Some Measures to Suppress Interference of Switching Power Supply
The three elements that form electromagnetic interference are the source of disturbance, the route of transmission, and the disturbed equipment. Therefore, the suppression of electromagnetic interference should also take appropriate measures from these three aspects. First of all, the source of disturbance should be suppressed and the cause of the interference should be directly eliminated; secondly, the coupling and radiation between the source of disturbance and the disturbed device should be eliminated, and the propagation path of electromagnetic interference should be cut off; sensitivity. At present, several measures to suppress interference are basically used to cut off the coupling channel between the electromagnetic disturbance source and the disturbed equipment. Common methods are shielding, grounding and filtering.
1) The electromagnetic radiation interference of the switching power supply can be effectively suppressed by using shielding technology, that is, the electric field is shielded with materials with good conductivity, and the magnetic field is shielded with materials with high magnetic permeability. Shielding has two purposes, one is to limit the leakage of electromagnetic energy radiated inside, and the other is to prevent external radiation interference from entering the internal area. The principle is to use the shielding body to reflect, absorb and guide electromagnetic energy. In order to suppress the radiation generated by the switching power supply and the influence of electromagnetic disturbance on other electronic equipment, the shielding cover can be processed completely according to the method of shielding the magnetic field, and then the entire shielding cover is connected with the system casing and the ground as a whole, and the electromagnetic field can be protected. effective shielding.
2) The so-called grounding is to establish a conductive path between two points in order to connect electronic equipment or components to certain reference points called "ground". Grounding is an important method for switching power supply equipment to suppress electromagnetic interference. Some parts of the power supply are connected to the ground to suppress interference. The principle of "one-point grounding" should be followed in circuit system design. If multi-point grounding is formed, a closed grounding loop will appear, and magnetic induction noise will be generated when the magnetic force lines pass through the loop. In fact, it is difficult to achieve "one-point grounding". Therefore, in order to reduce grounding impedance and eliminate the influence of distributed capacitance, planar or multi-point grounding is adopted. A conductive plane is used as a reference ground, and all parts that need to be grounded are connected to the reference ground nearby. . To further reduce the voltage drop in the ground loop, bypass capacitors can be used to reduce the magnitude of the return current. In a circuit system where low frequency and high frequency coexist, the ground wires of the low frequency circuit, high frequency circuit, and power circuit should be connected separately and then connected to the common reference point.
3) Filtering is an effective method to suppress conducted interference, and plays an extremely important role in the electromagnetic compatibility design of equipment or systems. As an important unit to suppress the conduction interference of the power line, the EMI filter can suppress the interference from the power grid to the power supply itself, and can also suppress the interference generated by the switching power supply and fed back to the power grid. In the filter circuit, many special filter components are also used, such as feedthrough capacitors, three-terminal capacitors, and ferrite magnetic rings, which can improve the filter characteristics of the circuit. Appropriate design or selection of filters, and correct installation and use of filters are important components of anti-jamming technology.
