Last time, when I supplied 12 V from a power supply to the Arduino's 5V pin, it blew up. This time I'm going to use an adapter. Why does an adapter with a 12 V input not blow an Arduino up, as in the previous case?

Or, should I have supplied 12 V to Vin pin, instead of the 5 V pin?

Edit: Sorry for saying 12V input, it is written 12V output and I meant a power adapter that is plugged into wall.

  • What sort of adapter are you talking about? Do you mean a power adapter that you plug into the wall, to convert 240 V a.c. mains electricity to 5 V d.c.? Apparently you aren't referring to a power adapter, as you say that the adapter has a 12 volt input, so do you mean a DC-DC convertor? Or do you mean a regulator, that reduces voltage from 12 volts to 5 volts (which, effectively, does the same as a DC-DC convertor)? Please edit your question to clarify. Commented Jun 1, 2017 at 13:03
  • 1
    Congratulations on confirming their design. That is exactly what it is supposed to do. When you feed more than 5V into the 5V pin it is specifically designed to melt down and never work again. I bend the pins inward to show they are n/w then give them to the kids to play with. Sometimes I turn up a few pins like they are eyes or horns. It makes a fun toy. Meanwhile, you have now discovered why they provide the Vin pin, which goes through a regulator. With that pin, 9-12 volts is just fine.
    – SDsolar
    Commented Jun 30, 2017 at 23:36
  • 12 Volts is fine into the barrel connector.
    – SDsolar
    Commented Jul 1, 2017 at 0:36

1 Answer 1


First of all you should read the tech specs for Arduino Uno here: https://www.arduino.cc/en/Main/ArduinoBoardUno

You will find this important information about power supply:

Operating Voltage   5V
Input Voltage (recommended) 7-12V
Input Voltage (limit)   6-20V

From documentation also:

Vin. The input voltage to the Arduino/Genuino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.

5V pin.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

So answering you question: yes you should have supplied 12v on Vin. Not on 5v.

Why does an adapter with 12V input not make the same blown up for arduino like in the previous case?

Because you are pluging 12v in the correct input, the 7-12v jack.

Another important link to read: http://playground.arduino.cc/Learning/WhatAdapter

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