Today we’re announcing the next generation of our Power over Ethernet (PoE) HAT. Compared to its predecessor, the Raspberry Pi PoE+ HAT delivers more power, implementing the 802.3at PoE+ standard; and it runs cooler, thanks to various design improvements. Best of all, we’ve been able to keep the original affordable price of $20.
The current global semiconductor shortage — which you’ll almost certainly have read about by now — is constraining our supply of the original PoE HAT. In general, we’re weathering the shortage very well, and the supply of mainline Raspberry Pi computers, Zeros and our other products have not been affected (we’re very good at pipelining). Unfortunately, the first-gen PoE HAT uses silicon that’s in short supply.
The old HAT will remain in production, but we are taking the unusual step of announcing this new product before we have stock in channel, so that industrial customers can consider migrating to the new PoE+ HAT, which will have shorter lead times. The Raspberry Pi PoE+ HAT will be available from our Approved Resellers in early June. (Visit our Products page to be automatically directed to your local Approved Reseller when you select a product.)
Power (over Ethernet) to the people
One of the coolest features we’ve added to Raspberry Pi in the last few years has been Power over Ethernet (PoE) support. From Raspberry Pi 3B+ onward, we use an Ethernet jack with the appropriate taps on its windings, and connect those taps to an additional 4-pin header, located just beneath the top-right mounting hole. A HAT can pick up these signals, request power from the switch, and regulate the resulting 37-57V DC down to 5V to power the Raspberry Pi.
At the end of 2018, we released the Raspberry Pi PoE HAT, which did just this. After some embarrassing teething troubles, it has become one of our best-selling accessories. We’ve seen it used in industrial applications like digital signage and factory automation, and by hobbyists who want to put their Raspberry Pi somewhere remote, sharing a single cable for both power and data.
The original PoE HAT implements the 802.3af standard, and can deliver a guaranteed minimum of 13W to the Raspberry Pi. This is enough to power a Raspberry Pi 4 at maximum load, but not quite enough to power the hungriest USB peripherals at the same time.
The PoE+ HAT implements the 802.3at standard. When used with a compatible switch or injector this means it can deliver up to 25W, as you can see from this comparison table.
|PoE HAT||PoE+ HAT|
|Standards supported||802.3af||802.3af, 802.3at|
|Maximum output current||2.5A||5A|
|PCB||4 layers, 2oz copper||4 layers, 2oz copper|
|Compatible with||Raspberry Pi 3B+, 4B||Raspberry Pi 3B+, 4B|
A better diode rectifier
What else has changed? To reduce heat dissipation we replaced the diode rectifier with an “ideal diode” rectifier, in the form of a Microchip PD70224ILQ device.
A shiny new transformer
PoE implementations require a transformer to provide voltage conversion and isolation. When you think of a transformer, you probably think of wire wrapped around a ferrite core, and this is exactly what the original PoE HAT uses. For the PoE+ HAT, our friends at Bourns have provided us with a shiny new toy: a planar transformer.
As you can see from this disassembled version, in a planar transformer the “windings” are actually traces on a multi-layer PCB; the ferrite is assembled around the PCB. The result is a slimmer transformer (useful if you really care about z-height and are prepared to dispense with the fan) which is more suitable for surface-mount assembly. And it has the added benefit of looking like an artefact from the future.
We think you’ll notice a real improvement over the original and much-loved PoE HAT. We’re always fascinated to learn what work users end up putting their Raspberry Pis and accessories to — if you’re doing something particularly cool with PoE, let us know!