ESP 32 auto reset transistor design

[Kentfielddude]

I have seen some esp32 designs which have 1k resistors connected to the auto reset transistors and esp32 pico design have 10k resistors on transistors. Do you know if it makes a difference?

[seonroz]

The resistors are just biasing resistors and to drop current between the base and emitter. 10k is a common value for biasing in something like an auto-reset as the transistors isn't being used to amplify current, but just as a signal level switch, so a higher resistor means less saturation on the base. I guess some transistors don't need such high values... definitely check the datasheet for the transistor you pick to ensure you are using an appropriate value.

Cheers,

[Kentfielddude]

Thanks. I've seen some designs using UMH3N dual transistor with 4.7k pre-bias which eliminates the need for the 10k external resistors.

[seonroz]

Thanks. I've seen some designs using UMH3N dual transistor with 4.7k pre-bias which eliminates the need for the 10k external resistors.

Yup, exactly the same circuit, just all inside the die to save space and component count, though not always cheaper to go that way.