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came to light earlier this year several folks repeated bricked Arduinos from supplying 5V direct to boards.
I’ve been thinking about this issue sense you have been raising it a couple of times lately. I certainly understand the issue and warnings about linear voltage regulators can have if there is voltage on their output terminal but no voltage applied to their input terminal, even some very old datasheets for the classic 7805 chips show adding a diode across inputs and output pins for protection from that issue.
However think about the standard Arduino Uno behaviour when it’s being powered by USB only, The auto voltage selector circuit detects that there is no Vin voltage available so it turns on the FET switch to route USB +5vdc voltage to the board’s Vcc bus which is the same as the 5V pin. So in that case there is +5vdc being felt on the output pin of the on board +5vdc voltage regulator but the regulator of course has no voltage on it’s input as there is no Vin present in this case. So how is a different case then if someone is powering the board directly via the 5V and ground pins from an external regulated +5vdc voltage source?
If the newer type voltage regulator has a problem with applying external +5vdc to the 5V pin, I don’t see that having any electrical difference then if the board is being USB only powered?
I have never been a fan of powering a standard arduino board via the 5V pin, but that’s because of the issue of if you then plug the USB cable to the PC you are effectively ‘hardwiring’ (through the FET switch) the USB +5 to the external power supplies +5, never a good engineering practice to connect too different voltage sources together without some form of isolation. But in this case we are talking about the vulnerability of the on-board voltage regulator, and again I don’t see a different condition for the regulator between being 5V pin powered or USB only powered?
So random users reporting ‘bricked’ boards is not a new report, but if it can really be caused because the arduino folks changed the brand/model of the on-board voltage regulator we really should try and put that to rest one way or another? We should try and minimize possible myth from facts as best we can by whatever means we have available.
PS: And yes, like you my favourite way to power a standard arduino board with an external regulated +5vdc source is to take a spare USB cable, lop off the PC end and extract the power and ground wires and wire that to the external 5 vdc power supply. That way you get the advantage on the USB thermofuse and plus the auto-voltage circuit isolation will still function as designed if you care to take advantage of another external voltage source connected to the Vin circuit at the same time.