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最近发现串连的lcd背光驱动会叫
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Why noise output from choke?
Why the output choke got noise sound when the 3D mark running?
The reason is the loading change frequency between 50Hzand 20KHz,
The core and wire of coke will vibrate by loading change frequency,the noise of chokewill follow the frequency , and the loading change level will change the noise dB.
If the vibration frequency out of this range or the noise less 10 dB, we can't hear it.
Many M/B gotsame result,
Whenvibration noisehappen on transientorloading change only,
And thethermalof choke never getting hot , it's normal.
On the static load, the chokeshould silence.
If on the static load , the choke got noise and also getting hot, that's abnormal.
Poor the gain of feedback and poor transient response also can reduce the noise.
Like slow down the switching frequency , reduce the gain of compensation, or use slowly response time, it will help to reduce the noise. But the change will impactto the transient result.
For example : when the loading be changed by 50A/us, the output chokefollow by 10A/us, it's need 5 us togotthe change.
If output can follow fast than 50A/us, than the change time will short and the vibration will heavy , the noise dB will increase .
Increase switching frequency, change the vibration frequencysome times reduce the noise, But the change will impactto the thermal of Upper Mosfet.
Summary:
The choke silence on static load, thermal stable on static and loading change, getting noise from loading transient, It's mean normal. Nothing changerecommend.
If the noise is not acceptable by customer, a little lower switching frequency will smaller impact to transient and improve the thermal of high sideMosfet.
But the change doesn't mean the noise will be gone, some loading c frequency change or heavy current change slew rate, the noise will possible happen again.
Why the output choke got noise sound when the 3D mark running?
The reason is the loading change frequency between 50Hzand 20KHz,
The core and wire of coke will vibrate by loading change frequency,the noise of chokewill follow the frequency , and the loading change level will change the noise dB.
If the vibration frequency out of this range or the noise less 10 dB, we can't hear it.
Many M/B gotsame result,
Whenvibration noisehappen on transientorloading change only,
And thethermalof choke never getting hot , it's normal.
On the static load, the chokeshould silence.
If on the static load , the choke got noise and also getting hot, that's abnormal.
Poor the gain of feedback and poor transient response also can reduce the noise.
Like slow down the switching frequency , reduce the gain of compensation, or use slowly response time, it will help to reduce the noise. But the change will impactto the transient result.
For example : when the loading be changed by 50A/us, the output chokefollow by 10A/us, it's need 5 us togotthe change.
If output can follow fast than 50A/us, than the change time will short and the vibration will heavy , the noise dB will increase .
Increase switching frequency, change the vibration frequencysome times reduce the noise, But the change will impactto the thermal of Upper Mosfet.
Summary:
The choke silence on static load, thermal stable on static and loading change, getting noise from loading transient, It's mean normal. Nothing changerecommend.
If the noise is not acceptable by customer, a little lower switching frequency will smaller impact to transient and improve the thermal of high sideMosfet.
But the change doesn't mean the noise will be gone, some loading c frequency change or heavy current change slew rate, the noise will possible happen again.
对于比较高的控制频率，我想应该是通过FB电路实现PWM方式。我们使用的mps的DC-DC regulator,内部采用比较器进行控制，好像没有看到这方面的要求。
babybird，你们用的器件型号是什么？所指的正常工作频率是哪部分的工作频率？能不能把内部工作原理大体地说一下呢？
1，如果用PWM对芯片的FB端进行控制，应该不会有吱吱的噪声；产生吱吱噪声的电路一般是用PWM控制芯片的EN端时会出现，且是输出电容发出的，可以换成耐压值高一点的电容或者改为钽电容解决；也可以调整PWM的频率到人耳听不到的范围。
2，另外一个原因是：有些翻盖手机设计时都有一个检测翻盖用的小磁铁，如果这个小磁铁放的位置在背光电路的电感附件，则会造成扬声器效应，也会发出噪声。
如果可以的话试试采用全封闭的电感，用于EL背光的那种
LED driver 是DC/DC，靠开关产生高频震荡来提升电压输出，做这个和做开关电源原理一样，后端匹配不良就产生自激
同意楼上的,这实质就是电源,出现那声音,主要就是电源滤波部分,试着调节电感和电容,调节时注意用视波器检测
我觉得和电感有关系
以后是站长提的问题，大家一定要踊跃回答啊，没事就给你加点RD币
把PWM波控制改为直流控制，就不会有这个问题了。
通常串联step-up DC/DC是boost,外部需要一个大的电感，而这种噪声，就是线圈高频运动效应产生，当此线芯震动频率与磁体结构空腔固有频率产生共震时，即噪音最大化成为自激。做过开关电源的都深有体会·！
由于BOOST DC/DC这种通过功率电感与MOS抬升电压输出的固有元件限制，就不可避免有开关噪声。这是其特性，不可能完全消除，只有最大可能通过改变其PWM频率或后端调节高频谐振匹配降低自激耦合
我们的也发生过，似乎和诸位说的不一样呢？我们改变了屏的刷新率后就消失了，这个是怎么回事呢？
这个声音是机械震动产生的!一般换了电容可以改变!是电感发出的.改变PWM的频率声音大小会不一样的
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