# How to do electromagnetic interference

- Sep 28, 2019-

How to do electromagnetic interference

How to do electromagnetic interference? To make an oscillator, the two ends of the inductor in the oscillator are grounded at one end, and the other end is made into an antenna. The interference signal is transmitted. If the oscillation frequency of the oscillator is adjustable, the frequency of the interference signal transmitted is It will change.

How electromagnetic interference works

Because the frequency of harmful electromagnetic interference is much higher than the normal signal frequency, the electromagnetic interference filter works by selectively blocking or shunting harmful high frequencies.

Basically, the inductive part of the EMI filter is designed as a low-pass device to pass the AC line frequency, and it is also a high-frequency cut-off device. Other parts of the EMI filter use capacitors to shunt or shunt harmful high frequencies. Noise makes these harmful high-frequency noises unable to reach sensitive circuits. Thus, the EMI filter significantly reduces or attenuates all unwanted noise signals entering or leaving the protected electronic device.

The EMI filter is usually placed at the front end of the switching power supply connected to the grid. It is a low-pass filter consisting of a series reactor and a shunt capacitor. As shown on the right, the noise source equivalent impedance is Zsource and the grid equivalent impedance is Zsink. The Satons filter indices (fstop and Hstop) can be implemented by first-order, second-order or third-order low-pass filters. The calculation of the filter transfer function is usually approximated at high frequencies, that is, for n-order filters, all ωk are ignored. Related items (when k "n), only the ωn related items are taken. Special attention should be paid to the interference caused by the input and output impedance mismatches to the filtering characteristics.