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I'm reading about powering alternatives for the arduino board, and I have run across two confusing sentences in Section 5, powering via 3V3/5V pin. First, it says:

3V3 and 5V pins can also be used as power inputs if no regulated power supply is connected through the other power inputs (USB port, barrel jack connector or VIN pin).

But then right afterwards, it says:

Although 3V3 and 5V pins can be used as power inputs, it is not recommended if no power supply is connected through the USB port, the barrel jack connector, or the VIN pin.

(emphasis mine)

Which is correct? When powering via the 3V3 or 5V pin, should I have a different power supply connected elsewhere, or not?

Johnny Dollard
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  • they are both correct ... one says you can do this ... the second one says but it is not recommended that you do this ... similar to you can run across the street ... but it is not recommended that you run across the street .... they are basically saying don't use the arduino as a power supply if you can avoid it – jsotola Jul 24 '23 at 21:06
  • The issue appears to be backfeeding the voltage regulator which is connected to the 3.3v or 5v pins. Some voltage regulators don't like it (see https://electronics.stackexchange.com/questions/110314/how-can-i-tell-if-my-power-supply-regulator-will-accept-backfed-current). – 6v6gt Jul 25 '23 at 00:23

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