Hello everyone, I’m revising BJTs in a common-base configuration and I’ve calculated and simulated this example found online some time ago (I can’t remember where):
WRONG:


UPDATE:


I used beta = 200, so I modified the ‘BF’ factor of an existing BJT.

Does this circuit make sense?
Can we call it a common-base circuit? … is the input above Re missing? I don’t understand the purpose of Ve

 

No. Your circuit makes no sense. Vout will always be 12 V.
You need to show Vin and Vout.
Ve is needed if you want bipolar operation.
beta = 200 is somewhat high. Use beta = 100.

 

No. Your circuit makes no sense. Vout will always be 12 V.
You need to show Vin and Vout.
Ve is needed if you want bipolar operation.
beta = 200 is somewhat high. Use beta = 100.

Sorry, I’ve got a bit confused!
Vout obviously goes below 4.7k… I’ve updated the main post

 

No. Your circuit makes no sense. Vout will always be 12 V.
You need to show Vin and Vout.
Ve is needed if you want bipolar operation.
beta = 200 is somewhat high. Use beta = 100.

I agree that it doesn’t make sense; I just wanted to be sure.
It was probably just there to help with the calculations, as it was one of many exercises

Why is beta=200 considered high?

I wonder if it can be called a common base if Vi is missing… am I right?

 

Beta is not constant and depends on collector current.
Some transistor spec sheets will show beta greater than 300.
A circuit design should not depend on any specific value of beta.
beta = 100 is a better starting point. If the exercise states a value for beta then use that value.

If Vi is missing, then the circuit functions as some kind of voltage source.

 

hi Andrew,
A couple of errors on your asc circuit drawing.
To shrink the length of the model text, use keys Ctrl and M the add the leading '+' sign
As already pointed out actual circuit needs a redesign.
E

 

hi Andrew,
A couple of errors on your asc circuit drawing.
To shrink the length of the model text, use keys Ctrl and M the add the leading '+' sign
As already pointed out actual circuit needs a redesign.
E
View attachment 371252

thanks !!