The role of Y capacitor in electromagnetic interference

Y capacitors are safety capacitors. After the capacitor fails, it will not cause electric shock and the human body will not be harmed. The Y capacitor is a capacitor that is connected between the two lines of the power line and the ground (L-E, N-E), and is generally present in pairs and can be used to suppress common mode interference. Y capacitors can also play a large role in electromagnetic interference.

When the switching power supply is working, the parasitic capacitance of the power transformer transmits the common mode interference to the rear stage circuit. After the latter stage circuit, the common mode interference is transmitted to the earth through the parasitic capacitance of the earth, and then transmitted from the earth to the conduction test instrument. Back to the beginning. If there is no Y capacitor, most of the common mode interference will flow back to the primary through the conduction test instrument, causing the conducted interference detected by the conduction test instrument to exceed the standard.

Therefore, the general power supply design will add a Y capacitor between the primary rectification ground and the secondary ground. The Y capacitor bypasses the common mode interference flowing through the ground to the primary rectification ground, thereby greatly reducing the common mode interference flowing through the earth. By increasing the external capacitance, the interference noise detected by the conduction test instrument is greatly reduced, so that the power supply passes the relevant conducted interference test. The Y capacitor provides a common mode noise path between the primary and secondary in the power supply, allowing most of the common mode noise to flow inside the power supply, reducing interference and conduction through the power input and output lines.

In addition, improving the EMI in the circuit can choose to reduce the amount of the interference source and cut off or change the propagation path of the interference amount. In the absence of the Y capacitor, the power supply parasitic parameters can be reduced by adjusting the circuit principle through a special power supply module. In terms of aspects, it provides a clean and reliable power supply for sampling the back end of the instrument. At the same time, with the simple outer ring circuit, it successfully passed the various industry standard tests of instrumental equipment.

If you have technical problems, please contact us and you will try your best to solve it.