PoE Powered Device Design: Drawing Power from the LAN with WIZPoE-P1
Understand the IEEE 802.3af/at PoE standard and use the WIZPoE-P1 module to design a powered device (PD) that draws power from the Ethernet cable — no separate power wiring.
Published: 2025-03-05
PoE basics: 802.3af / at
Power over Ethernet carries data and power on the same RJ45 cable. The supplying side is the PSE (e.g. a PoE switch); the receiving side is the PD (your device).
The standard sequence is: the PSE first detects the PD's signature resistance at low voltage, then performs power classification, and only after that applies roughly 44–57V DC. 802.3af delivers about 13W and 802.3at (PoE+) about 25W.
The WIZPoE-P1 module
The WIZPoE-P1 is an 802.3af/at-compliant PD module that handles detection, classification, and the isolated DC/DC conversion internally. It accepts a 36–57V PoE input and outputs a regulated 5V at up to 8W, with efficiency above 85%.
For the designer it packages the trickiest part of PoE into a single module: you simply feed the PoE supply in and take the 5V output to your own circuit.
Application circuit & power budget
A typical topology is: the RJ45 (with center-tapped magnetics) extracts the PoE power → into the WIZPoE-P1 → the module's 5V output feeds the downstream circuit (e.g. a W5500-based IP camera or sensor).
Always estimate the whole-unit power budget first and confirm it stays within the supply ceiling of your chosen PoE class, leaving headroom on the 5V rail. If the unit approaches the 8W ceiling, review the thermal design and input current.
Products mentioned
WIZPoE-P1 PoE Powered Device Module (8W)
WIZPoE-P1 is a WIZnet IEEE 802.3af/at standard PoE Powered Device (PD) module that draws power directly from the Ethernet cable, outputting 5V at up to 8W — no separate power cable needed. Suitable for IP cameras, industrial sensors, APs, access control devices, and other PoE-powered applications.
W5500 Hardwired TCP/IP Ethernet Controller
W5500 is WIZnet's flagship Ethernet controller with a unique hardwired TCP/IP stack, enabling direct network connectivity without software TCP/IP implementation. Connects to the host MCU via SPI, features 32KB TX/RX buffer, supports up to 8 sockets — the most widely adopted Ethernet chip in the Arduino/Raspberry Pi ecosystem.
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