EMC rectification

Introduction of relevant rectification

EMC mainly includes two major parts: EMI and EMS.

EMI

RE、CE、Harmonic 、Flicker

EMS

ESD 、EFT、DIP、CS、RS、Surge、PFMF

Rectification suggestion

Provide enterprises with fast, efficient, and low-cost rectification solutions

Rectification idea

Considering the overall situation from the perspective of the product system, through detailed analysis of the product schematic diagram, PCB, and structure, we can solve the EMC problem of the product from the source.

Conclusion

Strengthening EMC management during product design and production can effectively reduce the workload of later rectification and improve the electromagnetic compatibility of products.

 

Analysis of common electromagnetic compatibility rectification problems

Rectification methods:

EMC electromagnetic compatibility rectification can be carried out from the following ideas:

Reduce sources of interference

Find the source of interference and reduce the interference within the allowable range.

Dealing with line-to-line coupling in wires and cables

Because of the frequency factor, when the wire length is equal to or less than 1/16 wavelength, the physical model is low-frequency coupling with capacitive coupling. Therefore, the main purpose of rectification is to reduce the distributed coupling capacitance or reduce the coupling amount.

High-frequency coupling refers to traces longer than 1/4 wavelength. Due to the presence of standing waves of voltage and current in the circuit, the amount of coupling will be enhanced.

Electromagnetic shielding

It can effectively suppress various electromagnetic interferences in space propagation. According to the mechanism, it can be divided into multiple types of shielding, which requires more attention.

Change the wiring structure of the circuit board

This method generally starts from the frequency point of the circuit board. This type of rectification changes the circuit parameter structure by adding small inductors, capacitors, and magnetic beads in the wiring to move it to a frequency point with higher limit requirements.

 

Common rectifications

 

• EMI exceeds the standard: Electromagnetic interference may come from electronic components, circuit layout, cable routing, etc. inside the product. Rectification measures usually include optimizing circuit design, adding filter components, improving grounding systems, etc.

 

• Insufficient EMS: that is, the product cannot work normally or its performance degrades when subjected to external electromagnetic interference. The anti-interference ability of the product can be improved, such as adding shielding measures, optimizing power supply design, etc.

 

• Test failure: When conducting EMC testing, the test may fail due to various reasons. This may be related to testing equipment, testing methods, whether there are defects in the product itself, etc. During rectification, the test data should be carefully analyzed to find out the reasons for the failure and take corresponding measures.

Tips:

Take the rectification of radiation harassment as an example:

Products with excessive radiation harassment may cause the performance of surrounding devices, equipment or systems to degrade or cause damage to living or inanimate substances. The rectification must be qualified and meet the requirements of relevant laws and regulations before the product can enter the market smoothly.

 

The general rectification process is as follows:

1. Understand the product characteristics, frequency points where radiation harassment exceeds the standard, and analyze the sources of interference;
2. Understand the working principle of the main chip in the schematic diagram, and analyze the disturbance sources of oscillation signals and high-frequency signals;
3. Combine the layout and schematic diagram to analyze whether the impedance circuit and peripheral circuits match, and eliminate existing interference sources;
4. Independently test by mode and compare the data to eliminate the interference caused by each mode and narrow the scope of rectification;
5. Find the source of interference, take appropriate measures, and make rectification;
6. Verify the rectification effect.

 

Generally, two rectification methods are supported: one is for customers to go to the site for rectification. Because customers know their products better, they can come to the site to adjust some ground capacitance and resistance or add common mode inductors. The second is for us to help with rectification. Without damaging the circuit, we can consider wrapping copper foil or conductive cloth on the interface that is considered to have signal interference, adding a magnetic ring to the power line, etc.

 

Rectification tips:

1. Design appropriate shielding structures and shielding materials to reduce electromagnetic radiation;
2. Optimize PCB layout and reduce the length and crossover of signal lines;
3. Use appropriate filters to suppress high-frequency noise;
4. Control the grounding of the equipment and ensure a good ground connection;
5. Optimize power wiring and reduce common-mode interference on power lines;
6. Use appropriate ground loops to reduce interference between loops;
7. Use a shield or metal box to encapsulate sensitive circuits;
8. The high-frequency signal interface should consider adding a filter or isolator to shield the signal;
9. During PCB core layout, the circuit loop composed of large electrolytic capacitors, transformers, MOS, etc. should be as small as possible;
10. When designing the PCB, the loop composed of the output diode and the output smoothing electrolytic capacitor should be as small as possible.

 

Summarize

Interference: eliminate interference sources, cut off the interference conduction paths, and divert interference sources;

Anti-interference: improve the shielding of the shell and optimize the circuit board design to improve the anti-interference ability.