Powered USB
- This article is about the proprietary variant USB standard. Self-powered conventional USB devices may also colloquially be referred to as "powered USB"; cf. e.g. self-powered USB hubs.
Powered USB, also known as Retail USB, USB Plus Power, and USB + Power, is an addition to the Universal Serial Bus standard that allows for higher-power devices to obtain power through their USB host instead of requiring an independent power supply or external AC adapter. It is mostly used in point-of-sale equipment, such as receipt printers and barcode readers.
Powered USB, as a proprietary variant of USB, was developed by IBM, NCR, and FCI/Berg but is not endorsed by the USB Implementers Forum (USB-IF).[1][2] IBM, who owns the patents to Powered USB,[3][4] charges a licensing fee for its use.[5]
Powered USB uses a more complex connector than standard USB, maintaining the standard USB interface for data communications and adding a second connector for power. Physically, it is essentially two connectors stacked such that the bottom connector accepts a standard USB plug and the top connector takes a power plug.
The implementation allows a choice of three different voltages, providing power at 5 V (30 W), 12 V (72 W), or 24 V (144 W). The three voltages are able to operate at up to 6 A. USB 1.0 and 2.0 supplies 5 V at up to 0.5 A (2.5 W).[6] USB 3.0 supplies 5 V at up to 0.9 A (4.5 W).[7]
As each Powered USB plug provides one of three voltages, the plugs come keyed in three versions so they will only accept connections from devices requiring that version’s voltage.[2]
Extending USB's power capability is a response to Power over Ethernet which has more flexible dynamic power negotiation capabilities up above 48 V DC and up to about one amp, and whose maximum bandwidth is potentially greater than USB 3.0's once the 10 Gbit/s Ethernet standard is supported. The combination of USB 3.0 and a 6 A limit at the most common (5, 12, 24 V DC) voltages permits support of a wider variety of devices, although powered Ethernet can support them at longer cable distances, power loss in small DC voltages are very significant over even a few meters, so it is unlikely that powered USB can compete over longer distances effectively.
[edit] References
[edit] External links
- http://www.poweredusb.org — An informational website
