Moze i preko 500mA bez pregovaranja ako su novije ploce. To je ukratko, a malo sire je:
Charging ports
The Battery Charging Specification of 2007 defines new types of USB ports, e.g., charging ports.[41] As compared to standard downstream ports, where a portable device can only draw more than 100 mA current after digital negotiation with the host or hub, charging ports can supply currents above 0.5 A without digital negotiation. A charging port supplies up to 500 mA at 5 V, up to the rated current at 3.6 V or more, and drop its output voltage if the portable device attempts to draw more than the rated current. The charger port may shut down if the load is too high.
Charging ports exist in two flavors: downstream charging ports, supporting data transfers as well, and dedicated charging ports, without data support. A portable device can recognize the type of USB port from the way the D+ and D- pins are connected. For example, on a dedicated charging port, the D+ and D- pins are shorted. With downstream charging ports, current passing through the thin ground wire may interfere with high-speed data signals. Therefore, current draw may not exceed 900 mA during high-speed data transfer. A dedicated charge port may have a rated current between 0.5 and 1.5 A. There is no upper limit for the rated current of a downstream charge port, as long as the connector can handle the current (standard USB 2.0 A-connectors are rated at 1.5 A).
Before the battery charging specification was defined, there was no standardized way for the portable device to inquire how much current was available. For example, Apple's iPod and iPhone chargers indicate the available current by voltages on the D- and D+ lines. When D+ = D- = 2V, the device may pull up to 500mA. When D+ = 2.0V and D- = 2.8V, the device may pull up to 1000mA of current.[42]
Dedicated charging ports can be found on USB power adapters that convert utility power and/or another power source (e.g., a car's electrical system) to run attached devices and battery packs. On a host (such as a laptop computer) with both standard and charging USB ports, the charging ports should be labeled as such.[41]
Ovo je sa stranice:
http://en.wikipedia.org/wiki/USB
Poz,
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USB struja napon...
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