基于恒流架构的Boost型LED背光驱动芯片XD1430的设计

发布时间：2018-06-22 07:50

本文选题：白光LED + 峰值电流模　；参考：《西安电子科技大学》2014年硕士论文

【摘要】：近年来,随着技术的不断发展,白光LED的功耗逐渐降低,亮度逐渐升高,成为LCD背光源驱动的主流背光源。本文结合白光LED的发光原理以及驱动特性,设计了一款基于恒流架构的Boost型6路白光LED背光驱动器,其可以作为大型LCD背光源驱动。单个白光LED的发光亮度有限,为支持大型LCD背光源应用需要多个白光LED的共同作用,并联支路太多导致输出电流过大,每一路串联个数太多导致输出电压过高,综合考虑这两方面的因素,论文中白光LED采用串并联结合的混合连接方式,最多并联通路为6路,最高串联个数可多达12个。而且由于白光LED正常工作时两端的电压比较高(3.4V左右),所以输出电压相对较高,本文输入电压的指标要求4.5V~28V,综合考虑设计要求,需要采用升压Boost转换器。本文首先介绍了Boost转换器的基本原理,为分析其交流特性,利用线性元件替换非线性的开关元件对其建模。然后对反馈控制方式峰值电流模进行了详细的阐述和探讨,为保证反馈环路稳定,考虑斜坡补偿的影响后对其进行精确的交流小信号建模,计算环路的传输函数。在LED电流驱动架构的选择上,考虑到流过白光LED的电流对其发光亮度的决定关系,以及恒压架构不容易对LED电流进行调节两方面的因素,本文选择恒流源的结构来驱动白光LED。利用峰值电流模升压型拓扑结构的反馈环路保证LED电流源正常工作以及稳定恒流源上的电压。LCD的背光源要求其驱动芯片可以自动调节发光亮度。本论文设计了模拟调光和PWM调光两种形式,使白光LED电流在0~60mA范围内可调。模拟调光是指LED电流跟随直流输入电平变化,主要应用于对噪声要求高、对发光质量要求不是很高的场合。PWM调光是指LED电流以PWM开关信号方式输出,占空比改变平均输出电流大小,主要应用于高亮度以及对噪声度要求不高的场合,这两种调光方式可以满足大多数LCD背光应用要求。为提高LED驱动电源的效率,LED电流不同时,反馈环路将恒流源的电压恒定为不同的值,电流低时,恒流源上的电压比较低,电流高时,恒流源上的电压比较高。在前三章对驱动芯片环路架构原理、稳定性以及白光LED恒流源架构的分析基础上,第四章详细设计了驱动芯片中的五个典型子电路模块,包括PWM调光信号产生电路、LED开路以及短路到地保护模块、误差放大器模块、最小反馈电压检测模块以及电感电流采样模块。在芯片整体功能分析以及子电路设计基础上,本芯片基于0.35μm BCD工艺,利用Hspice、Cadence等EDA仿真软件对子模块设计电路进行仿真验证,在仿真过程中,综合考虑电源、温度以及工艺对设计电路的影响,最后对整体应用电路也进行了功能仿真验证,仿真结果表明,电路的各项指标均能达到设计要求,同时可实现所需功能。
[Abstract]:In recent years, with the continuous development of technology, the power consumption of white LED gradually decreased, brightness gradually increased, and become the mainstream backlight driven by LCD backlight. Based on the principle and driving characteristics of white LED, a boost six-channel backlight driver based on constant current architecture is designed, which can be used as backlight driver for large LCD. The brightness of a single white LED is limited. In order to support the application of large LCD backlight, it needs the common action of multiple white LED. Too many parallel branches cause the output current to be too large, and too many series each lead to high output voltage. Considering these two factors, the white LED in this paper adopts the hybrid connection mode of series-parallel connection, the maximum parallel path is 6 channels, and the maximum number of series is up to 12. Because the voltage at both ends of white LED is relatively high (about 3.4 V) when it works normally, the output voltage is relatively high. The input voltage requirement of this paper is 4.5V ~ (28) V, considering the design requirements, boost converter is needed. In this paper, the basic principle of boost converter is introduced. In order to analyze its AC characteristics, linear elements are used to replace nonlinear switching elements to model it. Then, the peak current mode of feedback control is described and discussed in detail. In order to ensure the stability of feedback loop, considering the influence of slope compensation, the accurate AC small-signal modeling is carried out, and the transmission function of loop is calculated. In the selection of LED current drive architecture, considering the relationship between the current passing through the white LED and its luminance, and the fact that the constant voltage structure is not easy to adjust the LED current, this paper chooses the structure of the constant current source to drive the white LED. The feedback loop of the peak current mode boost topology is used to ensure the LED current source to work normally and the backlight of the voltage. LCD on the steady current source requires that the driving chip can automatically adjust the luminance of the LED. In this paper, analog dimming and PWM dimming are designed to make white LED current adjustable in 0~60mA range. Analog dimming means that LED current changes with DC input level, which is mainly used in occasions with high noise requirement and low luminous quality. PWM dimming means that LED current is output by PWM switch signal. The duty cycle changes the average output current, which is mainly used in the cases with high brightness and low noise. These two dimming methods can meet the requirements of most LCD backlight applications. In order to improve the efficiency of LED drive power supply, the feedback loop keeps the constant current source voltage constant to different values. When the current is low, the voltage on the constant current source is relatively low, and the voltage on the constant current source is higher when the current is high. On the basis of analyzing the structure principle, stability and constant current source architecture of white LED in the first three chapters, five typical sub-circuit modules are designed in detail in the fourth chapter. It includes PWM dimming signal generating circuit, LED open circuit and short circuit to ground protection module, error amplifier module, minimum feedback voltage detection module and inductance current sampling module. On the basis of the whole function analysis and sub-circuit design of the chip, this chip is based on 0.35 渭 m BCD technology. The circuit is simulated and verified by EDA simulation software such as HspiceCad Cadence. In the simulation process, the power supply is considered synthetically. Finally, the effect of temperature and process on the design circuit is verified by functional simulation. The simulation results show that all the parameters of the circuit can meet the design requirements, and the required functions can be achieved at the same time.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46;TN312.8

【相似文献】