X capacitance analysis and recommendation

C1, L1, and C2 form a double π-type filter network. C2 (X-capacitor), C3, and C4 (Y-capacitor) are safety capacitors. They both suppress the electromagnetic noise and clutter signals of the input power supply, and also prevent power supply. The high-frequency noise generated by itself interferes with the power grid. In general, the X capacitor uses a polypropylene film capacitor. This type of capacitor has a large size, but it allows a large current to be instantaneously charged and discharged, and its internal resistance is relatively small.

In contrast, the common capacitor ripple current is lower and the dynamic internal resistance is higher. Therefore, using an ordinary capacitor instead of the X capacitor, in addition to the capacitor withstand voltage can not meet the standard, the ripple current indicator is difficult to meet the requirements.