摘要
作为新兴的固态光源，白光LED具有无污染，高效率，使用寿命长等优点，在现代照明系统中拥有广泛的应用前景。由于白光LED的颜色和亮度受正向电流及温度的影响显著，对其驱动芯片的性能提出了很高的要求。同时，诸如汽车电子照明系统及工业控制系统等应用场合具有输入电压高，变化范围大等特点，更给系统的设计带来难度。
针对上述应用，论文给出一种白光LED驱动芯片的设计方案。特点是采用了BOOST型DC／DC变换电路，峰值电流的控制模式，使负载LED上的电流保持恒定。为降低成本，提高芯片的适应性，方案摒弃了芯片内集成功率MOS管和开关二极管的做法，使之可根据驱动电流的大小灵活选择合适的外围器件。为解决串联连接的LED数目不定，导致驱动电压与输入电压有可能不匹配的问题，提出的系统可根据需要工作于两种不同工作模式下——恒流模式和恒流／恒压模式。为方便数字控制，防止发光颜色的偏差，针对驱动芯片的技术关键——白光LED的亮度调节，设计采用了PWM调光方式，并同时具备模拟调光的功能，以扩展调光范围。所完成的驱动芯片输入电压范围3V-36V，输出可以驱动1个到10个LED，工作频率最高为1MHz。
论文重点设计了环路控制中的主要电路模块，如误差放大器，振荡器以及电压调整器，斜坡补偿电路等模块。其中，采用两级带隙基准的结构解决了高输入电压与精密基准电压之间的矛盾。电路模块的成功设计保证了系统整体性能的实现。此外，芯片还具备软启动，过压保护，过温保护等功能以及关断工作模式，以保护系统不受到过压、过温的损害，方便外围系统对其控制，并降低了系统的功耗。
所有设计均在1.5um BiCMOS工艺下完成，利用Cadence Spectre工具软件仿真的结果表明，各电路模块工作正常，预期的系统功能均已圆满实现。
As a hopeful solid state lighting source, white LED has some outstanding advantages like non-pollution, high efficient, long life, etc. and thus it is widely adopted by modern electronic lighting system. Because its color and brightness are seriously affected by the forward current, the high performance driver integrated circuits (IC) are demanded. Besides, some rigorous applications such as industrial control system or automotive lighting system bring more difficulties to the design of drivers due to their high input voltage and wide input voltage range. Therefore, a lot of efforts were put into the research on these drivers.
To meet the requirements of such drivers, this thesis proposed a solution of white LED driver, in which the BOOST topology and peak current control mode were employed to keep LED load current constant. To provide the maximum application flexibility of driver and reduce its cost, a solution with off-chip power MOS transistors and off-chip switch diodes was chosen. The driving current can be fixed by system and users could conveniently select periphery elements according to their requirements. Since the load LEDs are in series, the output voltage depends on the number of LEDs, and the output voltage could be higher or lower than the input voltage. To meet the different requirements requested by different operation states, one solution which provides both constant current mode and constant current/constant voltage mode was introduced. Considering that one of the important functions of LED driver chip is dimming, PWM dimming was employed to keep the true color, and to facilitate digital use. Meanwhile, the analog dimming was reserved in this design to extend dimming range. The input voltage of the chip ranges from 3 V to 36V. The number of LEDs that could be driven is 1 to 10. And the operating frequency up to 1MHz could be set by an external resistor.
The circuit design of main modules in the driver such as error amplifier, oscillator, ramp compensation circuits and voltage regulator were completed. To get precise voltage reference under very high input voltage, the structure with two stages bandgap voltage reference was employed. All circuit modules were carefully
designed to ensure the high performances of the system. The circuits of soft-start, over voltage protection, over temperature protection and system shutdown were integrated into the chip to protect it from damage and make it convenient to use.
The LED driver presented in this paper was designed in 1.5um BiCMOS process, and simulated with Cadence Spectre. Simulation results show that it works well and all expected functions were achieved successfully..
引文
[1] 程江华 谢剑斌等 白光LED电源驱动电路的设计与实现《电子技术》，51页，2005．8
[2] Keith Szolusha汽车照明电源的LED驱动器《电子与电脑》，93页，2006．4
[3] Doug Varghn白光LED驱动方案《电子产品世界》，50页，2002．6
[4] Robert Mammano Switching Power Supply Topology Voltage Mode vs. Current Mode, UNITRODE Design note, DN-62, Page 10
[5] E.M.Cherry Common-base-input operational amplifiers, IEE Proc.-Circuits Device Syst., Vol. 152, No. 6, December 2005
[6] 陈友福，李平等，一种新型的BiCMOS带隙基准电压源《微电子学》，第36卷第3期，2006年6月
[7] Hassan Pooya Forghani-zadeh, Gabriel A. Rincon-Mora. Current-Sensing Techniques for DC-DC Converters.0-7803-7523-8/02 2002 IEEE
[8] Tim Regan. Current Sense Circuit Collection. LINEAR Application Note 105. December 2005
[9] High Side Current Sensing. Electronic Engineering Times-Asia. March 16-31, 2006
[10] 邹雪成 开关电源芯片中过温保护技术的研究与实现，《微电子学与计算机》，2006年第23卷第7期
[11] 谭春玲 一种BiCMOS过温保护电路，《电子器件》，第29卷第2期，2006年6月
[12] M.H.Nagel, M.J.Fonderie, Integrated 1V Thermal Shutdown Circuit, 《ELECREONIC LETTERS》,Vol.28 No. 10 7th May 1992
[13] Pedro M. Alicea-Morales, Carlos J. Ortiz-Vollanueva, Design of an Adjustable, Low Voltage,Low Dropout Regulator, Proceedings of the Fifth IEEE International Caracas Conference on Devices, Circuits and Systems, Dominican Republic, Nov.3-5, 2004
[14] Sai Kit Lau, Ka Nang Leung, Analysis of Low-Dropout Regulator Topologies for Low-Voltage Regulation 0-7803-7749-4/03, 2003 IEEE
[15] 赵双龙，吴晓波，严晓浪．低压差电压调整器中的热保护电路设计 微电子学与计算机 2006年23卷第8期
[16] 杨锦文，冯全源．基于嵌入式密勒补偿技术的LDO放大器设计 微电子学与计算机 2006年第23卷第3期
[17] 陈晓飞，邹雪城，刘三清，张宾．一种新颖的BiCMOS高精度LDO线性稳压电路微电子学2006年2月第36卷第1期
[18] Hassan Pooya Forghani-zadeh, Gabriel A. Rincon-Mora. Current-Sensing Techniques for DC-DC Converters.0-7803-7523-8/02 2002 IEEE
[19] Tim Regan. Current Sense Circuit Collection. LINEAR Application Note 105. December 2005
[20] High Side Current Sensing. Electronic Engineering Times-Asia. March 16-31, 2006
[21] Jiann-Jong Chen, Juing-Huei Su, Hung-Yih Lin, Chung-Chieh Chang, Yu Lee, Tzu-Chiang Chen, Integrated Current Sensing Circuit Suitable for Step-Down DC-DC Converters Annul IEEE Power Elecfronics Specialisfs Conference
[22] Armin Tajalli, Mojtaba Atarodi, Abbas Khodaverdi, Farzard Sahandi Esfanjani, "Design and optimize of a high PSRR CMOS bandgap voltage reference", 0-7803-8251-X/04 IEEE (2004)
[23] Cheung Fai, Philip K.T.Mok On-chip Current Sense Technique For CMOS Monolithic Switch-Mode Power Converter 2002 IEEE
[24] M.E Brinson and D.J. Faulkner Selection of operational amplifiers for power supply current sensing applications Electronics Letters Online No: 19951069 1998 IEEE
[25] 乔飞，杨华中，罗嵘，汪葱宽工作电压范围单电源CMOS误差放大器微电子学2004．2
[26] Jian Zhou, Jin Liu On the Measurement of Common-Mode Rejection Ratio IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS VOL. 52, NO. 1, JANUARY 2005
[27] Song Ying, Lu Wenggao, Chen Zhongjian, Gao Jun, Tang Ju, Ji Liliu, "A Precise Compensated Bandgap Reference without Resistor", 7th International conference on Solid-State and Intergrated Circuits October 18-21 Beijing (2004)
[28] Rajiashi Paul, Amit Patra, Shailendra Baranwal, Kaushik, "Design of Second-Order Sub-Badgap Mixed-Mode Voltage Reference", 18th Internationnal conference on VLSI Design(2005)