Four Wire Pair PoE Detection Circuit
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Solution Overview
Problem
Conventional Power Over Ethernet (PoE) systems require two separate Power Sourcing Equipment (PSE) systems to supply power to devices using all four wire pairs, increasing cost and size, especially for high power applications.
Innovation Solution
A single PSE system supplies power to a Powered Device (PD) using all four twisted wire pairs in a CAT-5 Ethernet cable, with two pairs providing positive voltage and the remaining two pairs connected to low voltage, utilizing resistors and a MOSFET to detect and manage current for efficient power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two separate PSE systems are used to supply power over all four wire pairs, then high power delivery is achieved, but system cost and size increase
Solution Approach 1:
The patent combines two separate PSE systems into a single integrated PSE that can supply power over all four wire pairs. The single PSE includes a controller that manages power delivery across pairs 18, 20, 21, and 22, eliminating the need for two independent PSE systems while maintaining high power delivery capability. This merging reduces system cost, size, and complexity.
Solution Approach 2:
The single PSE system is designed to perform multiple functions: it can supply power over two wire pairs when a PD is PoE-enabled, and it can supply power over all four wire pairs when a PD is PoE-plus enabled. The controller adapts its operation based on the PD's capabilities, making the PSE universal and eliminating the need for separate dedicated systems for different power levels.
2Device complexity
If a single PSE system supplies power over all four wire pairs, then cost and size are reduced, but detection of PoE-plus capability becomes more complex
Solution Approach 1:
The controller performs preliminary detection by applying a first current limited voltage to pairs 18 and 20, then a second current limited voltage, and detecting the resulting current to determine if the PD is PoE-enabled. Based on this preliminary detection, the controller then applies a third current limited voltage to pairs 21 and 22 and detects the resulting current to determine PoE-plus capability. This staged preliminary action simplifies the overall detection process.
Solution Approach 2:
The detection process uses feedback from current measurements at different voltage levels to determine PD capability. The controller detects current resulting from applied voltages and uses this feedback information to determine whether the PD is PoE-enabled or PoE-plus enabled, and to control subsequent power delivery accordingly.
Data Source
AI summary
In a method performed by a PoE system, a PSE is able to detect whether a PD is compatible for receiving power via four wire pairs in the standard Ethernet cable. The PSE provides a current limited voltage to a first and second pair of wires in the cable, during a detection phase, to detect a characteristic impedance of the PD. In the PSE, a first resistor is connected to a third wire pair and a second resistor is connected to a fourth wire pair. During the detection phase, the PSE detects the relative currents through the resistors. If the currents are the same, then the PSE knows the PD is able to receive power via the four wire pairs. The PSE then applies the full PoE voltage to the first and second wire pairs and connects the third and fourth wire pairs to a low voltage via a MOSFET.