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FAQs

What are the classification and criteria for filters?

(1) low pass filter

From 0 to F2, the amplitude-frequency characteristics are flat, which can make the frequency components below F2 pass through almost unattenuated, while those higher than F2 are greatly attenuated.

(2) high-pass filter

In contrast to low-pass filtering, its amplitude-frequency characteristics are flat from frequency F1 to infinity. It allows the frequency components of the signal above F1 to pass through almost unattenuated, while those below F1 will be greatly attenuated.

(3) band pass filter

Its passband is between F1 and F2. It allows the frequency components of the signal higher than F1 and lower than F2 to pass through unattenuated, while other components are attenuated.

(4) band stop filter

In contrast to bandpass filtering, the stop band is between frequencies F1 and F2. It attenuates the frequency components of the signal higher than F1 and lower than F2, and the rest of the frequency components pass through almost unattenuated.

What is the EMI power filter?

Electromagnetic interference (EMI) power filter is a passive device composed of inductance and capacitance. It actually acts as two low-pass filters, one attenuating common-mode interference and the other attenuating different-mode interference. It attenuates rf energy in the stop band (usually greater than 10KHz) and allows the power frequency to pass through with little or no attenuation. EMI power filters are the first choice for electronic design engineers to control conducted and radiated EMI.

What is the working principle of EMI power filter?

(A) By using the characteristics of capacitor passing high frequency and low frequency isolation, the high frequency interference current of live wire and neutral wire is introduced into the ground wire (common mode), or the high frequency interference current of live wire is introduced into the neutral wire (differential mode);

(B) Reflect high-frequency interference current back to the interference source by using the impedance characteristics of the inductor coil;

What should be paid attention to in the installation of filter?

To reduce the grounding resistance, the filter should be installed on the conductive metal surface or connected to the ground point nearby through the braided ground zone to avoid large grounding impedance caused by slender grounding wires

How to select power filter?

Several indexes should be considered when selecting power line filter. The first is rated voltage/rated current, followed by insertion loss, leakage current (dc power filter does not consider the size of leakage current), structure size, and finally is the voltage test. Since the interior of the filter is generally potting, the environmental characteristics are not a major concern. However, the temperature characteristics of the potting material and the filter capacitor have a certain influence on the environmental characteristics of the power supply filter.

The volume of the filter is mainly determined by the inductance in the filter circuit. The larger the volume of the inductance coil, the larger the volume of the filter.