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X and Y capacitors are safety capacitors, the X capacitor is between the live line and the neutral line, and the Y capacitor is between the live line and the ground. They are used in the power supply filter to filter the power supply and interfere with common mode and differential mode respectively. It plays a filtering role. Safety capacitors are used in such occasions, that is, after the capacitor fails, it will not cause electric shock and will not endanger personal safety. The peak pulse voltage overvoltage level allowed in the safety level of safety capacitors (IEC664) X1 > ;2.5kV ≤4.0kV Ⅲ X2 ≤2.5kV Ⅱ X3 ≤1.2kV ——Safety capacitor safety grade insulation type rated voltage range Y1 double insulation or reinforced insulation ≥ 250V Y2 basic insulation or supplementary insulation ≥150V ≤250V Y3 basic insulation or Additional insulation ≥150V ≤250V Y4 basic insulation or additional insulation <150V Y capacitor capacity must be limited, so as to control the magnitude of the leakage current flowing through it under the action of the rated frequency and rated voltage and the impact on the EMC performance of the system the goal of. GJB151 stipulates that the capacity of Y capacitor should not be greater than 0.1uF. In addition to complying with the corresponding grid voltage withstand voltage, Y capacitors are also required to have sufficient safety margins in terms of electrical and mechanical properties to avoid breakdown and short-circuit under extremely harsh environmental conditions. The withstand voltage performance of Y capacitors Protecting personal safety is of great significance.

　The safety capacitor has an X capacitor on the filter circuit, which is connected to the L-N line; the Y capacitor is the N-G line. In the safety standard, there are X1, X2, X3 capacitors according to the pulse voltage; Y1, Y2, Y3 according to the insulation level. (These are not classified according to what material, so I will learn more later.) As for the safety standards, there are some differences between countries, but the rated voltage is nothing more than 250 and 400. The safety capacitors made by major manufacturers are to meet the requirements of this safety standard. A safety capacitor can meet the requirements of Y capacitors, or it can be made to meet the requirements of X capacitors. Therefore, some safety capacitors are marked with X1Y1, X1Y2... 　　 A capacitor connected between the live wire and the 0 wire is X, and a capacitor connected between the live wire and the ground wire is like a Y. Due to the direct capacitance between the live wire and the 0 wire, it is affected by the voltage peak to avoid short circuits. The more important parameter is the withstand voltage level, and there is no fixed limit on the capacitance value. The direct capacitance between the live wire and the ground wire is related to the problem of leakage safety, so the parameter it pays attention to is the insulation level. As James Bai said, too large capacitance will have an impact on the device after the power is cut off. , Y2, Y3 points. (These are not classified according to what material, so I will learn more later.) As for the safety standards, there are some differences between countries, but the rated voltage is nothing more than 250 and 400. The safety capacitors made by major manufacturers are to meet the requirements of this safety standard. A safety capacitor can meet the requirements of Y capacitors, or it can be made to meet the requirements of X capacitors. Therefore, some safety capacitors are marked with X1Y1, X1Y2... 　　 A capacitor connected between the live wire and the 0 wire is X, and a capacitor connected between the live wire and the ground wire is like a Y. Due to the direct capacitance between the live wire and the 0 wire, it is affected by the voltage peak to avoid short circuits. The more important parameter is the withstand voltage level, and there is no fixed limit on the capacitance value. The direct capacitance between the live wire and the ground wire is related to the problem of leakage safety, so the parameter it pays attention to is the insulation level. As James Bai said, too large capacitance will have an impact on the device after the power is cut off.