【作者】 陈英；

【导师】 冯全源；

【作者基本信息】 西南交通大学 ， 交通信息工程及控制， 2010， 硕士

【摘要】 新一代光源—白光LED在如今的照明领域中拥有巨大的潜力。相比于传统光源,LED的优势明显,例如高发光效率、高响应速度、低功耗、小尺寸、长寿命等优点。LED广泛应用于背光、闪光灯、屏幕显示、信号指示及交通工具等各个方面。由于应用中对白光LED亮度均匀性的要求,以及白光LED自身的正向导通电压大、电学参数离散性大、容易受温度影响等特点,需要LED驱动电路来保证白光LED的正常工作。白光LED的迅速发展同时也推动了LED驱动电路的前进,如今,LED驱动集成电路已成为电源管理的重要组成部分。本文首先讨论了LED驱动的发展。目前,驱动LED的方式主要有恒压驱动和恒流驱动两种形式,由于LED的发光亮度主要受其驱动电流的影响,而恒流驱动方式可以消除温度和工艺等因素引起的正向电压变化所导致的电流变化,保证恒定的LED亮度,所以恒流驱动是非常普遍的方式。本文就着手于设计一种LED恒流驱动模式。关于恒流驱动模式,本文讨论了线性调整型、电容式开关型和电感式开关型三种驱动方案,通过对各种恒流调制原理的分析,指出滞环电流控制是一种具有自稳定性、系统结构简单的恒流调制方式。本文设计了一款降压型LED恒流驱动芯片的滞环控制电路。该芯片采用高边电流检测方案,运用滞环电流控制方法对驱动电流进行滞环控制,从而获得恒定的平均驱动电流。设计采用简单的设计理念实现恒流驱动,不需要复杂的电路分析,能实现精确的电流控制,且自身具有稳定性。内部电路主要模块包括电压调整器、带隙基准、两级折叠式运算放大器、比较器、输出驱动电路和功率开关管等。本文对于各个模块进行具体的设计与仿真,最后对整体电路的工作过程进行了分析和仿真,同时为确保设计合理性对系统的各种关键性能进行了验证,结果表明,该电路满足设计要求。芯片采用5V/18V/40V CDMOS工艺研制,电源电压范围为4.5V-28V,工作温度-40℃-+125℃,可为LED提供350mA左右驱动电流,通过调节外部检测电阻,可调节恒定LED驱动电流。外部提供DIM信号,通过DIM的占空比来调节LED的亮度。Hspice仿真结果显示：LED驱动电流为滞环变化的三角波,恒流精度约为6.3%。更多还原

【Abstract】 In the lighting field, The new-generation photosourcen White-Light LED has great market potentials. Compared with the traditional lighting sources, the advantages of LEDs are obvious, such as high luminous efficiency, high response speed,low power consumption, small size, long life, and so on. LEDs have been widely applied to back lighting, flashlamp, screen display, the signal direction and transportation means. Considering characteristics of white LEDs and necessity of uniform brightness, white LEDs need to be driven by special power management circuits.The boom of white LED greatly promotes the development of integrated circuits for driving LED, which begins to play an important role in the market of power management.In the paper, the development of LED driving is introduced at first. At present, there are two driving mode for LED-constant voltage driving and constant current driving. Luminance is mainly controlled by LED driving current, but the constant current driving can eliminate the change of current in the LEDs caused by the voltage change with the changes of temperature and process, so that we can achieve a constant brightness of the LED and the control mode of constant-current driving is a common way. LED-constant current driving is presented in this paper.As for the control mode of constant-current driving, the hysteresis-current control technique has advantages of simple structure, Self-stabilization and practicality. Three kinds of methods for driving LED(linear regulation mode, capacitor switching mode, inductor switching mode) are discussed in this paper. Though the analysis of several modes of constant-current control, it is concluded that the hysteresis-current control mode is very suitable for driving LED due to its self-stability and simplicity.A chip which is used in the buck application to drive white LED with a constant current is proposed in this paper. Using high-side current sensing topology, it controls the driving current for LED to be averagely constant through hysteresis-current control technique. The chip realizes constant-current driving without complicated circuit design, provides the accurate control of current and self stabilization. The chip is mainly composed of a voltage regulator, a bandgap reference, a two-stage folded operational amplifier, a comparator, an output driving circuit and a power MOSFET.All the sub-circuit are designed and simulated, at last the synthetic circuit is simulated, the key parameters of the synthetic circuit are verified by Hspice, and the results of simulation meet the function requirement. It is designed and fabricated with a 0.5um 5V/18V/40V CDMOS process with input voltage ranged from 4.5V to 28V, with working temperature ranged from-40℃to+125℃. The chip can provide a driving current of 350mA for LED, it can provide an adjustable driving current through adjusting the outside current-sensing resistor. The duty cycle of the signal DIM can be adjusted to realize lightness regulation of LED. Hspice shows that LED driving current is hysteresis, and the Precision of constant current can be controlled within the range of 6.3%.更多还原