Introduction
There is a clear trend and market need for high-power transmission over cable. Power over HDBaseT (POH) enables
the transfer of DC power in conjunction with data signals over a single Ethernet cable to a distance of up to 100
meters (m). The POH standard is based on the IEEE 802.3at standard with the appropriate modifications to enable safe
delivery of up to 100 watts (W) over the four-pairs of the Ethernet cable. In this document we will review the evolution
of Power over Ethernet (PoE) from the days of IEEE 802.3af (delivery of 15.4W) to IEEE802.3at (delivery of 30W), up to
the HDBaseT power standard, POH, that specifies safe delivery of up to 100W. The POH standard includes definitions
of the power source equipment (PSE) and the powered device (PD), and this paper will describe the detection and
protection mechanisms that were set in the POH standard to ensure safe and reliable power is delivered to the
HDBaseT network. We will also review the benefits of using POH for the HDBaseT top target applications.
The Evolution of Power over Ethernet Standards
It is possible to trace the history of Power over Ethernet (PoE) to 1876, when Alexander Graham Bell invented the
phone. At the time, Bell had to decide whether the phone at each house would be powered locally, with a local battery,
or if the phone company would power the phones remotely. Bell chose to remote power phones, so there could be
central power backup in case of power outages (which were very common in those days). Fast forward to 1990,
10BaseT is ratified by IEEE802.3 with Ethernet running on a twisted pair. With the higher bandwidth and the switched
topologies that started to prevail, VoIP then became possible. Interestingly, the same issue of remote backup then
appeared again, creating the need to add power capabilities to Ethernet.
But PoE, unlike the original Bell telephony, came into a world where billions of non-PoE capable devices had
already been deployed. So, PoE was created with safety and interoperability in mind. IEEE802.3af-2003 was the
first version of PoE, which supported loads of up to 12.95W, such as IP phones, IEEE802.11g WLAN access points and
network cameras. As IEEE802.11n was about to become a reality, it was clear that more power was needed and the
IEEE802.3at-2009 standard was created, increasing power to 25.5W per device and cable. The POH standard is based
on the IEEE 802.3at standard with the appropriate modifications to enable safe delivery of up to 100W over the fourpairs of the Ethernet cable.
HDBaseT Technology and Power over HDBaseT
HDBaseT technology connects home entertainment systems and devices using a feature called 5Play™ that enables
up to 8 Gbps (the equivalent of 10.2 Gbps of HDMI) of uncompressed video and audio, 100BaseT Ethernet, control
signals and power to share the same cable, across distances up to 100m using standard RJ-45 connectors (see Fig. 1).
HDBaseT technology can support up to eight, 100m cable hops. HDBaseT also has the capacity to support double
the resolution of today’s video content, which is required for 3D integration and 2K and 4K formats. Unlike other
technologies that require a specific cable or a new, proprietary connector, HDBaseT uses the existing Cat5e/6
infrastructure.
HDBaseT’s powering capabilities are increasingly important as consumers bring more and more electronic devices
into the home. Using HDBaseT, a single LAN cable can provide up to 100W of power, over distances up to 100m,
requiring no additional power source. Allowing for the drop over 100m of cable, the power to the device is typically
75W. The technology has enough headroom to power the vast majority of these products. Today’s Energy Star™ 6.1
specifications restrict all TVs up to and including 60 inches to less than 100W. In fact, a typical 42-inch TV cannot
surpass 65.9W. These specifications are constantly evolving (for the latest specifications and revisions, see more at
https://www.energystar.gov/certified-products/detail/486/partners?fuseaction=products_for_partners.showTVs. At
these levels, HDBaseT has ample power delivery capabilities, even for supporting very large displays.
HDBaseT power capabilities also solve the problem manufacturers have faced with providing thinner, lighter wallmounted TVs that have been encumbered by complicated companion AC-to-DC and DC-to-DC power circuitry.
HDBaseT replaces this AC-to-DC circuitry with a single, convenient cable/connector so that, for instance, wall-hung
TVs connected via an HDBaseT-enabled Cat5e or better cable will require no other power source.
Additionally, HDBaseT’s power-delivery technology provides the foundation for new opportunities to manage overall
power consumption and efficiency. These capabilities are enabled by the underlying PoE technology that has become
a critical element of the latest POH specification.
More PoE Power, Better Efficiency
The original, low-power IEEE802.3af standard used two out of the four pairs of wires existing in a Cat5e cable, while
the more recent IEEE802.3at-2009, or “PoE+” specification, enables power to be delivered over all four pairs. These
latest PoE specifications also add mechanisms for device detection, classification, disconnection and protection
from overload/short conditions, while also adding many new advanced, “smart” energy-management capabilities.
In a typical POH implementation, the PSE is installed and powered by a 50- to 57-volt DC power supply, and all PDs
then receive power directly over the HDBaseT link across all four pairs of Cat5-or-better cables. Four-pair powering
is the key to delivering more power with greater efficiency. Defined in the latest high-power PoE standards, four-pair
powering gives PDs two power interfaces so they can receive twice the power of earlier two-pair solutions by using
all four pairs of Ethernet cable (see Fig. 2). Nothing precludes the two power interfaces to be connected−one over the
two pairs using lines 1, 2, 3 and 6, and the other using the two pairs that use lines 4, 5, 7 and 8. This is what makes it
possible to increase power delivery while fully complying with the standard.
Additionally, core PoE technology has been enhanced for the POH specification to include a higher current of almost
1 amp (A) for every two pairs, with an appropriate three-event classification that identifies POH PSEs. This enables
POH technology to transfer of up to 100W of continuous DC power, per port, from one side of the HDBaseT link to the
other. Unlike in PoE, where the PD must assume a worst-case cabling infrastructure at all times, POH enables the
PD to identify the cable length/resistance and draw more power, as long as the overall power consumption does not
exceed 100W. POH is fully backwards-compatible with the IEEE802.3at-2009 PoE specification, including the section
33.7.1 mandate that all power sourcing equipment (PSE) conform to IEC 60950-1:2001 and be classified as a Limited
Power Source (LPS) carrying no more than 100 volt-ampere (VA) per port without the need for special over-current
protection devices. POH also does not infringe on any of the mandated PoE safety requirements.
Looking at Practical Applications
PoH can be used to power a single-wire TV, considerably eliminating clutter in the living room. Audio, video, controls
and power are delivered through the same cable from an AV receiver, which can be placed up to 100m away. In this
case, the TV receives video, power, controls and Ethernet through HDBaseT. In another similar use case, it is possible
to have a two-box TV, in which most of the electronics and the intelligence is in the box, and the display is simply an
elegant flat screen which receives only video and power (see Fig. 3).
In another use case, PoH can be used in a two-box projector setup, where the projector powers both the transmission
box and charges the laptop with enough power that neither needs a separate power cord (Fig.4):
Conclusion
HDBaseT offers the unprecedented opportunity to merge uncompressed full HD digital video, audio, 100BaseT
Ethernet, power and various control signals onto a single 100m Cat5e/6 cable equipped with RJ-45 connectors and
POH power-delivery technology. POH is a key element of the HDBaseT standard, and draws upon the same PoE
technology that has been proven in enterprise networking and IP-based security and surveillance systems for the
past decade. Now, this technology is being used to deliver a high-performance, high-quality consumer multimedia
experience at very low power-consumption rates.technology that has been proven in enterprise networking and
IP-based security and surveillance systems for the past decade. Now, this technology is being used to deliver a highperformance, high-quality consumer multimedia experience at very low power-consumption rates.
Source: https://hdbaset.org/wp-content/uploads/2016/06/Introduction_to_power_over_HDBaseT.pdf
