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This article will explain in detail what are the three basic elements of solving the EMC problem of electromagnetic compatibility. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

EMC is a difficult point in the industry; let's talk about the three laws of EMC, the three elements of EMC, the characteristics of electromagnetic disturbance, and the five-level EMC design method.

The improvement of EMC should treat the disease the same as the diagnosis and treatment of diseases; we advocate adhering to the law of EMC and considering and solving the EMC problem as soon as possible-EMC design. Let's recognize the following three elements and three important laws in the field of EMC:

Three elements of EMC problem

Switching power supply and digital equipment will produce strong radiation because of the rich high-frequency harmonics of pulse current and voltage. Electromagnetic interference includes radiant (high frequency) EMI and conductive (low frequency) EMI, that is, the problem of EMC is mainly caused by two ways: one is in the form of space electromagnetic wave interference, the other is in the form of conduction, in other words, the three elements of EMC problem are: electromagnetic interference source, coupling path, sensitive equipment. Radiation interference mainly pollutes the space electromagnetic environment in the form of electromagnetic waves through the shell and connection lines; conducted interference disturbs the public power grid through power lines or affects connected equipment through other terminals (such as radio frequency terminals, input terminals).

Possible sources of harassment for IT and AV devices

A) the FM receiver and TV receiver oscillate locally, and the fundamental and harmonics are generated by the high frequency head and the local oscillation circuit

B) switching pulse and high-order harmonics of switching power supply, square wave and high-frequency harmonics of synchronous signal, line and field signals and high-frequency harmonics generated by line-scanning imaging circuit.

C) all kinds of clock signals and high frequency harmonics needed for digital circuit operation, and their combinations, various clocks such as CPU chip working clock, MPEG decoder working clock, video synchronous clock (27MHz 40.5MHz 16.9344MHz), etc.

D) Square wave and high frequency harmonics of digital signal, high order harmonics produced by crystal oscillator, useless signals and stray signals caused by nonlinear circuit phenomena (nonlinear distortion, Intermodulation, saturation distortion, cut-off distortion), etc.

E) non-sinusoidal waveform, waveform burr, overshoot, ringing, parasitic frequency point in circuit design.

F) external disturbances to sensitive receptors through the coupling pathway include surges, fast pulse groups, static electricity, voltage sags, voltage changes and various electromagnetic fields.

Characteristics of electromagnetic disturbance

The spectrum of ① unit pulse is the widest.

The low frequency content in the ② spectrum depends on the area of the pulse, and the high frequency component depends on the steepness of the front and rear edge of the pulse.

The oscillation level of ③ crystal must meet a certain amplitude before the digital circuit can work in a certain time sequence, so that the disturbance caused by crystal oscillator has the characteristics of covering bandwidth and high disturbance level.

When the polarization and directional characteristics of ④ transceiver antennas are the same, the radiation and reception of EMI are the most serious, and the larger the area of EMI transceiver antenna is, the greater the harm of EMI is.

⑤ harassment pathway: the combination of radiation, conduction, coupling and radiation, conduction and coupling.

The conducted disturbance of ⑥ power cord is mainly caused by common mode current.

The radiation disturbance of ⑦ is mainly caused by the loop formed by differential mode current.

Three important laws of EMC

Rule 1. The law of EMC cost-effectiveness ratio: the earlier the EMC problem is considered and solved, the smaller the cost and the better the effect.

In the new product research and development stage to carry out EMC design, than wait until the product EMC test is unqualified to improve, the cost can be greatly saved, the efficiency can be greatly improved; otherwise, the efficiency will be greatly reduced and the cost will be greatly increased.

The test tells us that it is the most time-saving and most cost-effective to carry out EMC design at the same time of functional design and pass the EMC test when the template and prototype are completed. On the contrary, the product research and development stage does not consider EMC, after putting into production, it is found that EMC is unqualified before improvement, which not only brings great technical difficulty, but also rework will inevitably lead to a great waste of cost and time, and even due to structural design, PCB design defects, can not implement improvement measures, resulting in products can not be on the market.

Second, the larger the area of high frequency current loop S is, the more serious the EMI radiation is.

The high frequency signal current flows through the minimum path of the inductor. When the frequency is high, the general line reactance is greater than the resistance, the connection to the high frequency signal is the inductor, and the series inductor causes radiation. Most of the electromagnetic radiation is produced by the high-frequency current loop on the EUT test equipment, and the worst case is in the form of open-circuit antenna. The corresponding processing method is to reduce and shorten the connection, reduce the area of high-frequency current loop, and eliminate any abnormal antennas as far as possible, such as discontinuous wiring or long pins of components with antenna effect.

One of the most important tasks to reduce radiation disturbance or improve the anti-jamming ability of radio frequency radiation is to find ways to reduce the high frequency current loop area S.

Rule 3. The higher the loop current frequency f is, the more serious the EMI radiation is, and the electromagnetic radiation field intensity increases proportional to the square of the current frequency f.

The second most important way to reduce radiation disturbance or improve the anti-jamming ability of radio frequency radiation is to find ways to reduce the high frequency current frequency f of the disturbance source, that is, to reduce the frequency f of the disturbance electromagnetic wave.

The three elements of the EMC problem and understanding the three laws of EMC will make the EMC problem have rules to follow. Adhering to the law of EMC will save time and effort to solve the EMC problem and get twice the result with half the effort.

On solving the electromagnetic compatibility EMC problem what are the three basic elements are shared here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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