Transistor selection

[Maciek12]

I have a 3V3 switch key when the transistor's gate is 0. Which transistor should I choose here?

[Wimberleytech]

I have a 3V3 switch key when the transistor's gate is 0. Which transistor should I choose here?

That is a bipolar transistor.  The terminals are Emitter, Base, Collector.
If it were a MOSFET, the terminals would be Source, Gate, Drain.

What are you trying to accomplish here?

[Maciek12]

There is 0V or 3.3V at the thistor base (3V3_BAT)
I want the 3V3 (3V3) voltage from the collector to turn on when the base is 0V and power the processor (3V3_Out)


I do not know how to prepare such a key and which one to choose.

[ebclr]

This transistor on the schematic does not have a gate, has a base.  This application is so simple that any Bipolar transistor ( NPN) will work. Note that your output 3.3 V will go via a 10K resistor, This means your processor must push very low current, otherwise, your 3.3V will be consumed entirely on the 10K resistor. If that is the case you will need to decrease the 10K resistor a lot, Or even add a second PnP transistor to have a low impedance path

[Maciek12]

If it will be ok?
In datasheet Ic=100mA, so I choose R14=33R
                   Ib=5mA, so I choose R13=660R

It will be correct?
I only want simple transistor key
Vb=0, so Vout=3V3
if
Vb=3V3 then Vout=0

[ebclr]

Rbase must Be (3.3 - 07) / ( 0.1 A * transistor beta )

You output tension will never be 3.3V , Will be 3.3 - ( emitter resistor * 0.1 A + you output current consumption )

Also will never be 0, Will be VCE saturate topically + 0.25V

[Maciek12]

What and how to apply to get 3V3 output?

[Wimberleytech]

See fig

[Maciek12]

Can I use BC857BLT1G in this configuration?

[Wimberleytech]

Can I use BC857BLT1G in this configuration?

No.  That is an NPN.  You need a PNP in the circuit I drew.

[Maciek12]

https://www.tme.eu/Document/1a1e3af2539579d004bcdd8b7742a187/BC856ALT1-D.PDF

Here is information that it is pnp

[Wimberleytech]

https://www.tme.eu/Document/1a1e3af2539579d004bcdd8b7742a187/BC856ALT1-D.PDF

Here is information that it is pnp

That will work.  Maximum collector current continuous is 100mA.

[StillTrying]

There is 0V or 3.3V at the thistor base (3V3_BAT)
I want the 3V3 (3V3) voltage from the collector to turn on when the base is 0V and power the processor (3V3_Out)

If the 3V3 out really is to power a processor rather than just provide a logic level input you could do with knowing how many mA the processor needs, it might only need a few mA, but it could also be a lot more than 100mA.