Power over HDMI cable eliminates the need for a separate power connector for active HDMI cables

TL; DR: Longer active HDMI cables usually have a micro USB or USB-C connector to power the internal chipset used for signal amplification. These ports will no longer be needed if you get a cable and a source device that are both certified to support power over HDMI.

The HDMI Forum has just announced a new amendment to its HDMI 2.1a standard. It adds support for HDMI power-over, which will allow active cables to draw power directly from the connector without the need for a separate power cable.

Passive HDMI 2.0 cables can extend 10 meters while maintaining maximum bandwidth support. The new HDMI 2.1 specification has nearly tripled the maximum net data transfer rate, but that comes at a cost. Currently, the best passive cables that support full 48 Gbps can reach around 3 meters before running into trouble with signal attenuation.

If you need to go further than that, active cabling is the way to go. These have chips and retimers inside that work together to reduce signal jitter. Standard HDMI cables are designed to carry up to 50mA, which is usually not enough to power their internal circuitry.

Power over HDMI increases this limit to 300mA at 5V, eliminating the need for a separate USB connector for power. Essentially, active cables with PoE support will plug in like passive cables, except they’ll be unidirectional, with one end only plugged into the source and the other only into the display.

Finally, the source device must also support the power specifications of the HDMI cable. The HDMI Forum says consumers should check a device’s specifications or packaging to determine if the feature is supported.

Alan A. Seibert