A brief introduction to electromagnetic compatibility in electronic product design

Electromagnetic conduction and radiation emission are the kinetic energy of connecting cables (including power supply) and frequency radiation (RF) emitted according to free space. Governments around the world require the allowable level of such emissions to ensure that the equipment will not cause unreasonable damage to other electronic equipment or affect communication. Therefore, every designer selling electronic products should know some relevant electromagnetic compatibility (EMC) knowledge.

Most industrial and consumer electronic products sold in the United States must meet the requirements of the FCC Regulation TITle47Part15 (generally referred to as FCC Part15) for conducted and radiated emissions. Similar specifications of products sold in Europe are affected by European laws and regulations CISPR22/EN55022. These two sets of regulations also describe the conduction and radiation limits as a function of frequency. Although these two sets of regulations are formulated and managed by different institutions, their construction is similar or similar "coordinated". One advantage of harmonious regulations is that goods designed to conform to one set of regulations can usually ensure that they also conform to the provisions of another set of regulations.

Conducted and radiated emission limits

Conducted radiation specifications include emissions from 15000 kHz to 30 MHz in the frequency range. A set of independent radiation emission standards includes 30 MHz and more frequency bands. The test procedures and tools for conducted and radiated emissions are slightly different. The filter components used to reduce EMC problems are similar, but the electrical values are different. As the conducted emission frequency band is smaller than the radiated emission frequency band, the filter components used to process the conducted emission exceed the needs of processing the radiated emission electrically and physically.

These emissions should be considered. Low frequency (below about 30) MHz) Secondly, conductors and cables of electronic products can transmit RF energy through shared power supply or load, and cause problems in other electronic equipment. However, at various low frequencies, conductors and cables are ineffective as antennas, so radiation at this frequency is generally not a problem. On the other hand, in high frequency (about 30 MHz), the impedance between conductor and cable will fully lose the conduction kinetic energy to avoid them becoming a problem. However, at this higher frequency, conductors and cables can be used as efficient antennas to radiate RF energy, thus affecting nearby electronic equipment.

It is worth noting that no matter whether each subsystem may have conducted all compliance tests, no matter whether each subsystem may have conducted all compliance tests. For example, consider the design and application of many off-the-shelf internal or external power supplies. Although most of the internally assembled power supplies comply with their own design and test requirements, EMC laws and regulations, the test is carried out with separate power supplies. Similarly, the external power supply of wall-plug and desktop versions is mostly designed and tested as a separate module to achieve EMC regulations.

However, after installing the power supply into the system, the system must be tested to ensure that it meets the requirements of EMC. Therefore, although the compliant power supply (or any other subsystem tested in advance) is included in the design, the probability of system test period and EMC-related problems is minimized, but it cannot be guaranteed that the complete system will be tested according to radiation. Therefore, if the power supply customer is a manufacturer that combines power supply and load, it must be tested to ensure that all systems meet the requirements of EMC statutory and take any necessary corrective measures. This will be more interesting than the internally installed power supply, because the circuit is packaged in a closed enclosure, and external components need to be added to solve the EMC problem.

In order to help, many subsystem dealers will provide recommended circuits to solve EMC problems encountered during system integration. Due to the different requirements of each application, the proposal is decided by the designer of the terminal system. In this way, each design only includes the components required for special applications.