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USB was designed to standardize the connection of peripherals to personal computers, both to exchange data and to supply electric power. It has largely replaced interfaces such as serial ports and parallel ports and has become commonplace on various devices.
12 V and 24 V powered USB sockets, on an NCR cash register. PoweredUSB, also known as Retail USB, USB PlusPower, USB +Power, and USB Power Plus, [1] 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.
To allow for voltage drops, the voltage at the host port, hub port, and device are specified to be at least 4.75 V, 4.4 V, and 4.35 V respectively by USB 2.0 for low-power devices, [a] but must be at least 4.75 V at all locations for high-power [b] devices (however, high-power devices are required to operate as a low-powered device so that they ...
The written USB 3.0 specification was released by Intel and its partners in August 2008. The first USB 3.0 controller chips were sampled by NEC in May 2009, [4] and the first products using the USB 3.0 specification arrived in January 2010. [5] USB 3.0 connectors are generally backward compatible, but include new wiring and full-duplex operation.
USB 3.0 port provided by an ExpressCard-to-USB 3.0 adapter may be connected to a separately-powered USB 3.0 hub, with external devices connected to that USB 3.0 hub. On the motherboards of desktop PCs which have PCI Express (PCIe) slots (or the older PCI standard), USB 3.0 support can be added as a PCI Express expansion card .
In 2012, the USB Power Delivery (PD) specification was released. Power Delivery provides the ability for 5 V devices to draw more than 7.5 W of power (the limit specified by USB Battery Charging) from USB PD-aware ports when using PD-aware USB cables. The specification also allows PD ports to provide even greater power at higher voltages over ...
The USB OTG and Embedded Host Supplement to the USB 2.0 specification introduced three new communication protocols: . Attach Detection Protocol (ADP): Allows an OTG device, embedded host or USB device to determine attachment status in the absence of power on the USB bus, enabling both insertion-based behavior and the capability to display attachment status.
A four-port "long cable" "external box" USB hub A four-port "compact design" USB hub: upstream and downstream ports shown. A USB hub is a device that expands a single Universal Serial Bus (USB) port into several so that there are more ports available to connect devices to a host system, similar to a power strip.