USB and External Power Conflict ?

Thread Starter


Joined Mar 28, 2019
Just received...
1 - ESP32-DEVKITC32D by Espressif via Mouser
2 -ESP-WROOM-32 ESP32 ESP-32S Development Board by HiLetgo via Amazon

Seems either can be powered via USB or External 5 Volt Supply.

Question is: Can you connect both at the same time?

Below is the circuit connecting the USB 5 Volts and the External 5 Volt Supply to the internal circuits on the ESP32 Dev Board...
As I see it the diode blocks the External Supply from connecting to the USB 5 Volts...
But if the USB 5 volts is greater than the External Supply current would flow from the USB 5 volts to the External 5 Volt supply.
I haven't designed circuits in a long time but shouldn't they have placed a diode in series with each supply before connecting them together?
Actual diagram is here...
Below is my simplified drawing of that power input circuit...
Thanks for any help as I don't want to blow up my new ESP32 Development boards :) PS - Possible reason for connecting both USB & External 5 Volt Supply...
In the event the application requires more current than the computers USB port can supply
and you don't want to unplug the computer with the IDE and/or interface from the USB port while you test.

ESP32 External Power.png


Joined Jan 30, 2016
The diode is there to stop ext 5v from powering the USB line as thats a no-no in the USB standard. The USB 5v will never be > 5.25v and so for all normal situations ext_5v will reverse bias the diode and will be the source of power. If there is a issue with ext_5v being driven then you are at liberty to add your own diode but its generally not needed.

I think you'll find, if you look carefully, the only place is used is on the UART as an indicator that the USB is active. Its not used as a supply (other than via Ext_5v) or brought out on any pin.
Last edited:

Thread Starter


Joined Mar 28, 2019
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.