使用AMS1117-3.3和SPX1117M3-L-3-3对比，输入电压DC5.0V，负载10mA。

先看SPX1117M3-L-3-3的纹波

纹波很小。直接换一个AMS1117-3.3看看，

耳朵能听到有啸叫声，纹波还这么大。

然后又买了一次30个AMS1117-3.3，测试一样的效果。

求解，那里出了问题...  

我去，我在商城里面特地选了AP1117，也遇到啸叫了，输入输出电容10uF/22uF MLCC。当然可能和我前端用的ACDC太便宜有关系？或者和电容有关系？

这批是自己手工贴的电容，电容已经无法确定是X5R还是X7R的了，理论上应该是X7R。

我在另外一个案子上用TPS54331从24V转5V给同样一批1117供电就没啸叫的问题。没问题的这批是立创贴片的X7R电容，但是加了磁珠。

如下是AP1117的datasheet节选，里面说了可以用MLCC的：

Input Capacitors

To ensure stable operation, the input supply must be low impedance up to a frequency of a few MHz. This requires a closely placed input

decoupling capacitor of 4.7μF minimum. This can be either ceramic or solid tantalum. The ESR of this capacitor must be less than 0.5Ω.

Output Capacitor

The AP1117 also requires a closely placed output capacitor as part of the device frequency compensation. As part of its improved performance

over industry standard 1117, the AP1117 is suitable for use with MLCC (Multi-Layer Ceramic Chip) capacitors. A minimum output capacitor of

4.7μF ceramic X7R or 4.7μF solid tantalum is required. Aluminum electrolytic can be used but a minimum of 47μF is required. When using

Aluminum electrolytic it is still recommended to also use a 1μF MLCC in parallel. The ESR of the output capacitors must be less than 0.5Ω.

补充一下，我是楼上，我现在觉得也可能是ACDC的啸叫，还无法确定.....