- #1

Peter Alexander

- 26

- 3

Hi,

before you proceed with reading this question, I would like you to know what I do not expect anyone to solve this task for me. I have a problem with a single step in the solution and I'm only asking you to help me with this one step.

Compute ##R_B## so that Q-point of given bipolar junction transistor is between the saturation region and the active region.

Other data: ##U_{BE} = 0.7 \text{V}##, ##U_{CC} = 5 \text{V}##, ##R_C = 1 \text{k}\Omega## and ##\beta = 100##.

Attached file includes a circuit in question.

This task should be solved with Kirchoff's laws easily. The reason why I'm saying this is because I've had a similar task before and it didn't require equations usually associated with bipolar junction transistors (e.g. Ebers-Moll model)

To keep it short and simple:

I started this task by looking at$$U_{CC} = I_C R_C + U_{CE}$$and$$U_{CC} = I_B R_B + U_{BE}$$which leads to a question: what about ##U_{CB}##?

From the first equation I can derive ##I_C## and use ##I_C = \beta I_B## to compute ##R_B## from the second equation.

My computations yield the correct result, but it is obvious that ##U_{CB} = 0## for this to work. I don't know why is that the case, and I'm not satisfied with "it has to be done in order to find the solution".

If someone would be kind enough to help me out, I'd very much appreciate it.

before you proceed with reading this question, I would like you to know what I do not expect anyone to solve this task for me. I have a problem with a single step in the solution and I'm only asking you to help me with this one step.

1. Homework Statement1. Homework Statement

Compute ##R_B## so that Q-point of given bipolar junction transistor is between the saturation region and the active region.

Other data: ##U_{BE} = 0.7 \text{V}##, ##U_{CC} = 5 \text{V}##, ##R_C = 1 \text{k}\Omega## and ##\beta = 100##.

Attached file includes a circuit in question.

## Homework Equations

This task should be solved with Kirchoff's laws easily. The reason why I'm saying this is because I've had a similar task before and it didn't require equations usually associated with bipolar junction transistors (e.g. Ebers-Moll model)

## The Attempt at a Solution

To keep it short and simple:

**I can only solve this task correctly if ##U_{CB} = 0## and I don't know why.**I started this task by looking at$$U_{CC} = I_C R_C + U_{CE}$$and$$U_{CC} = I_B R_B + U_{BE}$$which leads to a question: what about ##U_{CB}##?

From the first equation I can derive ##I_C## and use ##I_C = \beta I_B## to compute ##R_B## from the second equation.

My computations yield the correct result, but it is obvious that ##U_{CB} = 0## for this to work. I don't know why is that the case, and I'm not satisfied with "it has to be done in order to find the solution".

If someone would be kind enough to help me out, I'd very much appreciate it.