USB battery charging

摘要

One of the best, but least celebrated, features of the USB standard is the power supplied from the host to plugged-in USB peripherals. This enlightened change from the serial and parallel ports of the past allows a dramatic increase in the variety of devices that can be conveniently connected to a PC. Besides directly powering USB devices, one of the more useful functions that can be performed with USB power is battery charging. Because many portable devices, such as MP3 players and PDAs, exchange information with PCs, device convenience is significantly enhanced if battery charging and data exchange take place simultaneously and over one cable. Combining USB and battery-powered functionality gives rise to a whole range of untethered devices like removable web cameras that operate whether or not connected to a PC. In many cases, it is no longer necessary to include the ever-present and awkward AC adapter.