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I've been reading about power supply requirements for RPi and want to learn more about the practical limits in addition to the design limits. What is the power protection circuit (if any) on the micro-USB port, what is the maximum voltage it will tolerate?

I have set up a test power supply (using a bench power supply, 7.5A (18AWG) leads to a micro-USB headshell). So I can see the relatively exact supply details. I've measured the voltage at the RPi micro-USB, and noted a 0.1V cable loss at 5.5V supply, so I believe my test cable can carry sufficient power.

While exploring the under-power situations described in a lot of articles on the web, I've varied the input voltage from 5V to 5.5V (which seems stable), and briefly risked up to 6V without frying the RPi. I am interested to know at what point I can expect smoke.

RowanP
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The Pi is rated at 5.0 ± 0.25V. The PMIC (on modern Pi) has a MAXIMUM input of 5.5V - exceed this at your peril.

The "protection" circuitry consists of a combination of polyfuse, ideal diode and surge limiting diode, which varies on model (consult schematics for detail). The Pi3A+ has no ideal diode.

Schematics for most models are available.

See Raspberry Pi Power Limitations

Milliways
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The Pi 3 is protected by the SMBJ5.0A over-voltage suppressor, which has a breakdown voltage between 6.4 and 7.1V. So above 7.1V you are guaranteed to trigger the over-voltage protection.

If the protection works as designed, you'll see no smoke: the polyfuse will limit the current to a safe value. However, 7.1V is above the rated maximum voltage of 5V components on the Pi, so there's still a good chance those ICs will blow up before the voltage suppressor has a chance to act.

Dmitry Grigoryev
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