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

The X capacitor adopts a plastic-encapsulated square high-voltage CBB capacitor. The CBB capacitor not only has better electrical performance, but also can effectively reduce the impact of high-frequency pulses on the switching power supply in parallel with the input end of the power supply.

Y capacitors---with high-voltage ceramics. The Y-type capacitor is connected between the phase wire and the ground wire. In order not to exceed the allowable leakage value of the ground wire defined by the relevant safety standards, the value of these capacitors is about a few nF. In general, the Y capacitor should be connected to the wire with greater noise interference;

Y capacitors are divided into Y1 capacitors and Y2 capacitors. Y1 is a double-insulated Y capacitor, which is used to bridge the primary and secondary sides; Y2 is a basic single-insulated Y capacitor, which is used to bridge the primary side to protect the earth, that is, the FG line.

Safety capacitors are used in such occasions that after the capacitor fails, it will not cause electric shock and will not endanger personal safety.

X safety capacitor safety level Allowable peak pulse voltage in application Overvoltage level (IEC664) X1 >2.5kV ≤4.0kV SW { {

X2 ≤2.5kV IY-F 6bXV

X3 ≤1.2kV }_.T.S@;9e

Y Safety Capacitor Safety Class Insulation Type Rated Voltage Range

Y1 Double insulation or reinforced insulation ≥ 250V

Y2 Basic insulation or supplementary insulation ≥150V ≤250V

Y3 Basic insulation or supplementary insulation ≥150V ≤250V

Y4 Basic insulation or supplementary insulation <150V

X capacitor suppresses differential mode interference

Y capacitor suppresses common mode interference

According to IEC 60384-14, capacitors are divided into X capacitors and Y capacitors,

1. X capacitance refers to the capacitor across L-N.

2. Y capacitor refers to the capacitor across L-G/N-G. (L=Line, N=Neutral, G=Ground) .

(1.) The most important purpose of adding Y-CAP is to pass EMI

(2.) Now most people do not want to add Y-CAP, there are two points:

a. In order to reduce costs, a Y-CAP has 0.3RMB, and now everyone is carrying out NO Y design

b. Our switching power supply has a lot of troubles when used on some audio equipment. For example, switching power supply for mp3 is not as good as linear power supply, fixed telephone, and switching power supply for ADSL will make noise;

3. The safety regulations do not say that Y-CAP must be added, as long as your EMI can pass, the Y-CAP will be too large and will affect the leakage current