design for the LED driver improved the efficiency effectively. The post simulation has proved that the circuit works very well and every electrical characteristic meets the specification of the data sheet which proves a successful design.

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