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EMC design of the three laws and what are the three elements, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can gain something.

Three laws of EMC

1) Law 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.

Experience 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.

2) Law 2. The larger the high frequency current loop area 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.

3) Law 3. The higher the loop current frequency f, the more serious the EMI radiation, 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 following content of this paper is to make use of the above three laws, advocate to consider the EMC problem as soon as possible, and introduce the EMC design and the improvement of EMC problems.

Improving EMC problems is like diagnosing and treating diseases. If the product does not pass the EMC test, we can only know which frequency points "exceed the standard" from the measurement results, and where the electromagnetic interference of these frequencies comes from is often the most difficult problem for engineers to find and solve. When it comes to the problem of product EMC, it is difficult to say, easy to say.

To improve the EMC problem, first of all, according to the way and mechanism of EMI, that is, the elements of EMC problem, according to the circuit principle of EUT (tested sample, the same below), first make some judgments, such as the cause of EMC problem caused by IT equipment and AV audio and video equipment or what the internal disturbance source is, first infer, then combined with the test project test chart to see the essence through the phenomenon. Analyze the reasons for the difference-find out the source of harassment and find out the ways of harassment thoroughly in order to have a clear target.

To analyze the causes of the error, we can use a high-frequency oscilloscope or spectrum analyzer plus a field probe to verify the analysis results, from frequency domain to time domain, and then from frequency domain to time domain, to analyze and find the corresponding circuits and devices that cause EMC problems.

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 the power line or affects the connected equipment through other terminals (such as radio frequency terminals, input terminals).

Conduction, radiation, disturbance source-(pathway)-sensitive receptor near field coupling IT, AV equipment possible disturbance source

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 pulses and high-order harmonics of switching power supplies, square waves and high-frequency harmonics of synchronous signals, line and field signals and high-frequency harmonics generated by line-scanning imaging circuits

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 of digital signal and high frequency harmonic, high order harmonic produced by crystal oscillator, useless signal and stray signal 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.

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