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# How many USB ports would be required for 3 Watts of Power?

How many USB ports would be required for 3 Watts of Power?
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hankknight
4 Solutions

Commented:
From the info on the Wiki page,

2 standard USB ports or 1 USB3 port

"Standard USB hub ports can provide from the typical 500 mA/2.5 W of current, only 100 mA from non-hub ports. USB 3.0 and USB On-The-Go supply 1.8 A/9.0 W (for dedicated battery charging, 1.5 A/7.5 W Full bandwidth or 900 mA/4.5 W High Bandwidth), while FireWire can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical."

http://en.wikipedia.org/wiki/USB
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Author Commented:
So assuming:
Voltage: 5.00V
Current      500–900 mA (750 mA Average)

How many of those ports would it take for 3 Watts of power?
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Commented:
One (1).
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Commented:

It appears that you are missing the basic formula: P=E*I  (Power = Voltage * Current)
500mA * 5V = 2.5W
900mA * 5V = 4.5W
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Commented:
For complete details see
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http://www.ti.com/lit/an/slyt118/slyt118.pdf
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