Power consumption is on everyone’s specification checklist these days. Minimal power consumption means longer use between charges for smart phones, tablets, and laptops. It also means not having to liquid-cool thousands of cores in high-performance computing (HPC) systems. And, it means that devices can be wired and powered using different technologies like Power-over-Ethernet (PoE).
PoE has been around for more than a decade. It’s well known in the network industry, but it has been primarily used for network devices like wireless access points and Voice over Internet Protocol (VoIP) telephones. It greatly simplifies wiring since deployment no longer requires a power outlet.
PoE requires a 48-V source that’s typically found in the Ethernet hub or switch. It’s possible to add a power injector inline with a connection, but that tends to be used as a stopgap measure or when only a single PoE device is needed.
Managing PoE
I’ve been working with Super Micro Computer’s (aka Supermicro) SSE-G2252P Gigabit Ethernet (Fig. 1) intelligent non-blocking layer 2 switch (see “Ethernet Switch Manages Power Over Ethernet Resources” at electronicdesign.com). It’s a managed switch, and the PoE support is more extensive than most.
Figure 1. Super Micro Computer’s SSE-G2252P layer 2, non-blocking Gigabit Ethernet switch provides more extensive managed PoE support than most other alternatives.
PoE started by delivering 15.4 W (the minimum is 44 V dc at 350 mA), but the standard has since been extended to deliver more power. The PoE Plus (PoE+) standard kicks up the limit to 25.5 W. The SSE-G2252P lets network managers specify the maximum amount of power per port. The switch has a maximum budget of 400 W.
I like the additional management that Supermicro put into the device. It supports scheduling and power distribution priority, which means my access points remain up even when I try to plug in too many PoE devices in the lab. It also has overload protection.
Delivering POE Solutions
One of those devices in the lab is using the WinSystems PPM-PS394 (Fig. 2) to power a PC/104 Plus stack. The board fits into the stack and takes power from a pass-through PoE connection or dc source from 9 to 32 V. It can deliver up to 10 A at 5 V and 5 A at 3.3 V to the rest of the stack or other devices connected to it.
Figure 2. The WinSystems PPM-PS394 PoE node can power a PC/104-Plus stack.
The rats nest in the photo is connected to the WinSystems PCM-VDX-2 PC/104 board hidden under the PPM-PS394. It runs a 1-GHz Vortex86DX processor, which is a 32-bit x86 system-on-chip (SoC) designed for low-power applications that easily runs on the minimum PoE setting.
The board has a pair of Ethernet ports. One will typically be connected to the PPM-PS394 pass-through. It also has the usual complement of serial I/O, parallel I/O, and four USB 2.0 ports. It’s designed for headless operation, although it can accept the optional Volari XGI MiniPCI card with a VGA output.
I used the full peripheral complement, including booting from a Compact Flash card, and ran Linux. It also supports DOS and x86 real-time operating systems (RTOS) or most other 32-bit x86 operating systems. The package uses about 7 W or half the base PoE budget. That means a PC/104 stack can be built up without busting the PoE switch. The system was plug-and-play all the way. Of course, the rats nest on the lab bench goes away once the hardware is placed inside a system for a target application.
The PoE board cannot drive all combinations of PC/104 hardware, but it can handle quite a few. Even the newer PXM-C388-S board with a 1.66-GHz Atom processor, on-board video, and SATA support only needs about 10 W. There are some PoE switches for the home market, but this approach is more likely to find a home on the shop floor or in other industrial application areas where embedded devices are quite common. Best of all, PoE doesn’t require a software change.