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Component Selection for EMI filter
Dec 20, 2018

Unlike the general filter, the capacitance in the typical structure of the EMI filter uses two subscript, which is called the differential mode capacitor, which is connected with the phase line or the midline and the ground, and is called the common-mode capacitor, and the subscript x and Y not only indicate its role in the filter circuit, but also indicate its security level in the filter circuit.

The safety performance of these two types of capacitors must be fully considered when designing or selecting filters, because it is directly related to the security performance of the filter network.

Selection of differential mode capacitors

Refers to the application of such an occasion: when the capacitor failure, will not lead to electrical breakdown phenomenon, will not endanger personal safety. In addition to bearing the voltage of the power phase line and the midline, it is also necessary to bear the peak voltage of various interference sources between the phase line and the midline. According to the worst case of differential mode capacitance application and the condition of power disconnect, the safety level of capacitor is divided into two levels, as specified in table 1. Therefore, when designing the filter, different safety levels of capacitors should be selected according to different application situations.