The most comprehensive analysis of X/Y safety capacitors in power supply filtering (III)

Safety capacitors are used in applications where the capacitor does not cause an electric shock and does not endanger personal safety. It includes X and Y capacitors.

The X capacitor is a capacitor that is connected between the two lines of the power line (LN). Generally, a metal film capacitor is used. The Y capacitor is a capacitor that is connected between the two lines of the power line and the ground (LE, NE), and is generally in pairs. . Based on the limitation of leakage current, the value of Y capacitor should not be too large. Generally, the X capacitor is uF grade, and the Y capacitor is nF grade. The X capacitor suppresses differential mode interference and the Y capacitor suppresses common mode interference.

Safety Capacitor Safety Level:

Safety Capacitance Safety Level, Peak Pulse Voltage Overvoltage Level Allowed in Applications (IEC664)

X1 >2.5kV ≤4.0kV III

X2 ≤2.5kV II

X3 ≤1.2kV ——

Safety capacitor safety class, insulation type, rated voltage range

Y1 double insulation or reinforced insulation ≥ 250V

Y2 basic insulation or additional insulation ≥150V ≤250V

Y3 basic insulation or additional insulation ≥150V ≤250V

Y4 basic insulation or additional insulation <150V

The capacitance of the Y capacitor must be limited to achieve the purpose of controlling the leakage current flowing through it under the rated frequency and rated voltage and the impact on the EMC performance of the system. GJB151 specifies that the capacity of the Y capacitor should be no more than 0.1uF. In addition to the corresponding grid voltage withstand voltage, the Y capacitor also requires sufficient safety margin for electrical and mechanical performance to avoid breakdown and short circuit under extreme environmental conditions. The pressure resistance of the Y capacitor is correct. Protecting personal safety is of great significance.

Add a little more to choose where to pay attention:

Capacitors for suppressing power supply electromagnetic interference:

When capacitors are used in a power-over line circuit to eliminate noise, not only the normal voltage, but also the generation of abnormal pulse voltages (such as lightning) must be considered, which may cause the capacitor to smoke or catch fire. Therefore, the safety standards for over-the-line capacitors are strictly regulated in different countries, so it is necessary to use safety-certified capacitors.