1 Preface
Electromagnetic interference in switching power supply modules has always been an important solution point. In principle, electromagnetic interference mainly comes from two aspects, which are conducted interference and radiation interference.
2 Conducted interference
Due to the existence of parasitic parameters in the circuit, as well as the switching power supply in the FM switching device on and off, so that the switching power supply in the mains AC input to produce a large common mode interference and differential mode interference.
3 Radiation interference
As the change of current in the conductor will produce a changing magnetic field in the space around it, and the changing magnetic field produces a changing electric field, the amplitude and frequency of this changing current determines the size of the electromagnetic generated and its range of action. In order to mitigate and resist the harm caused by these electromagnetic disturbances to the power grid and electronic equipment, engineers add X and Y capacitors to the circuit design.
4 X Capacitor Role
The X capacitor is used to eliminate differential mode interference. It is mainly used for filtering, matching with the common mode inductor, and connected in parallel at both ends of the input to filter out the differential mode signal between L and N lines. Usually, it is used to use mylar film type capacitor with high ripple current resistance, which is larger in size and allows larger instantaneous charging and discharging current, while its internal resistance is smaller accordingly. In addition, the X capacitor will also use the plastic square high-voltage CBB capacitor, CBB capacitor not only has better electrical performance, but also can effectively reduce the impact of high frequency pulse on the power supply when connected in parallel with the input of the power supply.
2kv-1000uf магнитизатор конденсатор-импульс конденсатор-высокое напряжение магнитизатор конденсатор

2kv-1000uf магнитизатор конденсатор-импульс конденсатор-высокое напряжение магнитизатор конденсатор

5 X capacitor application
Generally two pins are connected across the zero and fire wires, suitable for high frequency, DC, AC, coupling, across the pulse circuit, can withstand overvoltage shock, generally used in parallel with the resistor, the purpose is to play the role of charge discharge.
6 Y capacitor role
Y capacitor is used to eliminate common mode interference. The capacitors are connected between the two lines of power line and ground (L-E, N-E), generally in pairs, to filter out high harmonics, prevent interference and improve the quality of output voltage. Based on the limitation of leakage current, the value of Y capacitor cannot be too large, and Y capacitor usually adopts the high-voltage porcelain chip.
7 Y capacitor application
Many isolated switching power supplies add Y capacitors on the primary and secondary in order to provide a circuit for the common mode current of the secondary to the primary and reduce the impact of common mode current on the output. Choose high-voltage ceramic capacitor as Y capacitor, Y capacitor is usually connected in four ways: ① input, and common mode inductor to form a filter, L and N are added to PE ② energy storage capacitor positive and negative to PE plus (as shown in Figure 4) ③ output to PE plus ④ transformer primary and secondary cross-connected
X capacitor and Y capacitor belong to the same safety capacitor. When the safety-regulated capacitor fails, it will not produce electric shock and will not endanger personal safety. The safety-regulated capacitor is usually used in the anti-interference circuit to play the role of filtering. The discharge of the safety-regulated capacitor is different from the ordinary capacitor, which retains the charge for a long time after the external power is disconnected. The X and Y capacitors are used in switching power supply for different purposes, and they are not interchangeable.
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