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EMC/EMI integrated solution and design experience sharing - Power Circuit - Circuit Diagram
As electronic and electrical technologies continue to evolve, household appliances are becoming increasingly popular and electronic. The rapid advancement of radio, television, telecommunications, and computer networks has created a more complex and challenging electromagnetic environment. This has heightened our awareness of the importance of the operating environment for equipment and the impact of electromagnetic interference (EMI) and compatibility (EMC) on electronic devices. Engineers and manufacturers are placing greater emphasis on these aspects. To assist designers and engineers in addressing EMC/EMI challenges during product development and application, the Electronic Component Technology Network has successfully hosted seven sessions of EMC technology seminars, featuring experts who discussed market trends, technological advancements, and cutting-edge applications in the field of EMC/EMI. These talks provided valuable insights into overcoming design challenges and ESD protection issues encountered in practical scenarios. Below is a summary of the key technical highlights from previous EMC/EMI seminars.
At the 7th Circuit Protection and Electromagnetic Compatibility Symposium held at the Shenzhen Convention and Exhibition Center on April 8th, numerous domestic and international leading manufacturers presented solutions for EMC/EMI. The following are excerpts from the expert presentations:
Dr. Zhao Yang, Chief Engineer at Suzhou Taisite Electronic Technology Co., Ltd.: "Comprehensive Solution for Electromagnetic Compatibility Issues" (Click to download the presentation slides)
Renowned expert and respected teacher Tao Xianfang: "Experience Sharing for EMC Design Engineers" (Click to download the presentation slides)
Fan Weijun, Senior Product Engineer at Murata (China) Investment Co., Ltd.: "EMC Solutions for Enhancing Mobile Phone Sensitivity" (Click to download the presentation slides)
Static electricity protection (ESD) plays a crucial role in identifying protected components. When designing electromagnetic protection circuits, engineers must clearly understand what elements within the system require protection. Identifying which of the thousands of devices are critical and susceptible to interference is essential. Once the protected circuits are identified, electrostatic analysis should commence. What type of static electricity causes malfunctions? What are the underlying reasons? After analyzing various factors, appropriate electrostatic protection measures should be implemented, selecting suitable devices. Dr. Zhao Yang emphasized this in his comprehensive solution for electromagnetic compatibility issues.
Conductive ESD Protection: The primary method involves using protective devices like ceramic capacitors, varistors, and TVS diodes to form a protection circuit at the front end of sensitive components. These devices guide or dissipate current to prevent damage.
Radiation ESD Protection: Static electricity fields can impact sensitive circuits. The protection strategy focuses on minimizing the generation and energy of these fields while enhancing structural improvements to safeguard sensitive lines. A method known as equipotential bonding is often employed in practice. By effectively creating a casing that forms the same potential, discharges are suppressed. This approach has proven effective and straightforward to implement.
General ESD Protection Methods:
1. Reduce static electricity accumulation.
2. Insulate products to prevent static electricity generation.
3. Provide branches to shunt electrostatic currents away from sensitive lines.
4. Shield circuits in discharge areas.
5. Minimize loop areas to protect circuits from magnetic fields generated by static discharge.
From the perspective of electromagnetic induction, Circuit Protection and Electromagnetic Compatibility expert Teacher Tao Xianfang suggests that a high-quality electronic product not only excels in functionality but also demonstrates superior circuit design (ECD) and electromagnetic compatibility design (EMCD). The quality and technical proficiency of a product's performance indicators play a significant role. While many individuals engage in electronic circuit design, starting with a foundational understanding of electronic components, they often struggle when transitioning to electromagnetic compatibility design. In reality, EMC design begins with electromagnetic field theory, specifically from the knowledge of electromagnetic induction. Consider that when multiple electronic devices operate in the same space, they generate electromagnetic fields of varying intensities around them. These fields may interact with each other, causing instability or crashes—electromagnetic interference (EMI) is the culprit. EMI is prevalent in electronic products, occurring between devices, components, systems, and subsystems. The two main forms of interference are conducted and radiated interference, with conducted interference further subdivided into common-mode and differential-mode interference. The root cause of interference is electrostatic discharge. Ensuring system stability without external influences involves a three-step process aimed at comprehensively solving electrostatic discharge interference to enhance design efficiency. Three key strategies to mitigate radiation interference include shielding, reducing the area of current loops (to combat magnetic field interference), and minimizing the area and length of live conductors (to address electric field interference).
When the length of the conductor matches an integral multiple of the quarter-wavelength of the interference signal, resonance occurs in the circuit, resulting in maximum radiation interference. This situation should be avoided whenever possible. Magnetic field radiation interference primarily arises from the magnetic flux generated by high-frequency current loops flowing into receiving loops. Thus, minimizing the area of these loops is critical.
Common EMI suppression methods currently include shielding, spread spectrum techniques, and filtering. Most electromagnetic shielding methods are employed to block noise above 300 MHz. Additionally, using composite materials for masking is another common approach. For instance, mobile phones often undergo vacuum plating, with a plastic shield covered by a nickel layer to prevent electromagnetic wave divergence. The spread spectrum technique disperses the clock (Clock) signal to reduce the amplitude of the peak signal waveform, thereby lowering the signal's peak level. Some BIOS versions offer built-in spread spectrum functionality, enabling users to configure settings themselves. Xiaotong Yu noted that achieving a balance between signal distortion and EMI attenuation is essential when using spread spectrum techniques, typically ranging from 1% to 1.5%. Exceeding 3% often results in excessive signal distortion, rendering the method impractical. Filters or filter loops are commonly used by design engineers due to their low cost and ease of implementation via surface mount technology (SMD). Filter opportunities and modes depend on specific control requirements. For example, a large current bead can be used on power traces (Power Trace); a general bead can suppress specific frequency noise signals; CMF is used to address USB differential mode line noise radiation problems, among others like 1394 and LVDS. However, selecting the right EMI suppression solution requires careful consideration based on the specific scenario, ensuring effectiveness rather than adhering strictly to any one method.
Radiation conduction EMI remains a challenging issue, with solutions including:
1. Adding an LC filter circuit to the interference source.
2. Introducing noise into the ground via bypass capacitors on the I/O side.
3. Encasing electromagnetic waves with shielding.
4. Expanding the PCB area where possible.
5. Minimizing the use of flat cables or solid wires within the product.
6. Twisting internal physical wires to suppress noise radiation, adding bypass capacitors to the I/O end of flat cables.
7. Adding a common mode filter at the beginning or end of differential mode signal lines.
8. Following specific analog and digital wiring principles.
EMI formation can be categorized into two types: common mode radiation and differential mode radiation. Common mode radiation encompasses common mode interference from ground impedance and electromagnetic field interference to the wires. The former results from shared grounding resistance between noise sources and victim circuits, mitigated by avoiding common interference problems. The latter involves interference caused by high electromagnetic energy fields affecting device wiring, addressed through shielding and isolation methods. Differential mode radiation refers to differential mode interference between wires. The interference path involves noise infecting other wires and feeding into victim circuits, a near-field interference issue resolved by widening the distance between lines.
Four major solutions to enhance mobile phone sensitivity were proposed in "EMC Solutions for Improving Handset Sensitivity" by Murata experts. Modern electronic products are evolving towards higher performance, leading to complex changes in electronic devices. For example, mobile phones feature decreasing IC operating voltages, reduced energy, and faster interface communication speeds. Additionally, the increasing number of electronic controls in automotive applications has made our electronic designs more intricate. This trend demands greater attention to EMC/EMI considerations. We anticipate these demands will grow as technology advances.
Electromagnetic compatibility standards, as defined by IEC, fall into three categories: basic standards, general standards, and product-specific standards. Basic standards are further divided into emission standards and immunity standards. General standards categorize environments into Classes A and B. Class A pertains to industrial zones, while Class B relates to civilian use. Therefore, it is crucial to identify the exact standards applicable to your product. For a given product, if no specific product EMC standard or applicable product class EMC standard exists, the general EMC standard should be adopted, with a preference for product-specific standards. If no applicable EMC standard or product class standard is available, a general standard should be used.
Shou Jianxia, Secretary General of the National Radio Interference Standardization Technical Committee, discussed the latest international and domestic electromagnetic compatibility standards, recent developments, and testing industries during Circuit Protection and Electromagnetic Compatibility in Shanghai. He also touched upon industry associations and national standardization committees, addressing all recognized electromagnetic compatibility issues in laboratories.
In Circuit Protection and Electromagnetic Compatibility in Chengdu, the Electronic Component Technology Network invited European EMC technology and standards expert Dr. Gerd Jeromin to discuss European radio and communication equipment EMC challenges, system solutions, methods, European standards, and testing, focusing on EMC technology hotspots. Click to view: Trends in EMC Standards and Wireless Communication Device Planning and Application.
The technical highlights of the 7th Circuit Protection and Electromagnetic Compatibility Symposium, held at the Shenzhen Convention and Exhibition Center on April 8th, included presentations from renowned experts and manufacturers addressing EMC/EMI solutions. Dr. Zhao Yang, Chief Engineer at Suzhou Taisite Electronic Technology Co., Ltd., shared insights on comprehensive solutions for electromagnetic compatibility issues. Renowned expert Tao Xianfang offered experience sharing for EMC design engineers. Fan Weijun, Senior Product Engineer at Murata (China) Investment Co., Ltd., presented solutions for enhancing mobile phone sensitivity. These discussions provided valuable perspectives on addressing EMC/EMI challenges in product design and application.