Can it use electricity of 3.3v to supply electricity?

[manabu7696]

[KevScott]

My understanding is as follows, note that I am not the board designer so there may very well be something I am missing.

From the schematic on https://forum.mhetlive.com/topic/8/mh-et-live-minikit-for-esp32/8 the board uses an ME6211 regulator. The datasheet for that can be found at https://datasheet.lcsc.com/szlcsc/Nanjing-Micro-One-Elec-ME6211C33M5G-N_C82942.pdf. Note that there does seem to be some discrepancies with the datasheet as it does not show a 3.3v output on the header (which there is) and shows two switches, when there is only one.

Assuming that is the regulator, the datasheet says it can support up to a maximum of 250mW for the package used (see the Absolute Maximum Ratings section). The 5V supply from USB goes through a shottky diode which will drop around 0.35V before it gets to the regulator. So with 5 volts - 0.35 volts - 3.3 volts = 1.35 volts voltage drop across the regulator, the maximum current it can supply (without exceeded the 250mW spec) is 250/1.35 = 185mA.

So if you are running the ESP32 with the wifi and bluetooth turned off, it will take up to 68mA (from table 8 in the ESP32 Datasheet). The CP2104 with take around another 20mA when connected to USB. So in theory, you have nearly 100mA to play with externally but lets add a safety factor and say you should limit yourself to 50mA. If you can run the ESP32 in a sleep mode, you will have a lot more power available to other devices.

Note that if you turn the wifi on, and it is having to run at maximum power (from table 17 in the ESP-32 datasheet) the current taken by the ESP-32 will be 240mA which exceeded the power rating spec of the regulator.