What is the function of using noise filters in power equipment
The power supply of electronic devices, such as 220V/50Hz AC power grids or 115V/400Hz AC generators, contains various types of EMI noise. Among them, artificial EMI interference sources, such as radio transmission signals from various radar, navigation, communication and other equipment, will induce electromagnetic interference signals on the power lines and connecting cables of electronic devices. Electric rotating machinery and ignition systems will generate transient processes and radiated noise interference in inductive load circuits; There are also natural sources of interference, such as lightning discharge phenomena and electromagnetic interference noise in the universe. The former has a short duration but high energy, while the latter has a wide frequency range. In addition, electronic circuit components themselves also generate thermal noise during operation.
These electromagnetic interference noises, coupled through radiation and conduction, can affect the normal operation of various electronic devices operating in this environment.
On the other hand, electronic devices also generate various types of electromagnetic interference noise during operation. For example, digital circuits use pulse signals (square waves) to represent logical relationships, and Fourier analysis of their pulse waveforms reveals a wide range of harmonic spectra. In addition, there are multiple repeated frequency pulse trains in digital circuits, which contain richer harmonics, wider spectra, and more complex electromagnetic interference noise.
Various types of regulated power supplies themselves are also sources of electromagnetic interference. In a linear regulated power supply, the unidirectional pulsating current formed by rectification can also cause electromagnetic interference; Switching power supplies have the advantages of small size and high efficiency, and are increasingly used in modern electronic devices. However, because they are in a switching state during power conversion, they are a strong source of EMI noise. The EMI noise generated by them has a wide frequency range and high intensity. These electromagnetic interference noises also pollute the electromagnetic environment through radiation and conduction, thereby affecting the normal operation of other electronic devices.
For electronic devices, when EMI noise affects analog circuits, it can deteriorate the signal-to-noise ratio of signal transmission, and in severe cases, the signal to be transmitted can be overwhelmed by EMI noise and unable to be processed. When EMI noise affects digital circuits, it can cause logical relationship errors, leading to incorrect results.
For power equipment, in addition to the power conversion circuit, there are also drive circuits, control circuits, protection circuits, input/output level detection circuits, and other complex circuits inside. These circuits are mainly composed of general or specialized integrated circuits. When they malfunction due to electromagnetic interference, the power supply will stop working, causing electronic devices to malfunction. The use of power grid noise filters can effectively prevent the power supply from malfunctioning due to external electromagnetic noise interference.
