What is the working principle of EMI filter

Because harmful EMI frequencies are much higher than normal signal frequencies, EMI filters work 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 at the same time it is a high frequency cutoff device, the rest of the EMI filter uses capacitors to shunt or shunt the harmful high frequencies noise so that these harmful high-frequency noises cannot reach sensitive circuits. In this way, EMI filters significantly reduce or attenuate all unwanted noise signals entering or leaving the protected electronics.
 
The electromagnetic interference filter is usually placed at the front end of the switching power supply connected to the grid, which is a low-pass filter composed of a series reactor and a parallel capacitor. As shown in Figure 1, the equivalent impedance of the noise source is Zsource, and the equivalent impedance of the grid is Zsink. Satons filter indicators (fstop and Hstop) can be implemented by first-order, second-order or third-order low-pass filters, and the calculation of the filter transfer function is usually approximated at high frequencies, that is, for n-order filters, all ωk is ignored Related items (when k output impedance does not match the interference brought to the filter characteristics.

DOREXS EMI FILTER

DOREXS power supply EMI filter is a passive low-pass filter, which transmits AC power to the power supply without attenuation, and greatly attenuates the EMI noise introduced with the AC power, and at the same time can effectively suppress the EMI noise generated by the power supply equipment, preventing They enter the AC grid and interfere with other electronic equipment.

In fact, the EMI filter is a four-terminal passive network composed of concentrated parameter components. The main components used are common-mode inductor coils L1, L2, differential-mode inductors L3, L4, and common-mode capacitors CY1, CY2 and differential-mode capacitors. CX.
If this filter network is placed at the input end of the power supply, then L1 and CY1 and L2 and CY2 respectively constitute low-pass filters between two pairs of independent ports on the AC incoming line, which can attenuate the common-mode interference existing on the AC incoming line noise, preventing them from entering the power supply.

The common-mode inductance coil is used to attenuate the common-mode noise on the AC incoming line. L1 and L2 are generally wound in the same direction on the ferrite core of the closed magnetic circuit with the same number of turns. The magnetic flux generated by the alternating current in the two coils cancels each other out, so that the magnetic core does not cause magnetic flux saturation, and the inductance value of the two coils is larger in the common mode state and remains unchanged.
The differential-mode inductance coils L3, L4 and the differential-mode capacitor CX form a low-pass filter between the independent ports of the AC incoming line, which is used to suppress the differential-mode interference noise on the AC incoming line and prevent the power equipment from being disturbed by it.

Next, DOREXS will take you to see how the power supply EMI filter achieves effective filtering?

Since 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 at the same time it is a high frequency cutoff device, the rest of the EMI filter uses capacitors to shunt or shunt the harmful high frequencies noise so that these harmful high-frequency noises cannot reach sensitive circuits. In this way, EMI filters significantly reduce or attenuate all unwanted noise signals entering or leaving the protected electronics.

The electromagnetic interference filter is usually placed at the front end where the switching power supply is connected to the power grid. The equivalent impedance of the noise source is Zsource, and the equivalent impedance of the grid is Zsink. The Satons filter indicators (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 to say, for n-order filters, all ωk related term (when k output impedance is not matched) interferes with the filter characteristics.\

DOREXS EMI industry leader

If you need effective EMI protection, DOREXS offers durable and reliable EMI filters for every application. Our filters are suitable for professional applications in the military and medical fields, as well as for residential and industrial use. For applications requiring a custom solution, our professional team can design an EMI filter to meet your specific requirements.

With 15 years of experience in solving electromagnetic interference, DOREXS is a trusted manufacturer of high-quality EMI filters for medical, military, and commercial applications. All of our EMI filters are designed to meet industry standards and comply with EMC regulations. Explore our selection of EMI filters or submit a custom quote request to get the perfect EMI filter for your needs. For more information on DOREXS custom and standard EMI filters, please contact us.

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