# NPN transistor base voltage supplied

Discussion in 'Homework Help' started by Legomaniac2311, Oct 5, 2014.

1. ### Legomaniac2311 Thread Starter New Member

Oct 2, 2014
14
0
I have a homework problem where I am given the value of VCC (10V) and the value of RE (1Kohm) and I am supposed to determine the value of the voltage going into the base to cause the transistor to enter saturation and cuttoff.

can someone please explain how to do this?

2. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,974
617
You are also given transistor data. For example, my textbook used 2N2222 as a standard transistor for all the excercises, the 2N2222 datasheet was included in the textbook.
So.
List again what you have.

3. ### Legomaniac2311 Thread Starter New Member

Oct 2, 2014
14
0
The hand out we were given doesn't specify any specific transistor we are supposed to use.

the only thing given is the VCC input and the value of RE.
the handout given to us just says that vi is a range of voltages. we are looking for the most positive value to cause cutoff and the least positive to cause saturation.

4. ### blah2222 Well-Known Member

May 3, 2010
574
36
What I gather from this is that you have an NPN transistor with the collector tied to Vcc (10V) and the emitter tied to ground through Re (1k), and finally a variable voltage source between the base and ground.

With no specific transistor data, you can assume that if the transistor is conducting, it will have a Vbe ~= 0.6V. With that known, you need to find out what base voltages (supplied by the variable voltage source) will cause the transistor to become saturated/cutoff. To figure that out, you need to use the following:

Forward-active: Vc > Vb > Ve
Saturation: Vc < Vb > Ve
Cutoff: no current flow

5. ### Legomaniac2311 Thread Starter New Member

Oct 2, 2014
14
0
so basically anything above 10V applied to the Base voltage source is going to drive the transistor into saturation.
And for cut off 0V or a negative voltage would drive the transistor into cutoff?