But you haven't measured it?

You said you were asked to show that the hfe in the power transistors was less than in the small signal transistors. Well, doesn't it seem like the first step in showing that is to measure the hfe in the power transistor and to measure the hfe in the small signal transistor?

 

Isn't this done for constant Ib increments with sweeping Vce vs Ic
Is projecting these slopes , what determines the negative Va or Early Effect apparent threshold for an NPN?
I have not done this before.

Thus Vbe , hFE etc is irrelevant, just the relative levels of Ic, Vce in comparing devices.

 

But you haven't measured it?

You said you were asked to show that the hfe in the power transistors was less than in the small signal transistors. Well, doesn't it seem like the first step in showing that is to measure the hfe in the power transistor and to measure the hfe in the small signal transistor?

Well, about hFE, there is nothing asked in the report. But my teacher talked to me yesterday about that. Not that that is asked in the report. So If I can tell something about hFE, the better...

But I know that hFE for 2N2222 is between 100 and 300 from the datasheets and that Q2N3055 is between 20 and 70.

Isn't this done for constant Ib increments with sweeping Vce vs Ic
Is projecting these slopes , what determines the negative Va or Early Effect apparent threshold for an NPN?
I have not done this before.

Thus Vbe , hFE etc is irrelevant, just the relative levels of Ic, Vce in comparing devices.

View attachment 83691

Yes I know about that. But teacher's questions are about different matters, so we need to cover some of the key aspects of transistors... That's why we are talking about all this and not only about hFE or only about Early Effect, and so on!

 

And you have problem with ?? Because I already try to tell you that the power transistor has a smaller Vbe than small-signal transistor For Ic smaller than 100mA. Why? Because power transistor has a large junction area.

 

And you have problem with ?? Because I already try to tell you that the power transistor has a smaller Vbe than small-signal transistor For Ic smaller than 100mA. Why? Because power transistor has a large junction area.

But in my last plots I could not verify that Jony130... That is the point I'm trying to understand to finish this question!

 

Simple try to compare Vbe values for a given Ib current for 2N2222 Vs 2N3055.
For example look here


And we can see that for Ib = 100μA we have
Vbe =740mV for 2N2222 and Vbe = 330mV for 2N3055

 

But in my last plots I could not verify that Jony130... That is the point I'm trying to understand to finish this question!

But you DID verify this! Look at what you wrote in Post #3:

I have noticed that in 2N2222, this plot gives the idea that in B-E junction we have a regular diode (Vγ≈0.7V) and and in 2N3055 this same voltage says ≈0.36V. I was wondering if this (or all) power bjt's are built with a schottky diode at the B-E junction.

So you had the same Ib and in the small signal transistor you got about 0.7V and in the power transistor you got about half that.

 

But you DID verify this! Look at what you wrote in Post #3:

So you had the same Ib and in the small signal transistor you got about 0.7V and in the power transistor you got about half that.

I did verify that but it was with another base current. But I think I got the point. This Vbe is lower for power transistors for the same given base current. However this Vbe can be different depending on the range of base current and collector current, right?

 

And you have problem with ?? Because I already try to tell you that the power transistor has a smaller Vbe than small-signal transistor For Ic smaller than 100mA. Why? Because power transistor has a large junction area.

That junction you are talking about is B-E, right? Or what is it?

 

I did verify that but it was with another base current. But I think I got the point. This Vbe is lower for power transistors for the same given base current. However this Vbe can be different depending on the range of base current and collector current, right?

For most silicon BJT transistors near room temperature, a change in collector (or base) current of a factor of ten results in a change in Vbe of about 60mV.

 

Ok, I ended up including one additional simulation, meaning that I used a simulation with base current going from 0 A up to 400 mA to show how at this current rates, the behaviour can be different from other base current ratings. Then I used another simulation using the same values I used in 2N2222 to compare their Vbe for the same base current at a given collector current. I think this way I can show a bit more about both transistors and their differences!