The interference signal of power off module is always a key processing point. From the basic principle, the key interference signal comes from two levels, namely transmission interference and radiation interference.
Transmission interference is due to the existence of parasitic parameters in the power supply circuit and the enabling and resolving of switching power supply module in the power transformer, which makes the power transformer cause great common mode interference and differential mode interference at the communication input end.
The radiation source interference refers to the electromagnetic field in the surrounding indoor space caused by the change of electric flow in the electric conductor, and the transformed electromagnetic field causes the transformed electrostatic field. The magnitude and frequency of the transformed electric flow determine the size and function category of the electromagnetic induction.
In order to alleviate and contain the damage caused by this interference signal to the power grid and electronic products, X capacitor and Y capacitor are set up. At least, the main filter function of X capacitor is common in differential mode filter, which is paired with common mode inductor and connected in series on both sides of the input. The differential mode data signal in the middle of L and N lines is filtered out, so as to prevent external interference.
The main grounding device of Y capacitor is commonly used in common mode filter, symmetry application, connected between L and ground or n to ground, filtering out the differential mode data signal between L and ground or n to ground. For the limitation of leakage current in application scenarios, the value of Y capacitor can not be very large.
It is usually a protective switching power supply. Adding Y capacitors to the primary, intermediate and secondary is to show a control circuit to the secondary common mode current, so as to reduce the harm of the common mode current to the output.
Many high voltage detection and bottom voltage detection of power transformer are based on safety capacitor, so as to filter out high-order harmonics, avoid interference and improve the quality of output voltage.
