- The USB 3.0 standard socket provides between 4.4 and 5.25 volts of DC at up to 900 milliamps of current. The earlier USB 2.0 socket, while physically compatible with the newer standard, provides up to 500 milliamps of current. The electricity can power a thumb drive--type memory stick, digital camera, cellphone and many other kinds of electronic devices and accessories.
- The standard automotive cigarette lighter socket provides 12 volts DC from the vehicle's electrical system at a few amps of current. Originally designed to provide current for an electrically heated cigarette lighter accessory, the same receptacle now sees more use as a power source for mobile electronic devices. A cylindrical adapter plug, designed to fit the socket, connects to its electrical contacts. The outward-facing end of the plug holds one or more USB sockets, providing electronic devices with power.
- Inside the adapter is a circuit called a DC-DC converter that changes the 12-volt vehicle electricity to 5 volts for USB devices. This is necessary because the higher voltage from the vehicle's electrical system is too high for USB devices. The current from the cigarette lighter is sufficient to power several USB outlets at the same time; some converters have up to four USB sockets on them.
- On a computer or mobile device, USB delivers both power and data communications. The cigarette lighter adapter provides only power for operating and recharging cellphones and other mobile equipment on the go; it has no data capability.
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