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Resistor Values for a USB Charger.

Discussion in 'General Electronics Discussion' started by QuestionablyHuman, Mar 13, 2017.

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  1. QuestionablyHuman


    Mar 13, 2017
    I want to build a USB charger for my iPhone. I know that for slow charging speeds on the data pins you need to have 2.0v each, which can be achieved by connecting a 75k resistor to 5v, connecting the data pin to that, and then connecting a 50k resistor from the pin to ground. I want to do fast charging, so one data pin on the USB port needs to be 2.0v and the other needs to be 2.7v. Does anyone know of the correct resistor configuration to achieve that from 5v? It's going to be a dedicated iPhone-only port, so cross-compatibility is not an issue. Any help would be very much appreciated!
  2. davenn

    davenn Moderator

    Sep 5, 2009
    welcome to EP :)

    google is your friend

    have a look through these links
  3. QuestionablyHuman


    Mar 13, 2017
    I've looked through everything and the only thing people seem to do is 2.0v and 2.0v. I really have no idea how to calculate the resistance or resistors needed.
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