Hello,

I attached two schematics.
My first question is about the schematic with the red and blue squares.
What does the transistor see in its collector when a low signal goes into the base?

My second question is about the blue square. You can see the other picture to realize that those pins are the emitters of the low transistors.
Can I remove those resistors and just plug the emitters to ground since I don't need to sense current?

Thank you.

 

captura1- red square. Transistor is PNP, so conducts 14.3V between EC junction. The diode-drop (about .7), is 15-.7 = 14.3 when the base is grounded (held low).

captura2- blue square. The 6 resistors that are connected to the base of each transistor is to limit the amount of current on the base of the transistor (so it doesn't fry). The 3 other resistors shown in the drawing don't relate to this.

 

captura1- red square. Transistor is PNP, so conducts 14.3V between EC junction. The diode-drop (about .7), is 15-.7 = 14.3 when the base is grounded (held low).

captura2- blue square. The 6 resistors that are connected to the base of each transistor is to limit the amount of current on the base of the transistor (so it doesn't fry). The 3 other resistors shown in the drawing don't relate to this.

Thank you.

Would it be the same in this case when we have a mosfet? (new picture attached)

 

Not sure exactly what you're asking, but if I look at Cap1.png, I see a 15V signal that goes through a 10.2K-Ohm resistor then through the Drain and Source of the MosFET. If you are asking if the resistor can be removed-- NO. that resistor's purpose is to lower the current on that line to 1mA and prevent you from shorting 15V to ground when the MosFET connects Source and Drain.