Transformer Introduction
The products are mainly used in: high-performance digital switches; SDH/ATM transmission equipment; ISDN, ADSL, VDSL, POE power receiving equipment integrated service digital equipment; FILT optical fiber loop equipment; Ethernet switches, such as the YL18-2050S and YL18-3002S of Yutai Electronics, are common! The data pump is a device on the consumer PCI network card. The data pump is also called a network transformer or a network isolation transformer. It plays two main roles on a network card. One is to transmit data. It filters the differential signal sent by PHY with differential mode coupled coil coupling to enhance the signal, and through electromagnetic field conversion, it is coupled to the other end of the connecting network cable at different levels; The first is to isolate the different levels between different network devices connected by the network cables, so as to prevent different voltages from damaging the devices when they are transmitted through the network cables. In addition, data mercury can also play a certain role in lightning protection of equipment.
Transformer function
In Ethernet equipment, when connecting RJ45 through PHY, a network transformer will be added in the middle. Some transformer center taps are grounded. When connecting to the power supply, the power supply value can be different, including 3.3V, 2.5V and 1.8V. The function of this transformer is analyzed as follows:
1. Why are some of the intermediate taps connected to the power supply? Some grounding? This is mainly determined by the type of PHY chip UTP port drive used. There are two types of drive, voltage drive and current drive. For current drive, the tap shall be connected to the power supply; Voltage driven devices are grounded through capacitors. Therefore, for different chips, the connection of the center tap is closely related to PHY. For details, please refer to the datasheet and reference design of the chip.
2. Why do you connect the power supply with different voltages? This is also determined by the UTP port level specified in the PHY chip data used. The determined level must be connected to the corresponding voltage. That is, if it is 2.5v, it will be pulled up to 2.5v; if it is 3.3v, it will be pulled up to 3.3v.
3. What's the function of this transformer? Can it be disconnected. Theoretically, it can be directly connected to RJ45 without connecting transformer, and it can work normally. However, the transmission distance is very limited, and when connected to different level network ports, it will also have an impact. And the external interference to the chip is also great. When the network transformer is connected, it is mainly used for signal level coupling. First, the signal can be enhanced to make its transmission distance longer; Secondly, the chip end is isolated from the outside, the anti-interference ability is greatly enhanced, and the chip is greatly protected (such as lightning strike); Third, when connected to network ports of different levels (for example, some PHY chips are 2.5V, and some PHY chips are 3.3V), they 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). When the PHY output signal is sent to a place 100 meters or more, there will be a great loss of DC component. Moreover, if the external network cable is directly connected to the chip, electromagnetic induction (thunder) and static electricity can easily cause damage to the chip.
In addition, different grounding methods of equipment and different grid environments will lead to inconsistent 0V levels of both parties. In this way, the signal will be transmitted from A to B. Because the 0V level of equipment A is different from that of point B, it may cause a large current to flow from equipment with high potential to equipment with low potential.
The network transformer filters the differential signal sent by PHY with differential mode coupled coil coupling to enhance the signal, and couples it to the other end of the connecting network cable through the conversion of electromagnetic field. This not only makes the network cable and PHY have no physical connection, but also transmits the signal, blocks the DC component in the signal, and can also transmit data in devices with different 0V levels.
The network transformer itself is designed to withstand the voltage of 2KV~3KV. It also plays a lightning protection role. Some friends' network equipment is easy to be burnt out in thunderstorm weather. Most of them are caused by unreasonable PCB design, and most of them burn out the interface of the equipment. Few chips are burnt out, but the transformer plays a protective role.
The isolation transformer can meet the insulation requirements of IEEE802.3, but cannot suppress EMI.
