The ceramic capacitors used in the field of electronics are required to have the characteristics of small size, high resistance and good frequency.With the advancement of materials, electrode and manufacturing technology, high-voltage ceramic capacitors have gained a long-term development and have been widely used. The ceramic capacitors have become one of the indispensable components of big-power and high-voltage electrical products.
The capacitor ceramic (Barium titanate titanium monoxide) with high dielectric constant is extruded into a circular tube, a disc or a disc as the medium, and the silver is plated on the ceramic as an electrode by the sintering method. Capacitors with a small positive capacitance temperature coefficient are used in high-stability oscillation circuits as loop capacitors and pad capacitors. Low-frequency ceramic capacitors are only used as a bypass or used for blocking direct current in a loop circuit with low operating frequency or in some occasions where requires low stability and loss. It is inappropriate to use such capacitors in pulse circuits because they can easily be broken down by pulse voltage.
Easybom has conducted a series of investigation about the noise generated by the ceramic capacitors. Easybom has then found the reason why the ceramic capacitors generate noise and the specific ways to eliminate the noise.
The reasons why the ceramic capacitors generate noise analyzed by Easybom
- All insulating materials will deform under the pressure of the electric field, and this electrostrictive effect is proportional to the square of the electric field strength. Some insulating media also show a piezoelectric effect, that is, a linear displacement proportional to the intensity of an electric field. The piezoelectric effect is usually the main way for ceramic capacitors to generate noise.
- The non-linear insulating material in cheap small ceramic capacitors usually contains a large proportion of barium titanate, which produces piezoelectric effect at normal operating temperature. Therefore, these components will generate more noise than the capacitors with linear insulation materials. In the switching power supply, the capacitor in the clamp circuit with s large voltage deviation may generate audio noise.
- Generally, in order to suppress electromagnetic interference and reduce device voltage stress, switching power supplies generally use absorption circuits such as RC and RCD. High-voltage ceramic capacitors are often used for absorption capacitors, and high-voltage ceramic capacitors are made of non-linear dielectric barium titanate and other materials. The electrostrictive effect is relatively obvious. Under the action of the periodic peak voltage, the dielectric is constantly deformed, resulting in audio noise.
The specific ways summarized by Easybom to eliminate the noise
- Replace the high-voltage ceramic capacitor used in the absorption circuit with a polyester film capacitor with a small electrostrictive effect, which can basically eliminate the noise generated by the capacitor.
- To determine whether ceramic capacitors are the main noise source, you can replace them with capacitors with different insulators. Film capacitors are a good cost-effective alternative. However, attention should be paid to whether the replacement product can withstand repeated peak current and voltage stress.
- Another cost-competitive option is to replace the RCD clamp circuit with a Zener clamp circuit. The price of Zener clamp is comparable to that of RCD clamp, but it takes up much smaller space and is more efficient.
According the information given by Easybom, the noise generated by the ceramic capacitors can be solved using the ways mentioned above.