1. Internal structure and working principle
MLCC is Multilayer Ceramic Capacitor multilayer chip ceramic capacitor
The main parameters that determine the capacitance value:
Vacuum dielectric constant
Relative dielectric constant K: a constant related to the materials used in MLCC
Effective area S
Dielectric layer thickness d
Number of stacking layers N
Therefore, the larger the area and the more stacked layers, the higher the capacitance of the MLCC.
2. Causes of howling in MLCC
The MLCC is attached to the PCB. Since the dielectric layer of the MLCC is made of materials with a dielectric constant and has a certain piezoelectric effect, applying a voltage in one direction to the MLCC will cause it to produce a reverse piezoelectric effect. When alternating current is applied to the MLCC, the positive piezoelectric effect and the reverse piezoelectric effect are generated alternately, which will cause the PCB board to vibrate, and if the frequency is audible, it will whistle.
3.Solution
3.1MLCC arrangement
The same MLCC is arranged on the front and back of the PCB so that the vibrations can cancel each other out.
3.2MLCC material
MLCC with a smaller dielectric constant can reduce the deformation of the forward and reverse piezoelectric effects.
3.3MLCC structure
Since the reverse piezoelectric effect changes in parallel and PCB directions have a greater impact, the distance between electrodes can be shortened.
3.4MLCC installation method
A metal frame can be used to alleviate vibrations caused by the piezoelectric effect.
3.5 Adjust frequency
By adjusting the frequency, you can avoid the audible sound range of 20-20KHz.