Functions of Network Transformer

In an Ethernet device, a network transformer is added in the middle when the PHY is connected to RJ45. Some transformer centers are routed to the ground. In addition, when the power supply is connected, the power supply value can be different, 3.3 V, 2.5 V, 1.8v all have.

The role of this transformer is analyzed as follows:

1. Why is there some power supply in the middle head? Some grounding? This is mainly determined by the use of the PHY chip UTP port drive type, which has two types, voltage drive and current drive. The voltage drive is connected to the power supply; the current drive is directly connected to a capacitor to the ground! Therefore, for different chips, the central tap method is closely related to the phy. For more information, see the datasheet and reference design of the chip.

2. Why are different voltages connected to the power supply? This is also determined by the UTP port level specified in the PHY chip information used. The corresponding voltage is required. That is, if it is 2.5 V, it will be pulled up to 3.3 V, if it is 3.3v, it will be pulled up to v.

3. What is the role of this transformer? Can it be left alone. Theoretically, transformer can be directly connected to RJ45 without being connected. However, the transmission distance is very limited, and when connected to different levels of Network Ports, it will also affect. In addition, the external interference to the chip is also great. After a network transformer is connected, it is mainly used for signal level coupling. First, the signal can be enhanced to make the transmission distance farther. Second, the chip end is isolated from the external end, and the anti-interference capability is greatly enhanced, in addition, the chip is greatly protected (such as lightning strikes). Third, when connected to different levels (for example, some PHY chips are 2.5 V, and some PHY chips are 3.3 V) does not affect each other's devices.