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Fixed Current Limiting for all USB Ports?

Discussion in 'General Electronics Discussion' started by fuji, Jul 15, 2016.

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  1. fuji

    fuji

    5
    0
    Jan 18, 2015
    I know that all USB ports have an output of 5v, but the output current can vary.

    "A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0. etc..."

    My problem is current limiting between 0.5mA to 3.5A or maybe even more as I learned because some USB ports can output different current levels. Can anyone recommend me a circuit or an IC just for this matter? I want to output a fixed current of 500mA on any USB port I connect my circuit to.

    Thanks.
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Where do you expect the 500mA to go when nothing is plugged in?

    You cannot make a USB port output a fixed current, the current it outputs will depend on what is plugged in. A constant current supply varies its voltage in order to control the current. But that would not be a USB port, since it must have a fixed voltage of 5V.

    Bob
     
    fuji likes this.
  3. Alec_t

    Alec_t

    3,007
    813
    Jul 7, 2015
    Perhaps you mean limit the current, rather than provide a fixed current?
     
    fuji and davenn like this.
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