What is a network transformer？

Transformer function: In Ethernet equipment, when connecting RJ45 through PHY, a network transformer will be added in the middle. Some transformers have their center tap connected to ground. And when the power supply is connected, the power supply value can be different, 3.3V, 2.5V, and 1.8V are available. The role of this transformer is analyzed as follows:

    1. Why are some of the middle taps connected to the power supply? Some ground? This is mainly determined by the driving type of the UTP port of the PHY chip used. There are two types of driving, voltage driving and current driving. For current-driven, the tap needs to be connected to the power supply; for voltage-driven, it is grounded through a capacitor. Therefore, for different chips, the connection method of the center tap is closely related to the PHY. For details, please refer to the datasheet and reference design of the chip.

transformer

    2. Why do you connect different voltages when connecting to the power supply? This is also determined by the UTP port level specified in the PHY chip data used. What level is decided, you have to connect the corresponding voltage. That is, if it is 2.5v, it will be pulled up to 2.5v, and if it is 3.3v, it will be pulled up to 3.3v.

    3. What is the function of this transformer, can it be left out? In theory, it is possible to connect it directly to the RJ45 without the need for a transformer, and it can work normally. However, the transmission distance is very limited, and when it is connected to a different level network port, it will also have an impact. And the external interference to the chip is also very large. When connected to the network transformer, it is mainly used for signal level coupling. First, it can enhance the signal and make the transmission distance longer; second, the chip end is isolated from the outside, the anti-interference ability is greatly enhanced, and a great protection effect (such as lightning strike) is added to the chip; When it reaches the network ports of different levels (for example, some PHY chips are 2.5V, and some PHY chips are 3.3V), it will not affect each other‘s devices.

Transformer function

1. Electrical isolation

   The signal level generated by any CMOS process chip is always greater than 0V (depending on the process and design requirements of the chip), and the PHY output signal will have a large loss of DC components when it is sent to a place of 100 meters or even longer. . And if the external network cable is directly connected to the chip, electromagnetic induction (lightning) and static electricity can easily cause damage to the chip.

    Then there are different grounding methods of equipment and different power grid environments, which will cause the 0V level of both sides to be inconsistent, so that the signal is transmitted from A to B. Since the 0V level of A device is different from the 0V level of point B, this may lead to a large amount of damage. Current flows from a device with a higher potential to a device with a lower potential.

The network transformer filters the differential signal sent from the PHY with the differential mode coupling coil coupling to enhance the signal, and is coupled to the other end of the connecting network cable through the conversion of the electromagnetic field. In this way, there is no physical connection between the network cable and the PHY, and the signal is transferred, and the DC component in the signal is cut off, but also data can be transmitted in devices with different 0V levels.

     The network transformer itself is designed to withstand the voltage of 2KV~3KV. It also plays a role in lightning protection. Some friends‘ network equipment is easy to be burnt out during thunderstorms. Most of them are caused by unreasonable PCB design, and most of them have burned the interface of the equipment. Few of the chips are burned, and the transformer has played a protective role.