Introduction of a Simple Network Port Protection Scheme for Industrial Switch

According to the relevant provisions of IEC 1312-1 protection against lightning electromagnetic pulse, the building is divided into four areas: lpzoa area. All objects in this area may be directly struck by lightning, and the electromagnetic field in the area is not attenuated; In lpzob area, it is impossible for objects in this area to be directly struck by lightning, and the electromagnetic field in the area is not attenuated; In lpz1 area, objects in this area cannot be directly struck by lightning, and the electromagnetic field in the area may be attenuated; Lpz2 area is the subsequent lightning protection area. According to the above zoning principles, the industrial switch shall be placed in lpz2 area as far as possible to reduce the impact of lightning electromagnetic pulse on the industrial switch.

The following schemes can be designed for both 100m and Gigabit networks.

2、 Board level requirements for switch lightning protection

The surge capacity of the Ethernet port protection scheme: dm2kvcm6kvperituk.2110/700 μ s40Ω。

Due to the large number of industrial switch interfaces and limited space, multi-channel integrated network interface transformer and PHY are mostly selected, but the simplest protection scheme is also being selected at present. The above figure is the simple protection scheme used in the current application. The protection scheme is divided into common mode protection and differential mode protection. Generally, two leiditechp3100sc TSS and four lc3311ccw are selected as differential mode protection for Gigabit network. Note that TSS generally needs to be connected in parallel with high-voltage capacitor and resistance.

In particular, the device chip is patented, which can meet the requirements of high temperature and long-distance test without packet loss. If the space needs to be saved, a two-in-one TSS discharge tube, p3100sc-2, with the same volume, is used to ensure two channels.

3、 Grounding system of industrial grade switch

The grounding of industrial switch includes: DC power grounding; Shielding grounding of telecommunication equipment casing or frame; Metal sheath or shielding grounding of inbound communication cable; Grounding of incoming lightning arrester of open line or cable and grounding of empty line pair of signal cable, etc. In order to do a good job in the grounding of industrial switches, some units separately make a pair of artificial grounding electrodes for industrial switches, and the grounding resistance of the grounding electrodes also meets the requirements of the specifications. However, due to the limitation of the site, the distance between the artificial grounding electrodes and the lightning protection grounding of the building is less than 20m. In order to solve the above problems, the common practice is to connect all the grounding of the industrial switch with the communication grounding device shared by the whole station, and then connect the common grounding device with the lightning protection grounding of the building to form a joint grounding electrode. After the joint grounding electrode is adopted, the grounding device of communication equipment shall adopt a special grounding trunk line, and the cross-sectional area of the trunk line shall not be less than 25mm2.

4、 Conclusion

Overvoltage protection devices are required for interface protection of electronic products. Many engineers realize that protection devices should be used. However, due to improper selection or failure to follow the design principle of ESD circuit PCB, the product fails the electrostatic test or EMC test. The product has been verified and tested for many times, wasting human and financial resources, resulting in delayed listing of products, or over design, resulting in cost pressure.

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