USB As A Power Source


Posted on Feb 5, 2014

The Universal Serial Bus (USB) has become a popular method of connecting computer peripherals. The original USB 1. 1 specification limited data rates to about 12 Mbits/sec. The updated USB 2. 0 spec increases those rates to up to 480 Mbit/sec. Both versions of USB can provide DC power to peripheral devices. This power form is the subject of this pag


USB As A Power Source
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e. USB is less expensive than FireWire because a dedicated FireWire controller chip set isn`t needed. The computer`s CPU does the USB controller function in software. Under good conditions, USB can work nearly as well as FireWire, but at sustained high data rates, USB will sag under the strain. FireWire tends to work better but cost more therefore USB 2. 0 is more common, especially in lower end hardware. The USB 2. 0 specification can be found at the link. For reference, a link to the USB 1. 1 specification can be found at the bottom of the referenced page. Besides a data link, USB provides 5 +/- 0. 25 volts to power an otherwise unpowered device or charge a battery in a self powered device. A USB controller or hub is required to power one unit load (100 mA, a low power load). It can optionally power up to 5 unit loads (500 mA, a high power load). The spec is silent about intermediate loads, so I assume that the sources deal with just the two cases. Either a load is low power (like a keyboard or a mouse) or high power (like an iPod or PDA). Each USB device requires some way to power it. The device may run entirely from the USB port such as a jump drive does. Some devices have internal batteries that need charging. In any event, as the number of USB devices that I`ve collected has increased, management of an individual charger for each device is becoming a pain in the backside. Since the USB power form specification is a...




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