Reasons for Designing a POE (Power over Ethernet) Network Transformer Center Tap with Power Supply

Reasons for Designing a POE (Power over Ethernet) Network Transformer Center Tap with Power Supply

The POE (Power over Ethernet) Network Transformer Center Tap with Power Supply is primarily designed to enable the simultaneous transmission of data and power over Ethernet cables.  

For POE network transformers, the center tap (i.e. the 1-pin position you mentioned) is used for the power connection for the following main reasons

Bias voltage: The center tap provides a reference point or ground plane to which DC voltage can be added. This is necessary because the Ethernet signals are AC coupled and the POE power supply requires DC. By adding power to the center tap, it is possible to provide the required DC power to the device without interfering with data communications.

Isolation and protection: The transformer itself provides electrical isolation, which is important to prevent damage from potential differences between different devices. The power supply at the center tap is designed with this in mind to ensure safety and reliability.

Compatibility: The POE standard supports two types of power injection - one via data pairs (known as Mode A) and the other via free pairs (known as Mode B). Using a transformer with a center tap makes it easier for manufacturers to design products that are compatible with both modes.

Simplified circuit design: By using a center tap to bring in power, the design of a circuit board can be simplified, reducing the number of additional components, which lowers costs and improves efficiency.

Current balancing: When power is transmitted through pairs of wires, center taps help maintain current balance between the pairs, which is important for maintaining signal integrity and minimizing electromagnetic interference (EMI).