Analysis of the design of the electromagnetic compatibility of switching power supply systems
With the rapid development of electronic technology, electronic devices are also moving towards functional integration and miniaturization, which brings us many conveniences. However, the electromagnetic coupling between various electronic devices has also become the main problem faced by engineers. The harm of electronic environmental pollution is no less than that of traditional environmental pollution. Electromagnetic pollution, as a part of environmental pollution, has also been put on the agenda. Electronic devices can withstand various electromagnetic interferences during normal operation, including mutual interference from their internal components and interference from other electronic devices around them. At the same time, they can cause electromagnetic interference to other electronic devices around them. The requirements for electronic devices vary greatly in different application environments (household, industrial control, and power). In this regard, reference can be made to the general standard IEC/EN61000-6 series or the industry requirements of corresponding products.
This type of electromagnetic interference mainly includes two aspects in terms of transmission pathways: first, transmission along the wiring harness, which mainly includes transmission along the power port and signal port; On the other hand, it mainly involves transmission along space.
1. Electromagnetic interference:
The power supply must meet the corresponding minimum emission energy requirements in its application environment, otherwise it will interfere with the surrounding equipment. According to the requirements of general types, the standard IEC/EN61000-6 is divided into industrial environment equipment requirements and residential, commercial, and light industrial environment emission requirements; For general products such as power supplies, unless it is a special model, electromagnetic interference positioning will be carried out according to IEC/EN61000-6-3 or IEC/EN61000-6-4 during the initial design stage.
With the continuous miniaturization of power supply volume and the increasing power density, the difficulty of designing electromagnetic interference for the power supply itself continues to increase. Currently, all AC-DCs on the market of MORNSUN not only have built-in filters, but also invest a lot of design costs in transformer shielding and power device noise absorption, meeting the promised indicators; The R2 generation low-power DC-DC products are all designed with a six sided shielding structure, meeting the class A requirements of EN55022/CISPR 22 and EN55011/CISPR 11 in the industry, and meeting the level requirements of basic industries.
Although significant design costs have been invested in the electromagnetic interference of the power supply itself and it meets the promised indicators, it is still inevitable that the power supply will encounter issues of excessive electromagnetic interference in market applications; At this point, many design engineers may believe that the root cause of the problem lies in the power supply. However, there is a misconception in this regard, because electromagnetic interference conducted interference testing projects mainly target the power supply port, and the power supply port becomes its transmission path. All electromagnetic interference will reach the tested equipment through the power supply port. However, the electromagnetic interference detected by the testing equipment not only comes from the power supply itself, but also from other parts of the entire machine, as well as the electromagnetic interference generated by resonance of parasitic parameters inside the equipment. This type of electromagnetic interference will be coupled to the testing equipment through the power supply port, and the internal filter of the power supply cannot filter this part of electromagnetic interference. The application environment of the power supply varies greatly, All power supply design filters are designed with the primary consideration of solving their own interference. At the same time, the attenuation characteristics and spectral characteristics of the filters should be reserved to the maximum extent possible, but it is not possible to be compatible with all application scenarios; So this requires our whole machine designers to design the power supply front-end according to the application circuit recommended by the power supply manufacturer, for example, if there is EMI exceeding the standard during the application process of LH15 products.
