Is increasingly used in the output capacitance.
3, so with laminated direction (
The vertical direction (
, i. e. , parallel to the circuit board can also occur in the direction of the scale, as a result, the circuit board surface vibration and can hear the sound.
Although the capacitor
and the amplitude of circuit board is only 1 PM ~ 1 nm, but vibration has been large enough to we can hear voice, will hear the sound of the similar 'ji'.
Terms: poisson's ratio is refers to the material in a one-way tensile or compressive, transverse normal strain and axial strain is the ratio of the absolute value of, also called the poisson ratio, it reflects the elastic constants of the lateral deformation of the material.
Therefore, inhibition of capacitance noise are the main measures of inhibition or offset PCB deformation.
For example, can cause the noise of the capacitance on the same side, placed at different angles.
Or on both sides, it is to put;
Also, can choose the capacitor with stents, of course, it would increase costs, as shown in figure 3.
Above by inhibiting the PCB deformation way to deal with the problem capacitance squealing take temporary solution not effect a permanent cure, as far as possible to get rid of the causes of noise from the source.
In fact, the capacitance caused by the noise of the reason is very simple, must be loaded on the capacitor is the human ear can hear an alternating current (
此时率为20 hz ~ 20 khz)
Therefore, the analysis of the basic idea is as follows: first, roughly search capacitance is screaming with ears that an area;
Then, using the oscilloscope screen suspicious voltage signal, as shown in figure 4 lists some once capacitance caused by the noise voltage signal, for your reference.
4 khz # # 6。
3千赫# # 4。
# 3 KHZ, light load model in figure 4.
Once capacitance caused by the noise voltage signal by summing up the related case, capacitance of the noise is most happened in light load mode.
According to its reason, because the chip in light load mode usually into efficient mode.
As two hundred microamps)
At work, so that the energy generally is not enough to cause capacitance of the noise.
However, if the light load model (
With Normal PWM mode (
There are some circuit especially the low cost of simple circuit, software have no way to set the PWM mode, unfortunately capacitance mega event happened again, can try the following methods: 1, change the value of capacitance, even try different manufacturers or different types of capacitors;
, this is no way;
3, 'redundant' capacitance can also cause the loop is not stable, lead to the noise, can try to remove some 'nice-to-have' capacitance;
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