ESP32 Forum

Hello everyone.

I want to power an ESP32 S3 Zero with an external 3.3V power supply when it is not connected to the USB. According to the schematic, the USB has no protection, so I must connect a Schottky to the 5V pin myself.

My idea is to isolate both 3.3V and allow the external 3.3V only when the USB is turned off.

What do you think?

Thanks.

That won't work. Q8 is a P-channel mosfet, so it allows 3.3V through when its gate is at ground level. Meanwhile, Q7 will ground that gate when 5V is applied; so you're getting the exact opposite behavior compared to what you intended. You probably want to remove Q7 and connect D4 directly to the gate of Q8.

That won't work. Q8 is a P-channel mosfet, so it allows 3.3V through when its gate is at ground level. Meanwhile, Q7 will ground that gate when 5V is applied; so you're getting the exact opposite behavior compared to what you intended. You probably want to remove Q7 and connect D4 directly to the gate of Q8.

Hello,

Thank you very much for your answer.

Basically what I need is that when the zero is connected to the USB, the MOSFET cuts off the supply of EXTERNAL3V3 to avoid conflict. But at the same time, PIN3V3 cannot pass to EXTERNAL3V3.

Best wishes.

First of all, you probably want to keep R8 from your original schematic, as well as flip D4 around.
Second of all, you cannot fulfill the requirement that the internal 3v3 cannot feed the external 3v3 with that schematic, as the body diode of the mosfet will allow current through that way.