Why does Ethernet interface require a network transformer? Why connect a network transformer?

       In modern wired network devices, whether it is home routers, switches, computer network cards, network cameras, or industrial gateways PLC、 As long as professional equipment such as fiber optic transceivers are equipped with RJ45 Ethernet interfaces, network transformers will definitely be installed in the circuit. Many hardware developers, circuit designers, and industry practitioners have questions: can Ethernet signals be directly transmitted through Ethernet cables connected to the main control chip and PHY chip? Why is there a unified requirement in the industry to install network transformers at the network port location? In fact, network transformers are not optional accessories, but essential core magnetic components in Ethernet communication systems. They play multiple key roles such as electrical safety protection, signal optimization, electromagnetic compatibility, and circuit protection, and are the foundation for ensuring network stability, equipment safety, and product compliance.

     When an Ethernet signal is input to the main coil, the current in the main coil will generate a magnetic field. The magnetic field will be transmitted to the secondary coil through magnetic coupling, thereby generating an induced current in the secondary coil. In this way, the Ethernet signal is transmitted from the main coil to the secondary coil.

Through network transformers, the following functions can be achieved:
1. Signal isolation: Network transformers can isolate Ethernet signals between the main and secondary coils to prevent interference between signals in different circuits. This is very important for improving signal quality and reducing noise, especially in long-distance transmission and poor noise environments.
2. Signal matching: Ethernet interfaces typically use different electrical signal levels and impedances. A network transformer can convert the electrical signals between the main coil and the secondary coil to match them with each other. This can ensure the transmission quality and reliability of the signal.
3. Filtering and Suppression: Network transformers can improve the anti-interference ability of Ethernet signals by filtering and suppressing electromagnetic interference. It can filter out high-frequency and low-frequency interference, and perform distortion correction on signals, thereby improving the accuracy and stability of data.
4. Adjust voltage: The network transformer can also adjust the voltage level of the signal to meet the requirements of the receiver. This is crucial for ensuring the normal transmission of data between different devices, especially in the case of multi device networking and cross network transmission.

So, why does an Ethernet interface require a network transformer? There are several main reasons for this:

1. Electrical isolation and high voltage protection: They are the most essential and irreplaceable functions of network transformers, and the primary reason why network port circuits must be installed with them. Ethernet relies on twisted pair cables for long-distance wiring, and network cables shuttle through complex environments such as indoors, corridors, and outdoors, making them highly susceptible to high-voltage impacts such as lightning induced voltage, power grid surges, human static electricity, and line leakage. Ordinary network cables are exposed lines without any insulation protection capability. Once the instantaneous high voltage of thousands of volts is directly connected to the interior of the equipment, it will instantly penetrate the precision Ethernet PHY chip and main control circuit, causing permanent damage to the equipment. The network transformer uses the principle of electromagnetic induction to transmit signals, and there is no electrical direct connection between its primary winding (connected to the internal PHY chip of the device) and secondary winding (connected to the external RJ45 network cable). It relies on magnetic energy to transmit signals through the air, forming a sturdy electrical isolation barrier.

The insulation withstand voltage of conventional network transformers can reach over 1500V AC, and the withstand voltage of industrial grade products can even reach 3000V AC, effectively blocking the intrusion of high voltage generated by lightning strikes, surges, and static electricity into the equipment. In addition, there is a common ground potential difference between different network terminal devices. Computers, switches, security cameras, and industrial equipment are connected to different power supply circuits, and the reference ground potential of each device cannot be completely consistent. If the PHY chip is directly connected to the network cable, the ground potential difference will form a continuous DC circulating current, which will not only interfere with data signals, cause network packet loss, delay, and communication interruption, but also erode the chip circuit for a long time, shortening the service life of the equipment. The isolation structure of the network transformer completely cuts off the ground loop current, allowing the internal circuit of the equipment to be independent of the external network cable, solving a series of problems caused by ground potential difference from the root, and also improving the personal safety of equipment use, meeting the basic requirements of electrical safety regulations.

2. Fault protection: Network transformers can also provide certain protection mechanisms. When the Ethernet interface fails, it can prevent the fault signal from being transmitted to the host and other devices through isolation and disconnection.

3. Signal matching: Due to the use of different electrical signal levels and impedances in Ethernet interfaces, network transformers can convert input signals into signals suitable for receivers. This can ensure accurate transmission and reception of signals.

4. Interference suppression: Network transformers can suppress electromagnetic interference and circuit noise, improving the anti-interference ability of Ethernet signals. This is crucial for ensuring the accuracy and stability of data, especially in complex network environments.

5. Adapt to Ethernet POE power supply system to achieve co line transmission of network cable data and power. Nowadays, devices such as network cameras, wireless APs, and IoT terminals widely use POE power supply technology, which uses the same twisted pair cable to simultaneously transmit network data and 48V DC power supply, simplifying the wiring process. The center tap design of network transformers can separate AC data signals from DC supply voltage, allowing power and data to work in parallel on the same line without affecting each other. If the network transformer is removed, the POE power supply architecture will not be able to be implemented, which will greatly limit the application scenarios of the device.

In addition, from the perspective of circuit design and manufacturing, integrated network transformers can also simplify hardware design and reduce overall costs. In early circuit designs, engineers needed to separately pair multiple discrete components such as pulse transformers, common mode inductors, and isolation devices to achieve equivalent functionality. This not only resulted in complex PCB wiring and occupied a large amount of board space, but also increased costs for material procurement, surface mount processing, and quality control. The integrated network transformer integrates functions such as isolation, transformation, and filtering, and a single device can meet all needs, effectively simplifying the circuit structure and improving the consistency of product mass production.

In summary, network transformers are important components of Ethernet interfaces, capable of isolating and converting electrical signals, providing signal matching and interference suppression functions. It plays a crucial role in protecting interfaces and devices from interference and damage, while also improving the quality and reliability of data transmission. Omitting the network transformer not only leads to problems such as shorter transmission distance, signal distortion, and unstable network, but also causes the equipment to lose its high-voltage protection capability, making it prone to chip burnout and unable to pass industry certifications such as safety regulations and electromagnetic compatibility. Therefore, network transformers have become a standard component for all Ethernet interfaces and an indispensable part of wired network communication.