table of Contents
1. The concept of EMC
EMC (Electro Magnetic Compatibility)-electromagnetic compatibility refers to the ability of electronic and electrical equipment or systems to work normally in accordance with the design requirements in the expected electromagnetic environment. On a global scale, the issue of electromagnetic compatibility has become a new discipline, and it is also a fringe science based on electromagnetic field theory, including information, electrical engineering, electronics, communications, materials, structure and other disciplines, and it is also a practice. Relatively strong disciplines require product engineers to have rich practical knowledge.
The central topic of electromagnetic compatibility is to study how to control and eliminate electromagnetic interference, so that when electronic equipment or systems work in conjunction with other equipment, it will not cause the deterioration or reduction of the performance of any part of the equipment or system.
An ideally designed electronic device or system should neither emit any undesired energy, nor should it be affected by any undesirable energy. Of course, before an electronic device or system leaves the factory, the main basis for measuring its EMC performance is the EMC test results. These tests are to measure some harassment and interference that a product simulates in the actual working environment, as shown in the following figure:
Generally, the design of electronic products does not consider EMC issues, it will lead to EMC test failure, so that they can not pass the certification of relevant regulations, and can not be sold out of the factory. Even if this product is applied to the actual working environment, some practical problems will arise. Therefore, in practical applications, it is necessary to continuously research practical methods to eliminate electromagnetic interference and disturbance. For example, engineers designed a filter circuit with good effect according to requirements, and placed it in the front stage of the product I/O interface, so that most of the interference noise that enters the system due to conduction can be eliminated in the population of the circuit system; the design Isolation circuits (such as transformer isolation and photoelectric isolation, etc.) solve the conduction interference that enters the circuit through power lines, signal lines and ground lines, and at the same time prevent interference caused by common impedance and long-line transmission; energy absorption loops are designed to reduce Noise energy absorbed by circuits and devices; or by selecting components and rationally arranging the circuit system, the influence of interference can be reduced.
At present, measuring the EMC performance of a product is mainly considered from the following two aspects.
(1) EMI (Electro Magnetic Interference)-electromagnetic interference performance. That is, when the equipment or system in a certain environment is operating normally, it should not produce electromagnetic energy interference that exceeds the requirements of the corresponding standards. Such electromagnetic interference includes:
- Electromagnetic disturbance conducted from the power cord;
- Disturbance conducted from signal lines and control lines;
- Harassment radiated from the product shell (including all cables in the product);
- Harmonic current conducted from the power port (Harmonic);
- Voltage fluctuation and flicker (Fluctuation and Flicker) generated by the power port.
(2) EMS Electro Magnetic Susceptibility)—Electromagnetic immunity performance. That is, when a device or system in a certain environment is operating normally, the device or system can withstand various types of electromagnetic energy interference. This electromagnetic energy interference mainly includes:
- Electrostatic discharge (ESD);
- Electrical fast transient pulse group of power port;
- Electrical fast transient pulse group of signal line and control line port;
- Surge and lightning strike on the power port;
- Surge and lightning strikes on signal lines and control line ports;
- Electromagnetic radiation transmitted from space to the product shell;
- Conducted interference from the power port;
- Voltage drop and interruption of the power port.
EMC design is the use of certain design skills and additional technical means to improve the EMC performance of the product (including the anti-interference ability of the product and the anti-disturbance level of the product) in the product design process, and can follow the product design in a certain environment Expect normal operation. In order to measure the EMC performance of the product before it reaches the actual application environment, an EMC test is required. Corresponding to the EMC indicators of the above products, EMC testing usually has the following two aspects.
(1) EMI electromagnetic interference test
- Power line conducted disturbance (CE) test;
- Signal and control line conduction disturbance (CE) test;
- Radiated disturbance (RE) test;
- Harmonic current (Harmonic) test;
- Voltage fluctuation and flicker (Fluctuation and Flicker) test.
(2) EMS electromagnetic immunity test
- Electrostatic discharge (ESD) immunity test;
- Electrical fast transient pulse group (EFT/B) immunity test of power port;
- Electrical fast transient pulse group (EFT/B) immunity test of signal lines and control lines;
- SURGE and lightning test of power port;
- SURGE and lightning test of signal lines and control lines;
- Shell radiation immunity (RS) test;
- Conducted immunity (CS)) test of power port;
- Conduction immunity (CS) test of signal lines and control lines;
- Voltage drop and interruption test (DIP) of the power port.
2. EMC design concept
In the design of electronic products, in order to obtain good EMC performance and cost ratio, it is important to carry out EMC design on the product.
The EMC performance of electronic products is given by design. The test only uses a certain quantitative method to characterize the inherent EMC performance of electronic products. For enterprise standardized EMC design, it can be implemented in the following three steps.
Step 1: EMC design should be considered in the early stage of research and development.
If the EMC problem is not considered in the early stage of product design, only hope to solve it in the test stage (indicated by solving the EMC problem of the designed product through rectification, so a lot of manpower and material resources are invested in the later stage of testing/verification and rectification). Then, even if the product rectification is successful, in most cases, the rectification involves changes in circuit principles, PCB design, and structural molds, which will greatly increase R&D costs and greatly extend the cycle.
Only by considering and predicting EMC issues in the pre-product design process, turning EMC into a controllable design technology, paralleling and synchronizing with the process of product function design, can the product be designed at once.
Step 2: Improving the EMC performance of electronic products through design is definitely not given by EMC experts in the enterprise alone, because EMC is absolutely impossible to exist without product hardware, structure and other physical objects.
Therefore, to make the designed electronic products achieve good EMC performance at one time, it is necessary to improve the EMC experience and awareness of product design engineers. For example, hardware engineers should master the basic knowledge of EMI and EMS anti-interference design in addition to the circuit design knowledge that they must master before; PCB design engineers need to master the corresponding device layout, stacking design, and high-speed wiring EMC design knowledge; structural engineers Also need to understand the design knowledge of product structure shielding.
Because these engineers who participate in the product design together, in order to realize the opinions put forward by EMC experts in the product design process, they must understand and comprehend the mystery of the suggestions put forward by EMC experts, and combine them with the design characteristics of their respective fields to combine all The germination of EMC problems is eliminated in the product design stage. Only all the developers involved in product design can improve EMC quality together to design electronic products with high performance EMC.
Step 3: The enterprise must establish a set of standardized EMC design system and design analysis method by itself.
Enterprises should establish a set of standardized EMC design system and design analysis methods, that is, integrate the process of EMC design analysis and risk assessment in the research and development process, carry out EMC evaluation and analysis control at all stages of product design, and take the possible EMC The problem is considered in the early stage of research and development, and the risk of failure of EMC testing is predicted.
Fully consider the possible EMC problems in the early stage and find a solution to ensure that the product can pass the test and certification at one time after the product design. Of course, for companies, this will also reduce unnecessary manpower and R&D costs, and shorten the product launch cycle.