Power Over Ethernet PoE Switch Application

With the rapid development of technologies such as the Internet of Things, big data, 5G and artificial intelligence, industrial automation and industrial Internet of Things have become a development trend. The demand for industrial Ethernet switches is rapidly expanding, and the demand is growing rapidly, especially in manufacturing execution systems. It is widely used in industrial automation application scenarios such as (MES), production scheduling system (PLC) and process control system (FCS).

In most cases, the terminal equipment needs DC power supply, and the terminal equipment is usually installed on the ceiling or outdoors relatively high from the ground, and it is difficult to have a suitable power socket nearby. Even if there is a socket, it is difficult to find a place for the AC-DC converter required by the terminal equipment Therefore, the requirement to provide power support through Ethernet itself is becoming more and more urgent, and Power over Ethernet PoE just solves this problem.

Figure 1: Common PoE power supply applications

PoE is a wired Ethernet power supply technology. The network cable used for data transmission also has the capability of DC power supply. PoE power supply has the advantages of reliability, simple connection, and unified standards. As shown in Figure 1, more and more industrial IoT devices are powered by PoE, such as IP phones, network video surveillance, and wireless Ethernet devices.

A PoE switch is a common device used to provide PoE power. It is generally called a PSE (Power-sourcing Equipment), and a PSE controller chip is used inside. According to the three PoE standards issued by the IEEE Standards Committee, the power supply voltage range is DC 44V~57V, usually 48V or 53V, and usually powered by an AC to DC adapter. Common PoE switch adapters are divided into three types:

Using a 12V adapter for power supply, the 12V voltage needs to be raised to 48V/53V to power the input of the PSE chip.

Using a 48V/53V adapter for power supply can directly provide 48V/53V power for the PSE chip, but a step-down IC is required to reduce the 48V/53V to 12V, 5V, 3.3V and other voltages. For high-power scenarios, the voltage is usually lowered to 12V first; then the secondary power supply medium-voltage high-current or low-current step-down converter is used to reduce the voltage to 5V, 3.3V, etc.

The 48V/53V adapter is used as the input power supply of the PSE chip, and the 12V adapter will use a medium-low voltage high-current or low-current step-down converter to drop to 5V, 3.3V and other voltages.

In addition to the adapter, in the power architecture of the POE switch, some PSE chips have integrated LDOs inside, which can directly support 48V/53V as the working voltage, and some need to use a step-down IC to drop the power supply to 3.3V; at the same time, the output of the POE switch The number of ports increases from few to many, the transmission speed ranges from 100M to 1000M, the output power increases from small to large, and the required power supply current gradually increases. Usually, a step-down IC with high current is used.