Can I use the same BJT model in both positions?

Yes, almost all general purpose bjt should work (the ones that can handle up to 500mA)

 

If doing it, why not just use a Sziklai pair?

 

Deleted previous post, wrong resistors value:
View attachment 182013

2N2222 BJT Min hfe: 30

Can I use 12 V as signal in this circuit?

 

Can I use 12 V as signal in this circuit?

No, you'd have to recalculate resistors value

 

No, you'd have to recalculate resistors value

Ok, thanks.

 

No, you'd have to recalculate resistors value

When I turn the circuit on, the electromagnet conduct. But, I don't know why, when I set the 5 V signal on it doesn't cut of the electromagnet current. What can be happening, please?

 

Can I test somehow to see where are the problem?

 

When I turn the circuit on, the electromagnet conduct. But, I don't know why, when I set the 5 V signal on it doesn't cut of the electromagnet current. What can be happening, please?

Double check resistors value? Measure at the base of the output transistor, it should be less then 200mV when off.

 

WORKED. THANKS EVERYONE.

 

WORKED. THANKS EVERYONE.

Nice!

 

Although it worked, you should probably replace it with a mosfets version for less current consumption

 

The post #40 circuit will work if the power MOSFET is a logic-level type. If it's not, connect the top 10k resistor to +12V instead of to +5V.
(BTW, when drawing circuits, get into the habit of labelling each component, e.g. R1, R2 etc. It makes it much easier to discuss the circuit.)

If I use an IRF540 mosfet what tension I should use?

 

An IRF540 needs about 10V Vgs to switch on fully.

 

An IRF540 needs about 10V Vgs to switch on fully.

So, connecting the 10k resistor to the 12 V battery it's enough?

 

You'll need a bjt to drive it
Like this:

 

You'll need a bjt to drive it
Like this:
View attachment 182546

A 2N2222 can do it?

 

An IRF540 needs about 10V Vgs to switch on fully.

This circuit is ok?

 

A 2N2222 can do it?

yup

 

 

That question have been answered by Alec and was quoted in post #72. What dont you understand? Is the IRF540 a logic level mosfet?