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I know that a USB 2.0 port can deliver 500 mA and USB 3.0 can deliver 900 mA.

Is this any different on a phone, because it is a smaller device? I was thinking maybe it would be a smaller amperage, like 100 or 200 mA?

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"how much current does a phone USB port deliver?"

It only delivers anything when in USB-OTG mode. This isn't as well-known as normal USB. This article describes USB-OTG power in more detail.

The OTG spec calls for at least 8mA and allows negotiation for higher currents if the peripheral needs more power. OTG devices can provide up to 500mA, but in realistic terms, handheld portable electronics don't have 500mA to spare for external loads. 100mA is a commonly accepted realistic maximum.

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  • \$\begingroup\$ Sorry, are you talking about a phone charger? \$\endgroup\$ – William Lee Jul 24 '15 at 9:44
  • \$\begingroup\$ Yes. If you mean specifically USB data ports on a computer, they will indeed be limited to 500ma. \$\endgroup\$ – pjc50 Jul 24 '15 at 10:11
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    \$\begingroup\$ Let me rephrase my question, how much current does a phone USB port deliver? \$\endgroup\$ – William Lee Jul 24 '15 at 10:23
  • \$\begingroup\$ See edit about USB-OTG. \$\endgroup\$ – pjc50 Jul 24 '15 at 11:04
  • \$\begingroup\$ So there are phones that will reject a 100 mA device? Even though (I think) 100 mA is guaranteed from all hosts in the original USB spec? \$\endgroup\$ – endolith Jul 5 '16 at 21:10

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