WHAT IS POWERED USB?

Standard USB allows peripheral devices to exchange data with a PC and also to receive device power over the USB bus. Bus power is very convenient as it can save a power supply for each bus-powered peripheral device, power strips, and more complex electrical installation. These extra costs can often add $100 or more per POS station.

Unfortunately, the USB 1.1 and USB 2.0 protocols limit bus supplied power to 2.5 Watts (0.5A @ +5V) per port. For low power devices such as a keyboard or mouse, this is more than enough power. The USB standard also defines support for higher current devices up to 500 mA, but the total power limit is still 2.5 Watts. For higher power devices such as printers or displays, standard USB ’s power limit is often insufficient, requiring such peripherals to use an external power supply. This limitation takes away from the true “plug-n-play” idea conceived for USB peripherals. It also proliferates power bricks, wires, and higher installation costs.

Because of standard USB’s power limitation, IBM, NCR, and FCI/Berg jointly developed a way of expanding the USB 1.1 and USB 2.0 standards, increasing the maximum current as well as the voltage for bus-powered peripheral devices. This new design is called USB PlusPower or simply powered USB.

The USB PlusPower design provides the following voltage and current options:

• +5 volts DC at up to 6 amps per connector (up to 30 Watts)
• +12 volts DC at up to 6 amps per connector (up to 72 Watts)
• +24 volts DC at up to 6 amps per connector (up to 144 Watts)

The USB PlusPower design also includes a new USB cable design with two additional wire pairs inside the cable and modified connectors to support the new current and voltage. The new connector is backward compatible with the standard USB connector, so powered USB products also support traditional USB connections with no setting changes required.