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With the popularization and development of the digital circuits of switching power supply, the electromagnetic waves radiated and leaked by electronic devices not only seriously interfere with the normal operation of other electronic devices, leading to equipment malfunction, transmission errors and control failures, but also threat to human health and safety. Become an invisible pollution, not inferior to the water, air, noise and other tangible pollution hazards. Therefore, reducing the electromagnetic interference (EMI) of electronic equipment has become the world's electronics industry concerns.

Anti - interference line filters characteristics

There is a conceptual difference between an anti-jamming filter and a conventional signal filter. Signal filter in the impedance matching conditions, that is, through the filter to maintain the input and output signal amplitude does not change the premise that part of the frequency domain for the expected processing and transformation. While the EMI filter is used to suppress the electromagnetic interference from entering the equipment and from the equipment, with bidirectional suppression. So this requires the EMI filter at the port and the device to produce the greatest mismatch. So as to make the filter attenuation of electromagnetic interference equal to the attenuation of their own network coupled with the input and output ports of reflection, must follow the following rules. Where Rs is the input impedance of the grid and varies with the amount of charge; RL is the output impedance of the EMI filter, which varies with the load size.

Selection of common mode choke coil Material in EMI Filter

Reduce the electronic equipment of electromagnetic interference has become a key issue whether the electronic products market. The soft magnetic materials have become EMI filter essential components, and plays a pivotal role. Now with the soft magnetic materials made of various suppression EMI components are widely used in various electronic circuits and equipment. This is because the soft magnetic material has its unique performance, resulting in the field of anti-electromagnetic interference play a major role. However, it is unrealistic for electronics manufacturers to expect universal EMI filters to reduce interference to below standard for all electronic devices. EMI filter design should be based on the EMC standards for electronic equipment, that is, need to attenuate the EMI signal frequency range and the level of excessive levels to select, in particular, the soft magnetic materials.

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