EMC Requirements and Test Methods for AC Regulated Power Supplies
Electromagnetic compatibility is an important quality indicator for electrical and electronic products. It can be considered that product quality mainly consists of two aspects: quality specifications and technical indicators. The former involves general specifications, namely IEC internationally and fundamental standards formulated by the state domestically; The latter refers to the specifications of product functions and their technical requirements. Electromagnetic compatibility and basic standards are essential. Now EMC has formed a complete system from basic standards, universal standards, family standards, to product standards. In addition, there is specialized legislation for this internationally. As the European Union has formulated regulations, starting from January 1, 1996, electrical and electronic products must obtain certification for low voltage management (LV Directive) and electromagnetic compatibility management (EMC Directive) before they can be sold in the market. Over the years, new EMC standards have been officially released in China. However, it should be pointed out that IEC's EMC standards will continue to be upgraded from draft or old versions to official versions, and national EMC standards will also be constantly updated and released. EMC testing should be based on the latest version.
The definition of EMC in GB/T4365-1996 "Electromagnetic Compatibility Terminology" is the ability of equipment or systems to operate normally in their electromagnetic environment without causing any unacceptable electromagnetic interference to anything in that environment. This definition summarizes three aspects of content. Firstly, the limitability of electromagnetic interference. Electromagnetic interference is widespread, but its harmfulness can be limited by quality specifications and technical means. This means that a limit on the intensity of electromagnetic interference emitted by the product should be specified to ensure that the electromagnetic environment is qualified. Secondly, the exemption of electromagnetic interference. This means that the product should be able to work normally in an electromagnetic environment with specified electromagnetic interference intensity without reducing its performance indicators. Thirdly, the standardization and compatibility of electromagnetic environment. Any measures taken against electromagnetic interference must not degrade the performance of oneself or other products or systems in the same electromagnetic environment, and can only coexist in a friendly and peaceful manner. For example, in order to reduce conducted interference, capacitors are connected in parallel between the power supply phase line and the ground line of the device. For the equipment, the capacity of the capacitor must meet the limit value requirements for leakage current in the standard; For the system, it is necessary to prevent it from becoming a source of interference coupling that affects the system's operation. Therefore, EMC testing of products should include two main aspects:
(1) Test the electromagnetic interference intensity it sends to the outside world to confirm whether it meets the limit requirements specified in relevant standards;
(2) Conduct sensitivity testing on it under electromagnetic environmental conditions with specified electromagnetic disturbance intensity to confirm whether it meets the anti-interference requirements specified in relevant standards.
