This is a follow on from this question

Given a home made USB charger that simply provides 5 volts across the GND and VCC pins of a USB port, what should the default behavior be of any mobile device (mobile phone, tablet, iphone etc) plugged into that device. ('data +' and 'data -' left unconnected)

Will it...

  1. completely ignore the device (i.e. not charge at all)
  2. attempt to trickle charge very slowly at low current
  3. attempt to charge at a current of no more than 500ma
  4. attempt to charge at a current exceeding 500ma

I have read this but am no wiser.

  • 1
    \$\begingroup\$ are you really interested in "what should" or are you interested in "what does the majority actually do"? \$\endgroup\$ May 4, 2019 at 13:52
  • \$\begingroup\$ Answers to either or both would be good! \$\endgroup\$ May 4, 2019 at 15:08
  • 1
    \$\begingroup\$ yeah, but what is the purpose of your question? as it is, the answer will be "any of 1-4, depends on your USB device and how the supply behaves under load", so I'm afraid this question would be too broad. What USB-compliant devices should be doing is try to ask for more than 150 mA, and failing to do so, not draw more. Nearly nobody does that. On the other hand, without some smarts that signal fast charging ability to the USB device, very few devices will try to draw a lot of current. Now, this simply sounds like "don't call a 5V voltage supply a "USB charger", because it's not", but I'm \$\endgroup\$ May 4, 2019 at 15:23
  • 1
    \$\begingroup\$ sure there is a story to your question, with a sensibly answerable question hidden beneath! \$\endgroup\$ May 4, 2019 at 15:23
  • \$\begingroup\$ Try to search for "charger signature", for example: electronics.stackexchange.com/q/130559/117785 and electronics.stackexchange.com/a/271681/117785 and \$\endgroup\$ May 4, 2019 at 15:50


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