求教:LCD 背光调节方式

kaka198510

1>通过PWM调节boost的enable pin,达到调节背光亮度的目的.可能是效率不够高!
2>通过PWM调节boost的FB,去达到调节背光的目的.但是后面的调节线路,我不是很懂!求教!线路如下图:
! f1 T+ s! ^7 o% ?
* d* B0 `/ ]# HR4,Rdc,R3是如何选择的,目的是干啥呢?

jacklee_47pn

Using a Filtered PWM signal
1 h& @+ [0 p0 M* M( dAnother common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended application circuit is shown as Figure 3. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. The LED current can be calculated by the following Equation:

jacklee_47pn

也就是 PWM signal 控制亮度。 R_DC 和 C_DC 做濾波，R3 和 R4 控制 PWM 和 FB 的比例。

jacklee_47pn

你的問題與這個 https://www.eda365.com/thread-86786-1-1.html 問題類似，18樓有 TI 芯片資料和EXCEL計算方式。你的 RT9293 也可以像那樣建立快速的計算表格。

kaka198510

谢谢了  版主!

zgq800712

这个我好像回过帖子的，没有人看。
2 J& O, M) U4 }, I6 c3 yhttps://www.eda365.com/thread-86786-2-3.html  
21楼

kaka198510

谢谢,大家了!我几经搞清楚了