Electromagnetic Compatibility Design Analysis of Power System
Electromagnetic Interference:
The power supply must meet the corresponding minimum emission energy requirements in its application environment, otherwise it will cause interference to the equipment in the surrounding environment. The standard IEC/EN61000-6 is divided into industrial environment equipment requirements and residential area, commercial Emission requirements in areas and light industrial environments; for general-purpose products such as power supplies, the electromagnetic interference positioning at the initial design stage will be designed in accordance with IEC/EN61000-6-3 or IEC/EN61000-6-4 unless it is a special model.
With the continuous miniaturization of the power supply and the continuous increase of power density, it is increasingly difficult to design the electromagnetic interference of the power supply itself. At present, all AC-DCs on the market of MORNSUN not only have built-in filters, but also in terms of transformer shielding, A large amount of design cost has been invested in the noise absorption of power devices to meet the promised index requirements; R2 low-power DC-DC products are all designed with a six-sided shielding structure, meeting the CLASS A of the industry EN55022/CISPR 22 and EN55011/CISPR 11 Requirements, in line with the level requirements of the basic industry.
Although a lot of design cost has been invested in the electromagnetic interference of the power supply itself, and it also meets the requirements of the promised indicators, it is inevitable that the electromagnetic interference of the power supply will exceed the standard in market applications; at this time, many design engineers will think that the root of the problem is The power supply is actually misunderstood, because the electromagnetic interference conduction disturbance test item is mainly aimed at the power port, so the power port becomes its transmission path, and all electromagnetic interference will pass through the power port to reach the power port. However, in addition to the power supply itself, the electromagnetic interference tested by the test equipment mainly includes the electromagnetic interference generated by other parts of the whole machine, as well as the electromagnetic interference generated by the resonance of the internal parasitic parameters of the equipment. This type of electromagnetic interference It will be coupled to the test equipment through the power port. The filter inside the power supply cannot filter this part of the electromagnetic interference. The application environment of the power supply varies greatly. All power supply design filter parts are based on solving their own interference. At the same time , the filter attenuation characteristics and spectrum characteristics will try to reserve the largest margin, but it is impossible to be compatible with all applications; then this requires our complete machine designers to follow the application circuit recommended by the power supply manufacturer when designing the front end of the power supply design.
2 Electromagnetic immunity:
In addition to meeting the electromagnetic interference requirements mentioned above, the power supply must also meet the immunity requirements of the corresponding application environment. If the minimum requirements of this environment cannot be met, it will be affected by the electromagnetic interference generated by other surrounding equipment, causing damage, Abnormal phenomena such as unstable output will eventually affect the normal operation of the whole machine.
For general-purpose products such as power supplies, there is no specific standard that requires the immunity performance to reach a certain level. When it is applied to a specific industry, refer to the industry standard; The specific requirements of the general standard IEC/EN61000-6, the standard IEC/EN61000-6-1/2 is divided into the immunity requirements of industrial environment equipment and the immunity requirements of residential areas, commercial areas and light industrial environments. The AC-DC part of MORNSUN power supply is designed according to the strictest level of industrial products, and at the same time, it ensures that the design margin is very sufficient. At present, this type of power supply promises four-level indicators of 2KV (differential mode) / 4KV (common mode) For products with protection capabilities, the internally designed port protection piezoresistors all use 14D specifications
It can be clearly seen from the table below that the continuous flow rate of 14D specifications can reach 4.5KA, so the promised index is only 1KA (differential mode)/333KA (common mode). From this comparison, it can be seen that the derating of the design is already very large. However, during the long-term use of the product in the market, the varistor will be damaged, which will eventually cause the power supply to burn out. The reason is mainly due to two factors: one is due to the aging of the varistor itself. The very commonly used ZnO varistor above has an insulating layer made of ZnO particles in the middle, and electrodes are formed by silver plating on both sides. When the voltage of the electrodes on both sides exceeds its threshold voltage, the leakage current will increase sharply, eventually forming a transient current. Release and play a protective role.
