USB and External Power Conflict ?

Thread Starter

Fran3

Joined Mar 28, 2019
21
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...
https://dl.espressif.com/dl/schematics/esp32_devkitc_v4-sch.pdf
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
 

Irving

Joined Jan 30, 2016
2,111
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

Fran3

Joined Mar 28, 2019
21
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.
 
Top