What is Feedthrough Capacitor ?

The capacitance used in the EMI filter is generally a ceramic capacitor, which is also known as the feedthrough capacitance due to its physical structure. The feedthrough capacitor self-inductance is much smaller than ordinary capacitors, so the self-resonance frequency is very high. At the same time, the feedthrough design also effectively prevents the high-frequency signal from directly coupling from the input to the output. This combination of low-pass high resistance, in the 1GHz frequency range, provides excellent inhibition. The simplest feedthrough structure is one (type C) or two capacitors (type Pi) composed of the internal and external electrodes and ceramics. This capacitance has a capacity ranging from 10pF to 2 uF, with an operating voltage of up to 2,000 V D C. The tubular feedthrough capacitance does not produce significant self-resonance even at 10GHz frequency. The medium of the feedthrough capacitor is the ceramic medium, and the capacity of the ceramic capacitor will change with the ambient temperature, which will affect the filter cut-off rate of the filter. The rate of capacity and temperature change of the ceramic capacitance is determined by the ceramic medium itself. Therefore, it is very important to choose the appropriate ceramic dielectric.

What is an EMI Filter ?

The EMI mentioned here is an abbreviation of Electro Magnetic Interference and is an electromagnetic interference filter. It is a passive filter composed of inductors and capacitance. It allows low-frequency useful signals to pass smoothly, and it can inhibit high-frequency interference. The filter is a new type of component that has been popularized and applied in recent years. It can effectively inhibit the noise of the power grid, improve the anti-interference ability of electronic equipment and the reliability of the system, and can be widely used in electronic measuring instruments, computer room equipment, switching power supply, measurement and control system and other fields. Wear capacitor is a kind of three-end capacitor, but compared with the ordinary three-end capacitor, because it is directly installed on the metal panel, so its ground inductance is smaller, almost has the influence of lead inductance, in addition, its input and output by metal plate isolation, eliminate the high frequency coupling, the two characteristics determine the wear capacitor is close to the ideal capacitor filter effect.