A brief talk on the role of Y capacitance in electromagnetic interference

Y capacitor is an safety capacitor, after the failure of the capacitor will not lead to electric shock, the person will not be harmed, Y capacitor is the transfer of the power line between the two lines and the ground (L-E,N-E) capacitance, generally in pairs, can be used to suppress common-mode interference.

Y capacitance in electromagnetic interference can also play a big role, the following and we talk about it. When the switching power supply works, the parasitic capacitance of the power transformer transmits the common-mode interference to the rear circuit, and after the rear circuit, the common-mode interference will be transmitted to the Earth through the parasitic capacitance with the Earth, and then from the Earth to the conduction test instrument, back to the primary.

If there is no Y capacitor, most of the common-mode interference will return to the primary through the Earth flow through the conduction test instrument, resulting in the conduction test instrument detected by the conduction interference exceeding the standard. Therefore, the general power supply design will be in the primary rectifier and secondary between the addition of Y capacitor, Y capacitor will be the original flow through the Earth common-mode interference bypass to the primary rectifier, thus 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 is tested by the relevant conduction interference.

Y capacitors provide a common-mode noise path between primary and secondary in the power supply, allowing most common-mode noise to flow inside the power supply, reducing external conduction and radiation interference through the power supply input line and the output line. In addition, to improve the EMI in the circuit can choose to reduce the amount of interference source and cut or change the propagation path of interference, in the absence of Y capacitance, but also through the special power module through the adjustment of the circuit principle, reduce the parasitic parameters of the power supply and other aspects, for the instrument back-end sampling to provide a clean and reliable power supply.

At the same time with a simple outer ring circuit, successfully passed the instrument equipment of various industry standards testing. If you have technical questions can contact us, we strive to solve for you.