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You can power the Arduino Uno/Nano using the following:

  • Barrel Jack (for UNO only), it is connected to the input to voltage regulator.

  • VIN pin, it is also connected to input of voltage regulator.

  • 5V pin, it is connected to the output of the voltage regulator and directly of 5V of Atmega MCU.

  • Finally, the USB.

Is the positive supply of the USB port of an Arduino is connected to the 5V directly? I tried to use a connectivity test using multimeter but it is not connected.

Moreover, it is mentioned in the Arduino documentation around the internet that if you powered the Arduino via USB connection, the 5V pin will be limited to 500 mA only. What if I use an AC to DC adapter (2A output current) that is connected to the USB port of the Arduino, will I will still get only a max of 500 mA? Or if I use USB 3.0 that can supply 900 mA, will I still get 500 mA max for the 5V pin? I read that the polyfuse is the one that is limiting that current.

I have used Arduino Uno and Nano for a long time but I just became aware of this basic concepts when I made a project that should compute the overall power consumption of the device.

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closed as too broad by Chris Stratton, RoyC, Sparky256, Voltage Spike, Bimpelrekkie Mar 15 at 9:18

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ Would this be more suited for arduino.SE? Given that it's a question specifically about the Arduino hardware and not electrical engineering in general. \$\endgroup\$ – Hearth Mar 11 at 0:36
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    \$\begingroup\$ why don't you look at the arduino schemattic? \$\endgroup\$ – jsotola Mar 11 at 1:53
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  1. There are a lot of "Arduino-compatible" boards which are sold as "Arduino" labeled. The schematic is common in general, but can be different in details. You should investigate what do you have on you specific PCB yourself (or post detailed images of the both sides of the board here).

  2. I think, 500 mA limit comes from two factors:

    a) USB 2.0 specification (500 mA max);

    b) Some of the "Arduino-compatible" boards have fuse on USB power line of the same 500 mA value (but your specific board may not have it). Or, let say, the diode which can handle 0,5 A only.

  3. "Normally" when your device (Arduino board + additional modules etc.) does some useful job you should power it from one definite source - USB or power supply. And you have to decide yourself how to power it correctly. Also powering from USB can be made from computer USB port or from power supply with USB output. The choice is up to you.

You can also unsolder fuse or diode from you PCB and then you'll get (almost) no limits to power current from USB input (but you'll get the risk of frying you USB port also, if something goes wrong on the PCB side).

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  • \$\begingroup\$ Dont know for all PCs (motherboards), but when I mistakenly want to use more than 500 mA from USB port, OS promptly informed me that usb device malfunctioned, but nothing bad happened to PC side. So there may not be any risk to damage usb port. \$\endgroup\$ – Rokta Mar 11 at 10:15
  • \$\begingroup\$ @Rokta I have burned myself at least 2 USB ports several years ago. :) One of them was when I experimented with my implementation of software USB on ATmega8. And I have never see this kind of message, even when I plugged 1 A external USB HDD to 500 mA USB port (it didn't work, but there was no damage to motherboard either; also there were no massages from OS). So yes, probably this is manufacturer/model dependent, but we should consider the worst case. \$\endgroup\$ – cyclone125 Mar 11 at 10:41
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Uno has a 500mA resettable fuse similar to this between the USB 5V supply and the 5V pin on the header. A PFET is used to keep 5V from the board from driving back into the PC. It is located near the USB connector

enter image description here

https://www.digikey.com/product-detail/en/bel-fuse-inc/0ZCG0050AF2C/507-1762-1-ND/4156148

Nano has a diode between USB 5V and the regulator output so that the PC cannot be driven from the board.

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Not all of them are, get a Digital Multi Meter out and ohm out the lines, if they are under 1 ohm then there is a good chance that they are connected directly. Some times Eval boards put DC to DC converters between the USB and device.

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