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How to know a transistor is carrying out its function ?

by Outrageous
Tags: carrying, function, transistor
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Outrageous
#19
Nov24-12, 05:31 PM
P: 375
Quote Quote by Outrageous View Post
Given Vbe=0.7V
Vb=0.7V
Ve=0
Vc=5.0V
Ib=0.45μA
Ic=100Ib
There is voltage supplied
Then change R1 to Vb
R2 to Vc
Will it look okay?
Studiot
#20
Nov24-12, 05:36 PM
P: 5,462
Will it look okay?
No.

Look again at my circuit configuration and compare it with yours.

Where is the base resistor connected in each?
Outrageous
#21
Nov24-12, 06:06 PM
P: 375
My base resistor is connected to the emitter, yours is connected to the committer.

Mine is common emitter, I don't know yours

This will affect voltage supplied to base and committer ?
Studiot
#22
Nov24-12, 06:14 PM
P: 5,462
Yes indeed your base resistor as connected will have no voltage across it.

The bias resistors do not determine whether the configuration is common emitter or common collector.
That is determined by the terminal that is common between input and output.
Jony130
#23
Nov24-12, 06:21 PM
P: 409
From your post we can tell one thing. You simply don't understand how NPN transistor work from engineers point of view.
How can any current to flow if the base is connect (short) with emitter?
Outrageous
#24
Nov24-12, 07:14 PM
P: 375
Quote Quote by Studiot View Post
Yes indeed your base resistor as connected will have no voltage across it.

The bias resistors do not determine whether the configuration is common emitter or common collector.
That is determined by the terminal that is common between input and output.
Quote Quote by Jony130 View Post
From your post we can tell one thing. You simply don't understand how NPN transistor work from engineers point of view.
How can any current to flow if the base is connect (short) with emitter?
So from my diagram, the current will not flow through base-emitter even though I connect Vb=+0.7V , instead , the current will straight flow to the earth, correct?
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Studiot
#25
Nov24-12, 07:29 PM
P: 5,462

So from my diagram, the current will not flow through base-emitter even though I connect Vb=+0.7V , instead , the current will straight flow to the earth, correct?

I seriously recommend that your learning process would be much enhanced and more efficient if you paid heed to what others who have gone before are telling you as well as simply asking question after question, many of which suggest you did not take notice of a previous answer.

The circuit you have just posted will simply burn out the transistor.

I am happy to discuss the perfectly satisfactory circuit I posted in post#4 , which has much to tell us, but this is already post #25 of this thread which seems to be going nowhere.
Outrageous
#26
Nov25-12, 03:27 AM
P: 375
I asked because I still don't understand . So I must follow your diagram only can get true diagram? I don't know why resistor must connected between base and collector, why not base and emitter.
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jim hardy
#27
Nov25-12, 09:47 AM
Sci Advisor
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Two questions re sketch in post #9:

1. That line that connects R1 to R2 crosses the emitter line - is it connected there, or is it connected to a source of +5 voltage ? If the former, everything is tied to 0volts and those voltages are impossible.

2 What does teacher have in mind when (s)he says "operating"?
If that R1-R2 line is connected to positive 5V and the voltages are indeed what you posted,
the transistor is in, or very near, saturation, so it won't have a lot of AC voltage gain.
To an audio person that would appear not operating, but to a logic circuit person it's doing just fine.

I hope i'm on topic here - i tend to confuse easily so if off just ignore.

old jim
sophiecentaur
#28
Nov25-12, 11:37 AM
Sci Advisor
Thanks
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P: 12,130
Quote Quote by Outrageous View Post
I asked because I still don't understand . So I must follow your diagram only can get true diagram? I don't know why resistor must connected between base and collector, why not base and emitter.
Just think What would your resistor achieve - it would merely be in parallel with the junction? It would not supply any base current and would merely lower the input resistance of the amplifier.
I think you should take to heart Studiot's earlier comment. Question and answer, just on your terms, will not achieve very much for you and it will just irritate people who know they are giving you good information. Just consider that you may be wrong about some things and Read Around to find things out. You have such a luxury these days, in the form of the WWW. Why not use it constructively and make a proper effort.
Outrageous
#29
Nov25-12, 06:08 PM
P: 375
I am sorry for being so lazy to find out on my own.

I think this is the answer for this thread , I will try to read more first only ask.
Quote Quote by jim hardy View Post
2 What does teacher have in mind when (s)he says "operating"?
If that R1-R2 line is connected to positive 5V and the voltages are indeed what you posted,
the transistor is in, or very near, saturation, so it won't have a lot of AC voltage gain.
To an audio person that would appear not operating, but to a logic circuit person it's doing just fine.
Thanks :)
Studiot
#30
Nov26-12, 02:25 AM
P: 5,462
Please take note that the 'off' condition is a valid operating condition for a transistor.

That is if Vce = 0.1 volts or 0 volts then a valid condition would be that a perfect transistor is not passing current.

Sometimes we want to switch th transistor off.
There is currently (pun intended) another thread here where a poster is trying to achieve exactly that with a light switch.


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