The principle of surge protection for switching power supplies
Surge Protective Device (SPD), also known as surge protector, is a nonlinear protective device used in live systems to limit transient overvoltage and guide discharge surge currents. It is used to protect electrical or electronic systems with low voltage resistance from lightning strikes, electromagnetic pulses from lightning strikes, or damage from operating overvoltage. In recent years, electronic information systems (such as television, telephone, communication, computer networks, etc.) have developed rapidly, and a large number of electronic information devices have emerged and become popular. These types of systems and equipment are often expensive and important, with low operating voltage and withstand voltage levels, and are highly susceptible to the hazards of lightning electromagnetic pulses. Therefore, SPD is needed for overvoltage protection.
Due to the different standards followed by different countries, there is no unified product specification, and the identification of parameters also has their own emphasis, which is far inferior to other electrical product specifications, which brings great inconvenience to design and selection. In engineering design, common brands can be divided into domestic products, European products, and American products based on their place of origin. Domestic products have chaotic parameter settings, diverse specifications, and high residual pressure. Standardized product model settings include some imitating European products, while others follow national standard parameters. Most products are labeled with In and Imax. Due to the low requirements of domestic products for application areas, low building grades, and high equipment voltage resistance, some parameter requirements can be appropriately relaxed.
European products are generally labeled with the maximum discharge current, and the product model is also set based on this parameter. For example, a well-known European brand XXX65 and XXX40, where the values of 65 and 40 are Imax. However, the standard in our country clearly stipulates that the nominal discharge current In should be used for selection, which is currently an awkward situation encountered in engineering design. After checking the product information, the In value of XX65 does not exceed 20kA, and the In value of XX40 does not exceed 15kA. If the recommended values of GB50343 are followed, these two products can only be used for three-level protection at the end of the equipment. However, in actual design, they are installed on the first and second levels, which is clearly inconsistent with the selection parameters of the national standard, and the residual voltage is relatively high. Ordinary models generally exceed 1200V. Once the wiring environment is not good, it is easy to exceed the equipment's withstand voltage value. Generally, European products have a smaller Uc value and are opportunistic in labeling line voltage, making it easier to mislead when selecting.
