Both the X safety capacitor and Y safety capacitor are safety capacitors. The difference is that the X capacitor is connected across the input line to eliminate the differential mode. The Y capacitor is connected between the input line and the ground line to eliminate common mode.The X safety capacitor uses a plastic square-shaped high-voltage CBB capacitor. The CBB capacitor not only has better electrical performance, but also in parallel with the input of the power supply can effectively reduce the impact of high-frequency pulse on the switching power supply.

Y safety capacitors have high voltage ceramics. The Y safety capacitor is connected between the phase and ground. In order not to exceed the ground allowable leakage value defined by the relevant safety standards, the value of these capacitors is approximately a few nF. In general, the Y safety capacitor should be connected to the noisy wire;

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

x-safety-capacitor-and-Y-safety-capacitorSafety capacitance refers to the situation where the capacitor fails and does not endanger personal safety.

X Safety Capacitance Safety Level Peak Pulse Voltage Allowed in Application Overvoltage Rating (IEC664) X1 >2.5kV ≤4.0kV,X2 ≤ 2.5kV,X3 ≤ 1.2kV

Y Safety Capacitor Safety Rating 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
  • X capacitance suppression differential mode
  • Y capacitance suppresses common mode

Accoding to IEC 60384-14, capacitors are divided into X capacitors and Y capacitors.
1. The X capacitance refers to the capacitor that spans between L-N.
2. Y-capacitance refers to the capacitor that spans between L-G/N-G. (L=Line, N=Neutral, G=Ground).
(1.) The most important purpose of adding Y-CAP is to pass EMI.
(2.) 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. Now everyone is designing NO Y.
b. Our switching power supply has many problems when used on some audio devices, such as mp3 switching power supply does not use a linear power supply, fixed telephone, ADSL switching power supply will have noise;
3. The safety regulations do not say that Y-CAP must be added, as long as your EMI can be over, Y-CAP too much will affect the leakage current.