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Common mode inductor core design factors

2019-04-03 10:09:54

On some motherboards, we can see the common mode inductor core, but on most motherboards, we will find that the component is omitted, and even some locations are not reserved. Is such a motherboard qualified?
It is undeniable that the common mode inductor core has a good suppression effect on the common mode interference of the high-speed interface of the motherboard, and can effectively prevent the EMI from forming electromagnetic radiation through the cable to affect the normal operation of the remaining peripherals and our physical health. But it is also worth noting that the EMI design of the board is a fairly large and systematic project, and the design of the common mode inductor is only a small part of it. The high-speed interface has a common-mode inductor design board, and it is not good to have an overall anti-EMI design. Therefore, from the common mode filter circuit we can only see one aspect of the board design, which is easily overlooked by everyone, and it is a mistake to see the wood.
Only by understanding the overall anti-EMI design of the board can we evaluate the advantages and disadvantages of the board. So, what do the excellent board design generally do in terms of EMI prevention?
1. Motherboard Layout design
2. Cutting off the motherboard wiring
3. The design of the motherboard interface

I don't know if you noticed that the motherboard will be accompanied by an open thin iron strip. In fact, this is also used to prevent EMI. Although the EMI shielding performance of the chassis is good, the electromagnetic wave will leak from the opening of the chassis surface, such as the PS/2 interface, the USB interface, and the opening of the serial port. The size of the hole determines the degree of leakage of electromagnetic interference. The smaller the aperture of the opening, the greater the degree of attenuation of the electromagnetic interference radiation. For a square hole, L is the diagonal length.
After the blank is used, the metal contacts on the blank and the input and output parts of the motherboard are well grounded through the chassis, which not only attenuates the EMI, but also reduces the size of the square hole and further reduces the L value. More effectively shield electromagnetic interference radiation.
The above three points are just a few of the main anti-EMI designs in the motherboard design except for the circuit design. It can be seen that the anti-EMI design of the motherboard is a whole concept. If the overall design is unqualified, it will bring a large electromagnetic Radiation, and these are not compensated by a small common-mode inductor core.