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Can EMC rectify? Let's take a look at EMC's specific rectification methods!

Published on.

2022-06-10 09:24

EMC (electromagnetic compatibility) refers to the ability of equipment or system to operate as required in its electromagnetic environment without causing intolerable electromagnetic interference to any equipment in its environment. Therefore, EMC rectification includes two requirements: on the one hand, the electromagnetic interference generated by the equipment to the environment during normal operation cannot exceed a certain limit; On the other hand, it means that electrical appliances have a certain degree of immunity to electromagnetic interference of the environment, namely electromagnetic sensitivity.

First, we should diagnose the product according to the actual situation, analyze its interference sources and mutual interference methods. According to the analysis results, EMC rectification is targeted. In general, the main EMC rectification methods are as follows:
1. Reduce interference sources. On the basis of finding the interference source, the interference source can be weakened within the allowable range. The general methods to weaken the source are: add a decoupling capacitor between Vcc and GND of IC, the capacity of this capacitor is between 0.01F and 0.1F, and pay attention to the capacitor lead during installation, and try to keep it as short as possible; The attenuator is added while ensuring the sensitivity and signal-to-noise ratio. For example, the crystal oscillator in VCD and DVD players has a serious impact on electromagnetic compatibility. Reducing its amplitude is one of the feasible methods, but it is not the only solution. Another indirect method is to keep the signal line away from the interference source.
2. Improve the grounding system. The ideal ground wire is a physical entity with zero impedance and zero potential. It is not only the reference point of the signal, but also does not produce voltage drop when the current flows. In specific electrical and electronic equipment, this ideal grounding wire does not exist. When current flows through the grounding wire, voltage drop will inevitably occur. According to the formation mechanism of ground wire interference, it can be summarized as follows: First, reduce the low impedance and the impedance of the power supply feeder. Secondly, correctly select the grounding mode and lockout grounding circuit. According to the grounding mode, there are floating grounding, single point grounding, multi-point grounding and mixed grounding.
3. Shielding. Shielding is one of the important measures to improve the electromagnetic compatibility of electronic systems and equipment. It can effectively restrain various electromagnetic interference propagating through space. According to the shielding mechanism, it can be divided into magnetic field shielding, electric field shielding and electromagnetic shielding. Pay attention to the following points for electric field shielding: select materials with high conductivity and good grounding; The shielding layer can be directly grounded by selecting the correct grounding point and reasonable shape. Magnetic shielding usually refers to the shielding of DC or very low frequency magnetic field, and its shielding effectiveness is far less than that of electric field shielding and electromagnetic shielding.
4. Change the wiring structure of the circuit board. Some frequency points are determined by the distribution parameters of the wiring on the circuit board, but the methods mentioned above are not very useful. This rectifier changes the circuit parameter structure by adding small inductors, capacitors and magnetic beads in the wiring to move it to a higher frequency point. For this interference, if you want to fundamentally solve its impact, you need to re route.
The first several EMC rectification methods are conducive to improving electromagnetic compatibility, but they are widely used to change the ground wire structure and arrange wires and cables. These EMC rectification methods not only save costs, but also are very effective rectification methods. In the actual rectification, the method of changing the ground wire structure, sorting out and shielding wires and cables shall be the main method, supplemented by other methods.