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Popular Science 丨 Poe those things part Two: Standard Poe power supply process and how to identify non-standard Poe products
Nov 22, 2017

Part of the network or security engineering people in the choice of PoE switches, often feel a little puzzled, do not know how to choose, because the market in addition to 48V-powered products, often will find 24V or even 12V powered products, then what is the difference between these types? 48V power supply must be a standard PoE? This article discusses the power issues for standard and non-standard PoE devices in detail.

Standard and non-standard POE product definitions

First let's define standard and non-standard PoE products.

It goes without saying that the standard PoE product is in line with IEEE802.3af and IEEE802.3at protocol products, supply voltage standard value of 48V.

Non-standard PoE products refer to those products that directly supply DC power only by using the idle core of the network cable as the power supply wire, without the IC monitoring and management unit, and without detecting and judging PDs (powered devices). The provided DC power is usually 12V, 24V and 48V. Especially 48V non-standard products, often make people mistaken for the standard PoE.

Standard PoE product power supply standard

The standard PoE power supply mode requires that the PSE must have terminal detection, device classification, and power loss evaluation function, and the powered device (PD) should also be compatible with the IEEE802.3af protocol standard to be detected by the PSE. A true PoE solution is the only solution that meets both the PSE and PD requirements.


The standard PoE outputs three supply voltages throughout the power supply:

1, in the detection of whether the electrical equipment is legal (that is, Poe compatibility), the supply voltage is 2.5v~10v;

2, detection, if the electrical equipment (PD) is valid, then the PD classification (according to the PD power divided into 5 power supply), in the grading phase PSE power supply voltage is 15-20v;

3, grading finished, stable power supply, stable in 48V.