The use of feedthrough capacitors in actual engineering, the frequency of electromagnetic noise to be filtered is often as high as hundreds of MHz, or even more than 1 GHz. For such high-frequency electromagnetic noise, feedthrough capacitors must be used to effectively filter out.
The reason why ordinary capacitors cannot effectively filter high frequency noise is due to two reasons:
1. It is the capacitor lead inductance that causes capacitor resonance, which presents a large impedance to high-frequency signals, which weakens the bypass effect of high-frequency signals;
2. It is the parasitic capacitance between the wires that couples high-frequency signals, which reduces the filtering effect. The reason why the through-core capacitor can effectively filter high-frequency noise is because the through-core capacitor not only has no lead inductance, which causes the capacitor resonance frequency to be too low. In addition, the through-core capacitor can be directly installed on the metal panel, and the metal panel can be used for high-frequency isolation.
The use of feedthrough capacitors the problem to pay attention to is the installation problem. The biggest weakness of the through-core capacitor is that it is afraid of high temperature and temperature impact, which causes great difficulties when welding the through-core capacitor to the metal panel. Many capacitors are damaged during the welding process. Especially when a large number of through-core capacitors need to be installed on the panel, as long as one is damaged, it is difficult to repair, because when the damaged capacitor is removed, other nearby capacitors will be damaged. With the increase in the complexity of electronic equipment, there are more and more cases of mixed installation of strong and weak electric and digital logic circuits inside the equipment, and mutual disturbance between circuit modules has become a serious problem. One of the methods to solve the mutual disturbance of such circuit modules is to isolate circuits of different natures with metal isolation cabins. But all the wires passing through the isolation cabin must pass through the core capacitor, otherwise it will cause isolation failure.
