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How much power do MacBook USB ports deliver?

I've see USB hubs with voltages like 5v, 12v, and 24v being made.

1. How much power are the USB 2/3 ports on the Mid-2012 MacBook Pro capable of?
2. Does USB 3 delover more power than USB 2?
3. How does a USB device regulate the power it gets from the MacBook Pro's USB ports? In other words, what happens if the port is generating 12v of power, but the device only needs 5v?

See https://support.apple.com/kb/HT4049 - USB 3.0 ports on the 2012 models are 5v. USB 2.0 ports on previous machines are 5V as well.

CLinton

USB ports are all 5 Volts DC.  Depending on the device, the Amperage (how much power flows) is important.  My experience is that iPads need a minimum of .8 Amps DC {800 mA (milliamps)}

From Apple:

USB 1.1 or USB 2 ports:

Up to 500 mA (Milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.

Apple computers with USB 3 ports provide:

USB 3 ports:

Up to 900 mA (milliamps) at 5 V (Volts) to most Apple USB peripherals and all USB peripherals not made by Apple in compliance with USB specifications.

This shows 2.1 Amps on USB 3.0

Powering peripherals through USB - Apple Support

USB 2.0, maybe 1.1A.

MacBook Pro (15-inch, Early 2011) - I'm currently running over 1.0A on my USB 2.0 port on a non-Apple device that needs it.

最後更新：2017-10-05 06:08:53

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