1

Many years ago, I've noticed that one without requirements of any 5V devices like USBs, he/she can completely bypass the power input circuit and the regulator. Feeding Pi Model A with power from v3.3 GPIO pin, and shorts 5v with 3.3v can be a practical solution.

I knew it should be proceed with caution since there was no protection, e.g. feed 5v to 3.3v could destroy it. I also found some nice measurements for it.

However, time passes and it's 2016 now. I do not know if the circuitry within Pi 2 or Pi 3 has been changed and made this approach insane. I wonder if it could fry some parts like the regulator.

Can I still power newer Pis (2/3) from 3.3v without any issues?

2

No. The SOC actually requires other voltages (especially 1.8V which runs most of the Pi). These are all derived internally from the 5V supply with a couple of switch mode regulators.

0

You can power the Pi with 3V3 provided you put the 3V3 into the 5V pin (i.e. don't short the 3V3 and 5V pins, connect your 3V3 power supply to pin 2 or 4).

The Pi itself will work quite happily.

Of course peripherals such as HDMI and USB which need 5V are unlikely to work.

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