calculate values from BJT I/O curve

WBahn

Joined Mar 31, 2012
30,057
You need to show YOUR best attempt to solve YOUR homework problem.

We can then use that as a starting point to help guide you from where you are to where you need to end up.
 

Thread Starter

M0GLI

Joined Sep 22, 2013
5
A good starting point would be to remember the definition of alpha and beta.
I know about alpha beta.I know about the I/O characteristics curve and BJT models. but how to draw load line and calculate those from curves, give me hints.I dont want you to solve this for me.just give me some clue
 

LvW

Joined Jun 13, 2013
1,756
I know about alpha beta.I know about the I/O characteristics curve and BJT models. but how to draw load line and calculate those from curves, give me hints.I dont want you to solve this for me.just give me some clue
Alpha and beta are transistor parameters - independent on any application. Thus - there is no "load line" to be considered.
 

LvW

Joined Jun 13, 2013
1,756
As another hint:
Are you able to determine the DC current gain B?
Do you know if there is a (considerable) difference between the dc current gain B and the differential current gain beta?
 

WBahn

Joined Mar 31, 2012
30,057
I know about alpha beta.I know about the I/O characteristics curve and BJT models. but how to draw load line and calculate those from curves, give me hints.I dont want you to solve this for me.just give me some clue
It's debatable that you know about alpha and beta and characteristic curves and BJT models if you don't have a clue about where to start or think that there is any kind of a load line involved in this problem at all.

So let's take it from the basics.

Q1) What is the definition of the DC beta?

Q2) For this transistor, what is Ic under the conditions specified in part i)?

Q3) Given Q1 and Q2, what is the answer to part i)?

Q4) What is the definition of alpha?

Q5) What is the relationship between Ib, Ic, and Ie?

Q5) Given Q2, Q4, and Q5, what is the answer to part ii)?
 

Thread Starter

M0GLI

Joined Sep 22, 2013
5
It's debatable that you know about alpha and beta and characteristic curves and BJT models if you don't have a clue about where to start or think that there is any kind of a load line involved in this problem at all.

So let's take it from the basics.

Q1) What is the definition of the DC beta?

Q2) For this transistor, what is Ic under the conditions specified in part i)?

Q3) Given Q1 and Q2, what is the answer to part i)?

Q4) What is the definition of alpha?

Q5) What is the relationship between Ib, Ic, and Ie?

Q5) Given Q2, Q4, and Q5, what is the answer to part ii)?

1) answer: base to collector dc curent gain
2) answer: Ic= 1.4mA (from the curve)
3) answer: beta dc= Ic/Ib = (1.4mA/10uA)= 140
4) answer: Ie=Ib+Ic
5) answer: Ie= Ib+Ic= (1.4mA+10uA)= 1.41mA
alpha= Ic/Ie= 1.4mA/1.41mA= 0.992

Is it correct brother? I understand all the equations and procedure but I doubt about the ques 2 answer. How to determine Ic from the curve ?
 

shteii01

Joined Feb 19, 2010
4,644
1) answer: base to collector dc curent gain
2) answer: Ic= 1.4mA (from the curve)
3) answer: beta dc= Ic/Ib = (1.4mA/10uA)= 140
4) answer: Ie=Ib+Ic
5) answer: Ie= Ib+Ic= (1.4mA+10uA)= 1.41mA
alpha= Ic/Ie= 1.4mA/1.41mA= 0.992

Is it correct brother? I understand all the equations and procedure but I doubt about the ques 2 answer. How to determine Ic from the curve ?
I am reading my text book. I think this is a problem where you use Load Line and Q-point.

Do you have any additional info? Vcc? Rc?
 

WBahn

Joined Mar 31, 2012
30,057
1) answer: base to collector dc curent gain
Correct, but arguably not clearly stated. Simpler and clearer might be that β=Ic/Ib under DC conditions.

2) answer: Ic= 1.4mA (from the curve)
3) answer: beta dc= Ic/Ib = (1.4mA/10uA)= 140
4) answer: Ie=Ib+Ic
5) answer: Ie= Ib+Ic= (1.4mA+10uA)= 1.41mA
alpha= Ic/Ie= 1.4mA/1.41mA= 0.992

Is it correct brother? I understand all the equations and procedure but I doubt about the ques 2 answer. How to determine Ic from the curve ?
These are all correct and you are reading the data off the graph just fine. Note that you didn't need the right hand curve at all. It's useful information, just not relevant to these particular questions.
 

WBahn

Joined Mar 31, 2012
30,057
I am reading my text book. I think this is a problem where you use Load Line and Q-point.

Do you have any additional info? Vcc? Rc?
But a load line involves two different components or circuits that each have to satisfy particular voltage-current characteristics. There's no second component here. You have a transistor with specified operating conditions, thus you only need the voltage-current characteristic for those operating conditions.
 
Top