transistors

[Sunil]

hi.....can anyone define input and output impedence of a transistor??
and how do you find it out experimentally??

 

[Eeyore]

hi.....can anyone define input and output impedence of a transistor??

It depends on the circuit it's operated in. If you're referring to the device
itself alone, those parameters will vary with collector current.

and how do you find it out experimentally??

By measurement !

Now, maybe you can us about the reason behind your question.

Graham

 

[Sunil]

my professor measured it using the ratio between Rin and Rs (internal
resistance)....i kinda dint understand that...can u xplain me this
method??

 

[Rich Grise]

my professor measured it using the ratio between Rin and Rs (internal
resistance)....i kinda dint understand that...can u xplain me this
method??

Why can't you go to the prof., and say, "I still don't get this -
can you explain it to me again, in a form I can understand?"

Good Luck!
Rich

 

[Eeyore]

my professor measured it using the ratio between Rin and Rs (internal
resistance)....i kinda dint understand that...can u xplain me this
method??

Frankly, if you want my precise opinion, most 'professors' haven't the tiniest
clue about real world electronics and would be better employed cleaning the
lavatories than teaching kids who actually want to learn something of value.

I have experienced the same frustration myself (at UCL London would you believe
?) but it was solved by a supposedly 'inferior' teacher at a mere polytechnic
who wrote an excellent series of articles on precisely this subject in the
reknowned UK magazine "Wireless World". He swept away the usual professor's
stuffy nonsense and voodoo and replaced it with simple to understand practical
science.

Now, I don't have a reference for those articles I'm afraid but it seems to me
that maybe it's time to find out which issues they were in. The approximate time
frame for this is the mid 1970s.

Graham

 

[Eeyore]

Why can't you go to the prof., and say, "I still don't get this -
can you explain it to me again, in a form I can understand?"

I went to the Prof (age 18) and said (something along the lines of to the best
of my memory) why are you using Y parameters when no damn * (OK I didn't say
"damn") semiconductor manufacturer publishes any such damn * thing and I think
he was mostly embarassed that a student was probably better informed about
current practice than he was.

His answer when I suggested that H parameters might be more useful was IIRC
"that's another way you can do it". DUH !

What a useless piece of trash ! I had 2 very good friends on the course who both
admitted at the end of the first year "I still don't understand what a
transistor does". I did and I hadn't learnt it at UCL and that's why I left.

Graham

 

[bg]

Sunil wrote in message

hi.....can anyone define input and output impedence of a transistor??
and how do you find it out experimentally??

Connect a battery and a resistor in series with a base emitter junction.
Measure the voltage across the resistor and the voltage across the BE
junction. From ohms law you can figure out the current flowing into the
junction and the resistance of the junction. The BE junction normally
operates somewhere between .6 to .7 volts, so keep the BE voltage within
that range for realistic values. Over that range of BE voltages , you should
see that the resistance of the junction changes. If it didn't change, it
would be a simple matter of measuring it with an ohmeter.
This is something that you should have done and understood using dry cells
and light bulbs long before getting into transistors.

 

[Eeyore]

Sunil wrote in message


Connect a battery and a resistor in series with a base emitter junction.
Measure the voltage across the resistor and the voltage across the BE
junction. From ohms law you can figure out the current flowing into the
junction and the resistance of the junction.

You just measured a DIODE not a transistor.

Please don't flaunt your ignorance in this way.

Graham

 

[bg]

You just measured a DIODE not a transistor.

Please don't flaunt your ignorance in this way.

Graham

Ok so we measured h and not Bh, but the flaunting is not negotiable.
thanks

 

[Jamie]

Sunil wrote:




It depends on the circuit it's operated in. If you're referring to the device
itself alone, those parameters will vary with collector current.





By measurement !

Now, maybe you can us about the reason behind your question.

Graham

Now you're starting to sound like one of the brothers,
here in the states!.
Keep it up, you'll be wearing an American patch very soon!

 

[Jamie]

Rich Grise wrote:




I went to the Prof (age 18) and said (something along the lines of to the best
of my memory) why are you using Y parameters when no damn * (OK I didn't say
"damn") semiconductor manufacturer publishes any such damn * thing and I think
he was mostly embarassed that a student was probably better informed about
current practice than he was.

His answer when I suggested that H parameters might be more useful was IIRC
"that's another way you can do it". DUH !

What a useless piece of trash ! I had 2 very good friends on the course who both
admitted at the end of the first year "I still don't understand what a
transistor does". I did and I hadn't learnt it at UCL and that's why I left.

Graham

No comment.. How ever, I do admire your truthfulness.

There is some good there, just damn hard to find.

 

[Jamie]

Ok so we measured h and not Bh, but the flaunting is not negotiable.
thanks

Pay no mind to Mr Ham.. He can be as rude as he can be ignorant.

Frankly, I don't understand the instructor placing a question in suck
an awkward manner? In any case. Your idea of applying current in the base,
assuming the emitter is at common, is just one step less than that of
the final process of measuring the current from source to C.(collector).

This would then give you the current gain ratio. found in reference of
Hfe, also found in text as Beta.
Now most of us know, that figure is not absolute due to the nature of
bipolar transistors.

The above assumes bipolar, since, that is most likely what they teach
first in school.

 

[Eeyore]

Pay no mind to Mr Ham.. He can be as rude as he can be ignorant.

Whereas you can be relied upon to be ignorant and WRONG about everything.

Graham

 

[Eeyore]

Now you're starting to sound like one of the brothers,
here in the states!.

"Brothers" ? I thought that was a reference to 'black' people.

Keep it up, you'll be wearing an American patch very soon!

Not everything American is a bad thing !

Graham

 

[Noway2]

hi.....can anyone define input and output impedence of a transistor??
and how do you find it out experimentally??

The book, "The Art of Electronics" does an excellent job of explaining
how transistors work AND I might add, how to use them in practical
applications.

 

[bg]

Jamie wrote in message ...

Pay no mind to Mr Ham.. He can be as rude as he can be ignorant.

Frankly, I don't understand the instructor placing a question in suck
an awkward manner? In any case. Your idea of applying current in the base,
assuming the emitter is at common, is just one step less than that of
the final process of measuring the current from source to C.(collector).

This would then give you the current gain ratio. found in reference of
Hfe, also found in text as Beta.
Now most of us know, that figure is not absolute due to the nature of
bipolar transistors.

The above assumes bipolar, since, that is most likely what they teach
first in school.

Graham is right. I gave a wrong answere.Unlike some people, I don't have a
problem with that.
bg

 

[Eeyore]

Jamie wrote in message ...
Graham is right. I gave a wrong answere.Unlike some people, I don't have a
problem with that.
bg

I apologise for my bluntness.

Graham

 

[Jamie]

Jamie wrote:




"Brothers" ? I thought that was a reference to 'black' people.

Well, you may think so how ever, over here black people call
white people brothers. That does stir up the pot a bit!

Not everything American is a bad thing !

Graham

You change your mind like most people change their underwear.

Like I said, most people. That may exclude you.!

 

[Jamie]

Jamie wrote in message ...

Graham is right. I gave a wrong answere.Unlike some people, I don't have a
problem with that.
bg

I understand that how ever, the procedure you describe even though
wasn't correct, was just incomplete of what should have been done in
my opinion.

Many people make mistakes how ever, I find that many of them are not
due to some one not knowing. They are due to oversight of an error made
while thinking ahead to fast.

It's like taking a test.

A person sets up a pool of questions. This person may just be
taking references out of a book and only expecting 1 answer..

In many cases, the person preparing the test is not really savvy
(hands on) in the field. So in his mind, it's straight forward.

Along comes the victim taking the test.

Now, if this victim studied the same reference materials, that of the
question pool. He's going to know only 1 answer how ever, some one that
has already been around the barn a few times is going to look at that
question and come up with multiple scenarios. which in that case, starts
a flame war here.

Nothing directed to you, just an observation i've made here lately.

There are a couple here that change their minds like the wind in New
England to suite their daily needs.

Oh well.

Have a great day,.

 

[Jamie]

bg wrote:




I apologise for my bluntness.

Graham

That's today.