环境光自适应 LED 驱动器
AMBIENTLIGHTADAPTIVELED-REF
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描述

The ambient light adaptive LED driver automatically adjusts display brightness for changing ambient light conditions, providing a more viewable display with better contrast. The design drives five series connected LEDs from an input voltage of 4.5V to 12V. The LED current is nominally 100mA and the output voltage is 15 to 20V.

The heart of the design is National’s PowerWise® LM3423 LED driver which has all the features needed to implement a boost converter with output current regulation and PWM dimming of the current. The LM3423 achieves output current regulation by sensing and appropriately adjusting the voltage across a resistor connected in series with the LED string.

Dimming or brightening the backlight of a display in response to ambient light condition can greatly increase the life of batteries in portable devices, and improves the visibility of the display under different viewing conditions. In this design a photodiode circuit is used to measure ambient light and provide a signal for dimming the LEDs.

PWM dimming is the preferred method of dimming because it allows the light’s color temperature to remain constant irrespective of its intensity. PWM dimming is done by keeping the amplitude of the LED current constant, but periodically turning the LED driver on and off, thus varying the LEDs’ average current and light intensity. The switching is at done at a low frequency, but one which is high enough for the human eye to sense only changes in the light’s average intensity. Linear dimming, where the amplitude of the current in the LEDs is modulated, is not suitable because the LEDs’ light color temperature is sensitive to the current’s amplitude.

The dimming range of the average LED current is from 20 to nearly 100% percent of its nominal value as ambient light conditions increase from dark to bright. To reduce power consumption and prolong battery life the output current is clamped to no more than 50% of the nominal value when the input (battery) voltage falls below a predetermined level.

特性
Inputs Outputs #1
VinMin=6V Vout1=20V
VinMax=12V Iout1=0.1A
  • 4.5-12V battery input voltage range 
  • 100mA Constant current LED at 15-20V 
  • High switching frequency 
  • High efficienty (85%) 
  • PWM LED dimming up to 25kHz 
  • LED brightness limited to less than 50% of maximum at low input voltage to prolong battery life 
  • LED brightness proportional to ambient light

 



  




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AMBIENTLIGHTADAPTIVELED-REF:
Ambient Light Adaptive LED Driver



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TI 器件 (5)

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器件型号 名称 产品系列 样片或购买 设计套件与评估模块
LM3423  用于恒流 LED 驱动器的 N 通道控制器  LED驱动器  样片或购买 查看设计套件与评估模块
LM3423-Q1  用于恒流 LED 驱动器的 N 通道控制器  LED驱动器  样片或购买 查看设计套件与评估模块
LM3424  具有热折回的恒流 N 通道控制器,用于驱动 LED  LED驱动器  样片或购买 查看设计套件与评估模块
LM3424-Q1  具有热折回的恒流 N 通道控制器,用于驱动 LED  LED驱动器  样片或购买 查看设计套件与评估模块
LMV431  低电压 (1.24V) 可调节精密并联稳压器  电压参考  样片或购买 查看设计套件与评估模块

符号和封装

型号 封装 | 引脚 CAD File (.bxl) STEP Model (.stp)
LM3423 下载 下载
LM3423-Q1 下载
LM3424 下载 下载
LM3424-Q1 下载
LMV431 下载 下载
下载 下载

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步骤 2: 从 CAD.bxl 文件表中下载符号和封装。


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用户指南 (1)
标题 类型 大小 (KB) 日期 下载最新英文版本
PDF 578 2012年 1月 27日
设计文件 (1)
标题 类型 大小 (KB) 日期 下载最新英文版本
ZIP 123 2012年 1月 27日

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