I have a issue with my Arduino Uno r3.

I'm not sure why is that happening but I have a 5 V, 18 A power supply to power my LEDs. I connected 5 V from the Arduino to 5 V from the external power supply and I plugged this combined cable to my LEDs. I did the same with GND. On data pin 6 I used a 220 Ω resistor. Also I am using a 12 V power supply to power my Arduino.

At the same time the USB was plugged in.

In and between USB and power some chip is getting hot. I got scared and unplugged the whole Arduino. I am not sure how I should plug this in. It worked fine until I plugged in the external power supply and I was using few LEDs at the time.

This is what it looked like in more understandable way.

this is what it looked like in more understandable way

Please point out to me what I did wrong.

  • 1
    If you a separate 5V 18A power supply for supplying to the LED, then there is no need for the 12V power supply as you already connect the power supply to the 5V pin of the Arduino board as per your drawing.
    – hcheung
    Aug 30, 2022 at 0:29
  • Rule #1: A Power Supply the Arduino is NOT!
    – Gil
    Aug 30, 2022 at 19:48

2 Answers 2


I suggest you do not use the 12V external power when you are already supplying it with an externally regulated 5V source.

The sole purpose of the 12V input is to provide a 5V regulated supply voltage for the microcontroller. The PCB outputs this on the 5V header. The problem is that you are feeding your external 5V into that pin.

You can either continue powering the Arduino from the 12V supply and disconnect the external 5V from the Arduino (keep the GND from the external 5V conected). Or you can just remove the 12V power source.

It could end up that you have damaged the chip that overheated. If the Arduino still works after doing one of the solutions above, then you may be lucky and not damaged anything.

As a precaution, please measure your external 5V source with a multimeter to make sure it is within specs that Arduino allows.


yes, as the other people say. I'm an electronician , your power supply 5V 18 Amperes , it's to dangerous to connect that to your arduino, the board is not creating to support a great power, if someone of your outputs receives all this unlimited power P = U × I = 5 × 18 = 90 Watts, your board is just able to smell a awful odour. yes, your board burnst with thi great possible intensity. 1. Connect all the several ground together and for supply the arduino take on the USB header . 2. connect your power supply directly on the leds board. warning test that, but it is possible that your board working not more, see all the led of your board and detect step by step if it works normally...

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