I agree with your comments Irving. So, regardless of what I heard on another forum it should be OK to have the USB connected and an external 5 volt power supply connected to the ESP32 Development Board at the same time.
Thanks for your reply.

And it worked? To have the USB connected and an external 5 volt power supply connected to the ESP32 Development Board at the same time?

Moderator edit: New thread created from old thread.

 

Yes it does, though the second (external) supply must be happy having power fed in 'backwards'. Most 3-terminal linear regulators or switched buck converters are OK with this as they sense the voltage on their output and match it so pass no current themselves.

On some of my projects where I want the ESP32 powered all the time by the external supply, I set the output of the external supply slightly higher at 5.25 - 5.3v. This doesn't impact the ESP32 but ensures the diode between the USB and the 3.3v regulator is reverse biassed. You can easily tell that is the case with a USB power meter - it will show zero current flow from the USB side.

 

Most 3-terminal linear regulators or switched buck converters are OK with this as they sense the voltage on their output and match it so pass no current themselves.

That's true if they have input power , but 3-terminal regulators can be damaged by voltage on the output if they are unpowered.
To prevent that, a diode can be connected from the output (anode) to the input (cathode) as often shown in their data sheets.

Might be a good idea to do the same with a buck converter.

 

To prevent that, a diode can be connected from the output (anode) to the input (cathode) as often shown in their data sheets.

Good point. Though on most of mine where I've used a buck converter I've put a small schottky diode in series, which has the same effect. The ESP32 rarely draws more than 150mA. And in many cases I've not bothered with either and haven't experienced any issues...