The role of ceramic capacitors
2021 12 21 133910

Introduction to the role of ceramic capacitors
1. Filtering function: In the power circuit, the rectifier circuit turns AC into pulsating DC, and a larger capacity electrolytic capacitor is connected after the rectifier circuit, using its charge and discharge characteristics,
The rectified pulsating DC voltage becomes a relatively stable DC voltage.
In practice, in order to prevent the power supply voltage of each part of the circuit from changing due to load changes, electrolytic capacitors of tens to hundreds of microfarads are generally connected to the output end of the power supply and the power input end of the load.
Since large-capacity electrolytic capacitors generally have a certain inductance and cannot effectively filter out high-frequency and pulse interference signals, a capacitor with a capacity of 0.001–0.lpF is connected in parallel at both ends.
To filter out high frequency and pulse interference.

2. Coupling effect: In the process of low-frequency signal transmission and amplification, in order to prevent the static operating points of the front and rear two-stage circuits from interacting with each other, capacitor coupling is often used.
In order to prevent excessive loss of low-frequency components in the rhyme of the signal, electrolytic capacitors with larger capacity are generally used.
The materials of the two capacitors are different. Ceramic capacitors have no polarity, while electrolytic capacitors have polarity. The capacitance of ceramic capacitors is generally small, and the capacitance of electrolytic capacitors can be made large.
In addition, the purpose of the two is also different. Ceramic capacitors are generally used for signal source filtering, while electrolytic capacitors are generally used for power supply parts.
The positive electrode of the electrolytic capacitor is rolled into a tube with aluminum tape and placed in an aluminum case. This manufacturing method has a large capacity and also produces many defects, one of which is that the equivalent inductance of the electrolytic capacitor is relatively large.
Ceramic chip capacitors are capacitors with a “plate” structure. In simple terms, they are two parallel metal plates leading out of two legs, and the middle is separated by an insulating material to form a capacitor.
This structure has a small electric capacity, but a stable capacity and a small equivalent inductance. In what occasions a component is used, the equivalent inductance is an important parameter.

It can be seen from the above that the equivalent inductance of electrolytic capacitors is relatively large, which determines that it cannot be used in high-frequency applications, because the higher the frequency, the more obvious the effect of inductance.
The maximum frequency that electrolytic capacitors can apply is generally around 500KHz, so electrolytic capacitors are suitable for use in low-frequency filter circuits.
The equivalent inductance of the ceramic capacitor is small, so it can be used in high-frequency applications, and the operating frequency can reach more than one hundred megabytes, so it is mainly used in high-frequency filter circuits.
A typical application is the combination of the two. We can see that many power output terminals use an electrolytic and a ceramic capacitor in parallel, which is to let them “match the high and low” to achieve a better filtering effect.
Because the equivalent inductance of the large capacitor is too large, the decoupling effect on the high-frequency interference signal is too small.
After connecting small-capacity ceramic capacitors in parallel, since the equivalent inductance of the ceramic capacitors is very small, the high-frequency interference current will be short-circuited to the ground by the small capacitors, thereby decoupling the high-frequency interference of the power supply.