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This article shows you what the common small methods of EMC rectification are, the content is concise and easy to understand, it can definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

In this paper, the problems commonly used in EMC rectification and reform are discussed and discussed.

First of all, the products should be diagnosed according to the actual situation, and the sources of interference and the ways and ways of mutual interference should be analyzed. Then according to the results of the analysis, targeted rectification and reform.

Generally speaking, the main rectification methods are as follows:

1. Weaken the interference source. On the basis of finding the interference source, the interference source can be weakened within the allowable range. The methods of weakening the source are generally as follows:

1) A decoupling capacitor is added between Vcc and GND of IC, and the capacity of the capacitor is 0. 01 μ F jujube 0. Between 1 μ F, pay attention to the lead of the capacitor during installation so that it is as short as possible.

2) add an attenuator while ensuring sensitivity and signal-to-noise ratio. For example, the crystal oscillator in VCD and DVD video players has a serious impact on electromagnetic compatibility, so reducing its amplitude is one of the feasible methods, but it is not the only solution.

3) another indirect way is to keep the signal line away from the interference source.

2. the classification and arrangement of wires and cables, in electronic equipment, wire-to-wire coupling is not only an important way, but also an important cause of interference, because the factor of frequency can be divided into high-frequency coupling and low-frequency coupling. Due to the different coupling methods, the rectification methods are also different, which are discussed below:

1) low-frequency coupling and low-frequency coupling refers to the case that the length of the wire is equal to or less than 16 wavelengths, and the low-frequency coupling can be divided into electric field and magnetic field coupling. The physical model of electric field coupling is capacitive coupling. Therefore, the main purpose of rectification is to reduce the distributed coupling capacitance or the amount of coupling. The following methods can be adopted:

A. Increasing the distance between circuits is the most effective way to reduce the distributed capacitance.

B, add a high conductivity shield, and make the shield single point grounding can effectively restrain the interference of low frequency electric field.

C. The additional filter can reduce the coupling between the two circuits.

D, reduce the input impedance, for example, the input impedance of the CMOS circuit is very high, and it is extremely sensitive to electric field interference, so it can connect a capacitor or a resistance with low resistance at the input within the allowable range.

2) the physical model of magnetic field coupling is inductive coupling, and its coupling is mainly through the distributed mutual inductance between lines, so the main method of rectification is to destroy or reduce the amount of coupling, generally speaking, the following methods can be adopted:

A, additional filter, in the additional filter (electric 13169590065), we should pay attention to the input and output impedance of the filter and its frequency response.

B. reduce the loop area of the sensitive loop and the source loop, that is, make the signal line or current-carrying line close to or twist with its loop as far as possible.

C, increase the distance between the two circuits in order to reduce the mutual inductance between the lines to reduce the amount of coupling.

D. If possible, make the sensitive circuit orthogonal or nearly orthogonal to the plane of the source circuit to reduce the coupling between the two circuits.

E, bandaging sensitive lines with high magnetic conductivity materials can effectively solve the problem of magnetic field interference, it is worth noting that to form a closed and magnetic circuit, efforts to reduce the magnetoresistance of the magnetic circuit will be more effective.

3) High frequency coupling and high frequency coupling refers to the alignment longer than 1 beat 4 wavelengths, which will enhance the coupling due to the standing wave of voltage and current in the circuit, which can be solved by the following methods:

A, shorten the grounding wire as much as possible, and grounding with the shell adopts the way of surface contact as far as possible.

B, rearrange the input and output lines of the filter to prevent the coupling between the input and output lines and ensure that the filtering effect of the filter is not bad.

C. The shielding layer of shielded cable adopts multi-point grounding.

D. Connect the hanging pin of the connector to the ground potential to prevent its antenna effect.

3. To improve the ground wire system, the ideal ground wire is a physical entity with zero impedance and zero potential, which is not only the reference point of the signal, but also does not produce voltage drop when the current flows through. In the specific electrical and electronic equipment, this ideal ground wire does not exist, when the current flows through the ground wire, it is bound to produce voltage drop. According to the formation mechanism of interference in the ground wire, it can be summarized into the following two points:

1) reduce the low impedance and power feeder impedance.

2) correctly select the grounding mode and the barrier ground loop, which can be divided into suspended ground, single-point grounding, multi-point grounding and mixed grounding according to the grounding mode. If the interference of the sensitive line mainly comes from the external space or the shell of the system, it can be solved by suspended ground, but the suspended equipment is easy to produce electrostatic accumulation, and electrostatic discharge will occur when the charge reaches a certain level. therefore, the suspended ground is not suitable for general electronic equipment. Single-point grounding is suitable for low-frequency circuits. in order to prevent the ground potential difference between the points of power frequency current and other stray current on the signal ground wire, the signal ground wire is isolated from the power supply and safety ground wire. Single point grounding is mainly suitable for cases where the frequency is lower than 3MHz. Multi-point grounding is the only practical grounding method for high-frequency signals, which will show the characteristics of transmission lines at radio frequency. In order to make multi-point grounding effective, when the length of grounding conductor exceeds the maximum frequency of 1ppm 8 wavelength, multi-point grounding requires an equipotential grounding plane. Multi-point grounding is suitable for 300KHz or above. Hybrid grounding is suitable for electronic circuits with both high frequency and low frequency.

4. Shielding is one of the important measures to improve the electromagnetic compatibility of electronic systems and electronic equipment, which can effectively restrain all kinds of electromagnetic interference transmitted through space. According to the mechanism, shielding can be divided into magnetic shielding, electric field shielding and electromagnetic shielding. The shielding of electric field should pay attention to the following points:

1) choose materials with high electrical conductivity and good grounding.

2) choose the correct grounding location and reasonable shape, preferably with the shield directly grounded.

5. Magnetic field shielding usually refers to the shielding of DC or very low frequency magnetic fields, and its shielding effectiveness is far lower than that of electric field shielding and electromagnetic shielding. Magnetic shielding is often the focus of engineering.

1) ferromagnetic materials should be selected.

2) the magnetic shield should be far away from the magnetic components to prevent magnetic short circuit.

3) double-layer shield or even three-layer shield can be used.

4) the opening on the upper side of the shield should pay attention to the direction of the opening, make the long side of the seam parallel to the magnetic flux flow direction as far as possible, and minimize the increase of the magnetic circuit length. Generally speaking, magnetic shielding does not need to be grounded, but it is better to ground in order to prevent electric field induction. When the electromagnetic field passes through the metal or the barrier which attenuates the electromagnetic field, it will be attenuated to a certain extent, that is, it will shield the electromagnetic field. In the actual rectification process, according to the specific needs, choose what kind of shield and shield shape, size, grounding mode and so on.

6. To change the wiring structure of the circuit board, some frequency points are determined by the wiring distribution parameters on the circuit board, so it is not useful to use the above-mentioned method. This kind of rectification changes the circuit parameter structure by adding small inductance, capacitance and magnetic beads in the wiring to move it to the frequency point with higher limit. For this kind of interference, if you want to fundamentally solve its impact, it is necessary to rewire.

The above content is what is the common small method of EMC rectification? have you learned the knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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