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USB Power Specifications |
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| Generally, an USB connection provides five volts on
a single wire that the USB device can draw power from.
This setup can not provide more then 5.25 volts and no
less then 4.35 volts. |
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| When a device is connected, it is allocated 100mA of
power. After initializing, the device can request more
power in 100mA units up to a maximum of 500mA. Most ports
are able to provide the maximum amount of power. If the
device requests more power then the port can provide,
it will no be allowed to operate until the user rearranges
the network situation to provide more power. |
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| When a bus-powered hub is used, the maximum power provided
to each device is 400mA. This limits the hub to no more
then four users. If a device needs more power then can
be provided, it must utilize its own power supply to compensate
for the amount of power needed. The operating system keeps
track of the power requirements and specifications and
my alert the user when there is a power supply problem. |
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