EMC/EMI integrated solution and design experience sharing - Power Circuit - Circuit Diagram

With the development of electrical and electronic technology, the increasing popularity and electronicization of household electrical appliances, the increasing development of radio and television, postal and telecommunications, and computers and their networks, the increasingly complex and deteriorating electromagnetic environment has led us to pay more attention to the working environment of equipment and to pay more attention to electromagnetics. The impact of the environment on electronic equipment, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) of electrical and electronic products are increasingly being valued by engineers and manufacturers. In order to help engineers and engineers solve the EMC/EMI problems encountered in product design and application, Electronic Component Technology Network has successfully held seven sessions of EMC technology seminar, inviting experts in the field of EMC/EMI to explain their market and technology trends. And frontier applications, there are more on-site questioning sessions, discussing with experts the EMC/EMI design challenges and ESD protection encountered in the actual design. This half-month talk summarizes the technical highlights of previous EMC/EMI seminars.

At the 7th Circuit Protection and Electromagnetic Compatibility Symposium held at the Shenzhen Convention and Exhibition Center on April 8th, many leading domestic and foreign manufacturers published solutions for EMC/EMI. The following are the contents of the lectures and presentations of the experts. Download address:
Dr. Zhao Yang, Chief Engineer of Suzhou Taisite Electronic Technology Co., Ltd.: "Comprehensive Solution for Electromagnetic Compatibility Issues" (click to download the speech PPT)
Well-known expert, community good teacher Tao Xianfang: "Design Engineer EMC Experience Sharing" (click to download the speech PPT)
Fan Weijun, Senior Product Engineer, Murata (China) Investment Co., Ltd.: "EMC Solution for Improving Cell Phone Sensitivity" (click to download the speech PPT)

Electrostatic protection (ESD) is important to find protected objects. In designing electromagnetic protection circuits, engineers need to know clearly what to protect in the system. It is important to find protected objects. How do you find out which of the 10,000 devices are core and which are susceptible to interference? When the protected circuit is found, it is necessary to start electrostatic analysis. Which kind of static electricity makes it invalid? what is the reason? After analyzing various reasons, it is necessary to carry out electrostatic protection measures and select the corresponding device. Dr. Zhao Yang mentioned in the comprehensive solution for electromagnetic compatibility issues. Conductive ESD protection: The protection of electrostatic current in the circuit mainly uses some protection devices, which form a protection circuit at the front end of the sensitive device to guide or dissipate current. Such protection devices are: ceramic capacitors, varistors, TVS tubes, etc.
Radiation ESD protection: The field generated by static electricity has an impact on sensitive circuits. The protection method is mainly to minimize the generation and energy of the field, improve the protection ability through the improvement of the structure, and protect the sensitive lines. The protection of the field is often difficult, and a method called an equipotential is explored in the practice of improvement. By effectively erecting, the casing forms the same potential and suppresses discharge. This has proven to be effective and easy to implement.
General method of protection against static electricity (the first three are for direct discharge and the last two are for coupling of associated fields)

• Reduce the accumulation of static electricity;
• Insulate the product to prevent static electricity from occurring;
• Providing a branch shunting electrostatic current to the sensitive line;
• Shielding the circuit in the discharge area;
• Reduce the loop area to protect the circuit from the magnetic field generated by electrostatic discharge.

From the understanding of electromagnetic induction, the electromagnetic compatibility design community teacher Tao Xianfang believes that: a good electronic product, in addition to the product's own functions, the technical level of circuit design (ECD) and electromagnetic compatibility design (EMCD), the quality and technology of the product. Performance indicators play a very important role. Many people are engaged in the design of electronic circuits, starting with the understanding of electronic components, but when they are engaged in electromagnetic compatibility design, they have no way to start. In fact, the electromagnetic compatibility design starts from the electromagnetic field theory, that is, from the electromagnetic induction knowledge. Imagine that when multiple electronic devices work in the same space, they will generate electromagnetic fields of a certain intensity around them, and they may be present or artificially Interference can interfere with equipment through conduction, radiation, etc., making the system unstable and even crashing - the culprit is electromagnetic interference. Electromagnetic interference is common in electronic products. It is not only the interaction between devices, but also between components and components. Between the system and the system, the two main ways are conducted interference and radiated interference, and conducted interference Subdivided into common mode interference differential mode interference. The causes of interference are complex, and the core is electrostatic discharge interference. How to ensure the stable operation of the system without external influence? The following is a three-step rule for the electronic component technology network to provide you with a necessary book to completely solve the electrostatic discharge interference to improve design efficiency. Three major countermeasures to reduce radiation interference: one is shielding, the other is to reduce the area of ​​each current loop (magnetic field interference), and the area and length of the live conductor (electric field interference). 2. When the length of the carrier fluid is exactly equal to an integral multiple of the quarter-wavelength of the interference signal, the interference signal will resonate in the circuit. At this time, the radiation interference is the strongest, and this situation should be avoided as much as possible. 3. Magnetic field radiation interference is mainly caused by the magnetic flux generated by the high-frequency current loop flowing into the receiving loop. Therefore, the area flowing through the high-frequency current loop and the area of ​​the receiving loop should be minimized. Common EMI suppression methods Currently, common suppression methods for EMI include Shielding, Spread Spectrum, Filter, etc., and control through integrated grounding, wiring, and lap joints. Most of the electromagnetic shielding method is used to shield electromagnetic noise above 300MHz. In addition, the use of masking composite materials is also a common method. For example, mobile phones are often vacuum-plated, and a plastic shield is covered with a shield such as nickel. Material to isolate electromagnetic waves from divergence. The spread spectrum rule is used to spread the signal of the clock (Clock) to reduce the amplitude of the peak signal waveform to reduce the peak level of the signal. Some BIOSes now provide built-in spread spectrum function, allowing users to make their own set up. Yu Xiaotong pointed out that the use of spread spectrum method needs to strike a balance between signal distortion and EMI attenuation, which is generally 1% to 1.5%. If it exceeds 3%, it will usually make the signal too distorted and not feasible. The use of filters or filter loops is the most common design engineer's use because of the low cost and processing requirements of SMD (surface mount) processes. Filter opportunities and modes are determined according to different control requirements. For example, a large current Bead can be used on the power trace (Power Trace); a general Bead can be used to suppress a specific frequency noise signal; CMF is used to suppress USB Noise radiation problems of differential mode lines such as 1394 and LVDS. However, there are many solutions to the suppression of EMI. It must be chosen according to local conditions. As long as it is effective, it is a good method of prevention. There is no specific way to win.

The radiation conduction EMI is a tough problem, and the solution can be summarized as follows:

1. Add an LC filter circuit to the interference source. 2. Add DeCap by pass to Ground to the I/O side to introduce noise into the ground. 3. Wrap electromagnetic waves in the shield with Shielding. 4. Try to expand the PCB area. 5. Use flat cables or solid wires as little as possible inside the product. 6. The physical wires inside the product are twisted as much as possible to suppress noise radiation, and DeCap is added to the I/O end of the flat cable. 7. Add a Common Mode Filter to the beginning or end of the differential mode signal line. 8. Follow certain analog and digital wiring principles. In addition, the formation of EMI can be divided into two types: common mode radiation and differential mode radiation. The common mode radiation includes the common mode interference of the common ground impedance and the common mode interference of the electromagnetic field to the wire. The former is the common mode interference caused by the same grounding resistance shared between the noise generating source and the victim circuit, and the solution can be implemented by The cutting must avoid the common interference problem; the latter is the interference caused by the electromagnetic field formed by the high electromagnetic energy to the wiring between the devices, and the field-to-line interference problem can be handled by the method of shielding the isolation. As for differential mode radiation, the common mode is the differential mode interference of the wire to the wire. The interference path is that the interference noise in a certain wire is infected into other wires and fed into the victim circuit, which is a kind of near-field interference, which can be widened by The distance between the lines to handle such interference problems.

EMC's four major solutions to improve handset sensitivity In the "EMC solution for improving handset sensitivity", Murata experts proposed that electronic products are now developing with high performance, which leads to complex changes in electronic devices. For example, mobile phones, its IC working voltage is getting lower and lower, energy is getting smaller and smaller, and smartphones, including PCs and wireless circuits, will have a related interference. The third is the speed of interface communication is getting higher and higher. The fourth is the increasing number of electronic controls in automotive applications. These have made our electronic version more and more complex, which has made our approach more and more important. We believe that this change will become more and more demanding as it changes. Electromagnetic products market, safety and testing trends Electromagnetic compatibility standards In fact, IEC is divided into three categories: basic standards, general standards and product standards. The basic standards are divided into emission standards and immunity standards. The general standard divides the environment into two categories: A and B. Class A belongs to the industrial zone, and class B is civil. Therefore, we should know which one is the indicator you really want to achieve. For a product, if there is neither a product EMC standard nor a applicable product class EMC standard, the general EMC standard should be adopted. A product standard is preferred, and then the product standard is up to you. For a product, if we do not have an EMC standard and do not have an appropriate product class standard, we use a common standard. Shou Jianxia, ​​Secretary General of the National Radio Interference Standardization Technical Committee, in Circuit Protection and Electromagnetic Compatibility. Shanghai Station introduced the latest international and domestic electromagnetic compatibility standards, recent developments and testing industry, involving industry associations and national standardization committees. All electromagnetic compatibility issues recognized by the laboratory.

In circuit protection and electromagnetic compatibility. Chengdu station, electronic component technology network also invited European EMC technology and standards expert Dr. Gerd Jeromin to focus on the European radio and communication equipment EMC challenges, system solutions and methods, European standards and testing, etc. EMC technology hotspots. Click to watch: EMC standards and wireless communication device planning and application trends.