The interference signal of the switching power supply module is always one of the key processing points. From the basic principle, the key of the interference signal comes from two levels, namely transmission dry torsion and radiation source dry torsion.

The transmission of dry torsion is due to the existence of parasitic parameters in the power circuit and the opening and resolution of the switching power module in the power transformer, which causes great common mode interference and differential mode dry torsion in the communication and AC input end of the power transformer.

The radiation source drywall refers to the size and function of the electromagnetic induction caused by the change of the electric flux in the electric conductor, which in turn causes the change of the electrostatic field in the surrounding indoor space.

To ease and contain the disturbance signal of power network and electronic products, set the X and Y capacitor, capacitor at least X capacitor filter effect, common in differential mode filter, and inductance matching, series on either side of type, filter out the L, N line in the middle of the module according to the signal, can prevent opening to the outside world dry scratching.

The main grounding device of The Y capacitor, common in common mode filters, is applied symmetrically, connecting L to the ground or N to the ground, and filtering out the difference modulus data signal between L to the ground or N to the ground. Applying the limit of scene leakage current, the Y capacitor value should not be very large.

Usually for a protective switching power supply, Y capacitors are added to the middle and secondary to show the secondary common-mode current to the middle and reduce the damage of common-mode current to the output.

The high voltage and bottom voltage detection of many power transformers adopt safety capacitance with the purpose of filtering out high harmonics, avoiding dry torsion and improving the output working voltage quality.