Plication and basic principle of modular power supply noise filter

There are all kinds of EMI noise in 220v/50hz AC power grid or 115v/400hz alternator. Among them, artificial EMI interference sources, such as radio emission signals of various radar, navigation, communication and other equipment, will sense electromagnetic interference signals on the power line and the connecting cables of electronic equipment. Electric rotating machinery and ignition system will produce transient process and radiated noise interference in the inductive load circuit, as well as natural interference sources, such as lightning discharge signs and space electrical interference noise in the universe. The former has short duration but large energy, and the latter has a wide frequency range. In addition, when electronic circuit components work, they will also produce thermal noise. These electromagnetic interference noises, through the way of radiation and conduction coupling, will affect the normal work of various electronic equipment operating in this environment.

On the other hand, electronic equipment will also produce a variety of electromagnetic interference noise when working. For example, digital circuits use pulse signals (square waves) to reveal the expression of logical relations. The analysis of its pulse waveform shows that its harmonic spectrum range is very wide. In addition, there are many kinds of pulse trains with repetition frequency in the digital circuit. These pulse trains contain stronger harmonics, wider spectrum and more complex electromagnetic interference noise. Various voltage stabilizing module power supplies are also a source of electromagnetic interference. In the linear voltage stabilizing module power supply, the unidirectional pulsating current formed by rectification will also cause electromagnetic interference. Switching module power supply has the advantages of small size and high compliance, which is more and more widely used in contemporary electronic equipment. However, because it is in the switching state during power conversion, it is a strong EMI noise source, and the EMI noise generated by it has a wide frequency range and high intensity. These electromagnetic interference noises also pollute the electromagnetic environment through radiation and conduction, thus affecting the normal work of other electronic equipment.

For electronic equipment, when EMI noise affects the analog circuit, the signal-to-noise ratio of signal transmission will deteriorate, and when nervous, the signal to be transmitted will be swallowed by EMI noise and cannot be processed. When EMI noise affects the digital circuit, it will cause the logic relationship error, resulting in the wrong effect. For the module power supply equipment, in addition to the power conversion circuit, there are also drive circuit, control circuit, treasure circuit, input and output level detection circuit, etc. the circuit is quite complex. These circuits are mainly composed of general-purpose or special-purpose integrated circuits. When misoperation occurs due to electromagnetic interference, the module power supply will stop working, resulting in the failure of electronic equipment to work normally.