I have recently bought an Arduino Mega, and I am powering it with a USB charging port, 5V at 1A. I need to use the 1A with a transistor, since the Arduino itself can only supply a maximum of 20mA through one pin.
So I was wondering, is there any way to access this unregulated power source? Would the VIN pin serve this purpose, or is there no way to access the 1A current without pulling apart the USB cable?

1 Answer 1


The VIN port is connected to the barrel jack. It must only be used if you are powering the board through that jack.

To access the USB power just use the 5V pin - it is directly connected to the USB.

However, the USB, although the socket it is plugged into can supply more, is limited to 500mA. This is because of a 500mA auto-resetting polyfuse on the USB power input (the large gold and dark green rectangle next to the USB socket - mine has either XE05 or 503X on it depending on which way up you hold it).

  • Okay, thank you for clarifying. I guess I'll need to power it another way, so I can access the power source... or sacrifice a USB cable!
    – Nabushika
    Mar 21, 2016 at 19:41
  • The VIN port is connected to the barrel jack. - via a diode. Thus Vin will be around 0.7V less than what you supply at the barrel jack.
    – Nick Gammon
    Mar 23, 2016 at 20:22

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