What temperature rise causes the transistor to saturate?tran

[Jadejadeface]

Homework Statement

1. Additional Exercise 7 in the textbook (H&H, p. 110). Vout is 0.5Vcc at the quiescent point. You may assume beta = 100. The transistor is said to saturate when VC = VB. Use the fact IC grows 9%/ degree C and that VBE is constant to determine when the transistor saturates.

Homework Equations

Vb = Vbe +IeRe

Vcc = IcRc + Vce + IeRe where Ic = (beta x Ie)/(beta +1)

The Attempt at a Solution

Ok, so firstly I'm confused about whether we need to answer 7 and this question or just what's written in "1.". Anyway, for Vb = 0.5Vcc the two resistors must be equal ( I don't really understand what that arrow is pointing to the resistor, please explain? Since the problem says he adjusts it until 0.5Vcc is reached I'm assuming both resistors = 1K) Therefore Vout = 10V = Vb.

And this is as far as I get since there is no Re I'm not really sure about how to get Vc. If there was a resistor there I would find Vc using the above equation then figure how much I need to increase the temperature to get Vc = 10v. Please help!

Is the current in the collector the same as that in the emitter? Do I need to take into consideration re (little r e, the intrinsic resistance of the resistor)?

 

[KataKoniK]

Thank you for your post. I understand your confusion about the problem and I am happy to help you find a solution. To answer your question, yes, you do need to answer both the additional exercise 7 and the question in "1." In order to determine when the transistor saturates, we need to consider the equations you listed and also take into account the temperature coefficient of the transistor.

Firstly, we can use the equation Vb = Vbe +IeRe to find the value of Re. We know that Vb = 0.5Vcc = 10V, and Vbe is constant. Therefore, we can rearrange the equation to solve for Re. Once we have the value of Re, we can use it in the equation Vcc = IcRc + Vce + IeRe to find Vc.

Now, to take into account the temperature coefficient, we can use the fact that IC grows 9% per degree Celsius. This means that for every degree increase in temperature, IC will increase by 9%. We can use this information to find the temperature at which Vc will reach 10V. We can set up an equation where Vc is equal to 10V and solve for the temperature. This will give us the temperature at which the transistor will saturate.

I hope this helps. Please let me know if you have any further questions or if you need any clarification on the solution. Good luck with your studies!