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I am designing a PCB for an Arduino Nano. I want to protect the Nano from over current and high voltage. In the schematic of the Nano, there is only one fuse at USB Vcc at Arduino Nano Rev3. No clone versions have fuses, either.

Why is there no fuse on the Vin pin of the Arduino? In my opinion, the Vin pin is more dangerous than USB Vcc.

For example, if powering an Arduino Nano clone from Vin pin with a 12V adaptor, a small diode in the bottom of the Nano starting to smoke immediately. I wonder if the fuse on the USB side is put to protect the computer?

The Arduino Mega is also only fused on the USB Vcc pin.

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JRE
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mehmet
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    A fuse does not protect from overvoltage or overcurrent. It basically just protects the wires if there is too much current for a short period of time. The electronic components may already be damaged when fuse blows. And hobbyists accidentally short things every now and then. Most of the time a PC USB output or external USB supply have some current limiting built into them.so they don't get immediately damaged if there is a short. So having a fuse on Arduino would just end up blowing up and render the board useless. Who would replace SMD fuses for example. – Justme Nov 05 '22 at 18:30

2 Answers2

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As you suspect, it's there to stop you from overloading the connected PCs USB port if you were for example to short the +5V pin to GND. Even though it is only basic protection, it was probably judged to be worth the extra component cost.

The level of protection provided to the USB port is very minial here, if you were to accidentally connect e.g. 12V to the +5V pin you'd quite likely fry the USB port regardless of the fuse (I know somebody who blew up their laptops only USB port doing just that).

A thorough design would also have other protections - fuse on Vin, TVS diodes, etc. - see for example Ruggeduino. However, given the Arduino is very much intended to be a low cost learning tool, the extra component cost for such protection circuitry probably couldn't be justified.

Tom Carpenter
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We have two power sources for the Arduino board: The 5V USB supply and the unregulated Vin supply. In fact, both power sources are current limited because Vin can't be directly applied to the microcontroller. Instead a low dropout regulator (LM1117) is used to convert it to 5V. Let's have a look into the datasheet:

The LM1117 offers current limiting and thermal shutdown. Its circuit includes a Zener trimmed bandgap reference to assure output voltage accuracy to within ±1%.

So no need for a second fuse if the LDO does the job as well. This is even better than a fuse as the regulator will limit the current without burning out like a fuse. Keep in mind that it stops at 800mA in contrast to the 500mA of the fuse.

I want to protect NANO over current and high voltage

Please note that we only have over current protection thus far. High voltage protection could be realized with something crude like a crowbar circuit or something more fancy.

JRE
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Gnarflord
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  • Would there be any sense in having a (P)PTC polyswitch resettable fuse in addition to the linear regulator? – The Lamb Dec 23 '22 at 07:50