The Concept of X and Y Capacitance

The technical parameters of capacitor in high frequency power supply mainly include capacitance, dielectric strength, loss Angle, stability and so on. 

Capacitors are divided into X capacitors and Y capacitors, as well as X capacitors between the live line and the neutral line.

Capacitor X is used in the power supply filter to filter the power supply, but also to filter the differential mode interference. The Y capacitor is used to eliminate common-mode interference. It is also a capacitor, which is usually used to jump over the two wires of the power line and the ground (L-E, N-E). Due to the limitation of leakage current, the capacitance value Y cannot be too large.

X and Y capacitors are safety capacitors. The difference is that capacitor X is connected at both ends of the input line to suppress interference in differential mode, while capacitor Y is connected between the input line and the ground line to suppress interference in common mode.

Generally, X capacitors are mainly polyester film capacitors with large ripple current resistance. This capacitor has a relatively large volume, but it also allows a large instantaneous charge and discharge current, and its internal resistance is small.  Capacitor Y is connected between the phase line and the ground line. Normally, the capacitor Y should be connected to a wire with more noise interference. X capacitance; Y capacitors have different functions when switching power supplies and are not interchangeable with each other.