difference between bipolar and mosfet

[Miles Harris]

On Mon, 10 Jan 2005 13:08:00 -0600, John Fields
<jfields@austininstruments.com> wrote:

Can you point to where I advocated the beta model for him to study?

Here's what you wrote earlier:

"The problem which arises here, I think, is that the change in base
voltage required to affect a change in collector current is so tiny
that it becomes easier to consider what happens on the other side of
the change in base voltage. That is, the collector-to emitter current
change due to the base-to-emitter current change."

Clear enough?

 

[John Fields]

On Mon, 10 Jan 2005 19:31:39 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Mon, 10 Jan 2005 12:47:04 -0600, John Fields
jfields@austininstruments.com> wrote:

If I didn't know the foundation was flawed, of course.

But you *do* know it's flawed, don't you - unlike the OP. You've
admitted as much to Kevin Aylward. And yet you're still prepared to
sell this flawed foundation to the OP!

---
What I told Kevin was that I had misstated something, not that I was
prepared to argue that the beta model was the be-all and end-all. If
you'd bother to go back and read my original post to the OP, instead
of playing your stupid posturing game, you might find that your entire
argument is baseless and, basically, noise.
---

Well, that really depends on what's meant by 'partially' and what's
meant by 'useful', wouldn't you agree?

Nitpicking isn't going to help the OP.

---
Never mind the newbie, the question was directed to you.
Do you agree or not?

It's a silly and pointless question so I'll decline, thanks.

---
Translation: Geez, if I fuck around with this guy I'm going to get my
head handed to me, so let's see if I can duck out by throwing a barb
and running away...

--
John Fields

 

[John Fields]

On Mon, 10 Jan 2005 22:16:50 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Mon, 10 Jan 2005 13:08:00 -0600, John Fields
jfields@austininstruments.com> wrote:

Can you point to where I advocated the beta model for him to study?

Here's what you wrote earlier:

"The problem which arises here, I think, is that the change in base
voltage required to affect a change in collector current is so tiny
that it becomes easier to consider what happens on the other side of
the change in base voltage. That is, the collector-to emitter current
change due to the base-to-emitter current change."

Clear enough?

---
Perfectly clear to me, and for a newbie who has to ask for the
difference between a BJT and a FET, an easy way to grasp that a tiny
change in base-to-emitter voltage will effect a change in
base-to-emitter current which will, in turn, cause a much larger
change in collector current.

ISTM that you think beta is so evil that, if you had your way, any
mention of beta and all Ic VS Ib curves would be totally eliminated
from all the data sheets in the world. It ain't gonna happen, so you
might as well get over it.

Or not. It makes very little difference to me, one way or the other.

--
John Fields

 

[John Fields]

On Tue, 11 Jan 2005 19:24:40 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Mon, 10 Jan 2005 18:08:01 -0600, John Fields
jfields@austininstruments.com> wrote:

Perfectly clear to me, and for a newbie who has to ask for the
difference between a BJT and a FET, an easy way to grasp that a tiny
change in base-to-emitter voltage will effect a change in
base-to-emitter current which will, in turn, cause a much larger
change in collector current.

That's the essence of the problem with your approach: easyness. Short
cuts are all very well provided they don't subvert fundamental
understanding along the way. Your 'easy' solution doesn't cut it in
this respect, I'm afraid.

---
What you're _really_ afraid of is that you'll be shown up for the
disingenuous piece of shit you really are, so you just keep on adding
fuel to the fire, buying time, waiting for what you think will be an
opportune moment to attack and "vindicate" yourself. Keep it up as
long as you like, I don't mind grinding you into the ground at all.
---

ISTM that you think beta is so evil that, if you had your way, any
mention of beta and all Ic VS Ib curves would be totally eliminated
from all the data sheets in the world. It ain't gonna happen, so you
might as well get over it.

I think you owe the OP one further explanation since you've sought to
rely on your 'easy' way out.

---
Wrong again. I don't owe the OP anything and the "reasoning" behind
why you think I do is irrelevant.
---

Kindly explain to him how, if he uses a
transistor with a beta listed as say 250 that he may in practice find
that his ratio of collector current to base current may be as much as
900:1?

---
Well, since you once again don't seem to have the answer, I'll be so
kind as to elucidate _your_ dumb ass, and if he wants to pick up on it
good for him.

If you take a look at a typical data sheet for a transistor,

http://www.fairchildsemi.com/ds/2N%2F2N4401.pdf

and learn how to read it, you will have answered your own question.
Better that than I should lead you astray by just telling you the
reason and letting you take the easy way out, no?

--
John Fields

 

[John Fields]

On Tue, 11 Jan 2005 19:24:39 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Mon, 10 Jan 2005 16:45:58 -0600, John Fields
jfields@austininstruments.com> wrote:

LOL! So what's good for the goose isn't good for the gander?

Where did I just read this: "Nitpicking isn't going to help the OP."?

It's not nitpicking, it's vitally important. Vb and Vbe are two
different things. Your "definition" should have referred to Vbe.
Similarly inexcusably sloppy was the reference to Vgs as Vg.

---
_My_ definition? Show me.
---

Unless otherwise stated, nitwit, that the emitter and the source are
the terminals to which the base voltage and gate voltage are
referenced is implicit.

So all my old textbooks that specifically refer to Vbe and Vgs are
being unnecessarily pedantic, then?

---
Certainly not. It's the job of textbooks to be as pedantic as possible
in order that some of the morons trying to glean meaning from them not
get confused and misinterpret what was being taught. Know what I
mean?
---

How are you then going to refer to
the 'absolute' values of gate voltage and base voltage (WRT ground)
without causing much confusion??

---
Unless otherwise stated, (and certainly for the purposes of this
discussion) the emitter and source are considered to be at ground,
i,e, 0V. When they're not, as would be the case with an emitter or a
source follower, then the schematic or text description would be
expected to make that clear.
---

Tell me how a newbie such as the OP or anyone else reading this group
to learn about the subject is supposed to *know* that sometimes some
idiots write Vg and Vb when they mean Vgs and Vbe?

---
Assholes like you will come along and offer their bile as
"corrections"?

Again, I'd be interested in having you cite examples where I wrote Vg
or Vs in this thread.
---

And personal insults are completely pointless, knob-head.

---
Yawnnn...

--
John Fields

 

[John Fields]

On Wed, 12 Jan 2005 08:06:17 GMT, "Kevin Aylward"

The rest of what you say here, is even more amazing.

---
Well, Kevin, it's only analogy...
---

The concept of transconductance is completely independent of whether
or not there is any control current.

But dig a little deeper and we find that all
the voltage across the base-emitter diode is doing is pumping charge
through the diode,

No. Vbe is setting an *electric field* that attempts to accelerate
charges from the emitter into the base region. This is truly 101
physics.

---
Yes, it is. I don't think anyone has said, yet, that it _isn't_ the
electric field which is making the electrons move, i.e. "pumping
charge", so It seems strange to me that you would think it has.
---

that _current_ being what causes the collector
current to flow.

NO! NO! NO!. Absolutly not. You are wrong. It is not the flow of charge
in the base that *causes* collecter current. This has already been
explained in many posts.

Charge flows because of:

F=q(E+vxB)

That is, excluding magnetic effects, it is *Electric Fields* that make
chages move. Period. The flow of charge, excluding magnetic effects,
cannot make other charge flow, other then by the change in electric
field that such flow might cause.

---
I said that the flow of charge between the emitter and base causes
charge to flow between the emitter and collector, and you say that's
wrong because the flow of charge between the emitter and base causes
charge to flow between the emitter and collector [because the flow of
charge between the emitter and base causes the electric field between
the emitter and collector to be changed to the point where charge can
flow between the emitter and collector.] Now where was I wrong,
exactly?
---

For the umpteenth time. Applying an *electric field* to the base emitter
injects carriers from the emitter into the base region. Once the
carriers are in the base region, they are attracted by the *electric
field* of the collector and are swept up (collected) by the collector
due to this *electric field*. Some of the emitter carriers just don't
make it, and are picked up via the base terminal. This base current is
an *effect* not a cause, and is incidental to the base emitter *electric
field* injecting carriers.

---
It doesn't matter how many times you say it, if it's not right it's
not right.

If it weren't for the base current there would be no collector
current, so it _is_ a cause, regardless of what's causing _it_ to
happen.
---

To repeat, it is not the *motion* of base charge that *causes* the
*motion* of collector/emitter charge. It is the electric field at Vbe
that causes both base current and collector/emitter current, as it is,
now get this 101 physics, *ELECTRIC FIELDS THAT MAKE CHARGES MOVE*. End
of story. Period.

---
I don't disagree with that.
---

---
If that's true, then a BJT isn't a transconductance device because the
collector current isn't a _direct_ consequence of the base-emitter
voltage, it's once removed since the _direct_ consequence of the
base-emitter voltage is the base-emitter current.

No. This shows that base current is an effect, of an electric field
cause.

---
Again, I don't disagree with that.
---

I am still amazed that after all these posts, you still don't understand
the basic operation of the bipolar transistor.

---
And I'm more than equally amazed that you don't seem to be able deal
with analogy.
---

....

And this is all wrong. I have already explained, a continuous resistance
would mean that the base is connected to that resistance, hence, no
transister action.

---
I don't know why you keep claiming that I said that the thing is a
slab of of either P or N type material, when what I said was that it
starts to _look_ like that between the collector and emitter when base
current starts flowing. Much like the region between the cathode and
the plate of a vacuum tube starts to look like a resistor when the
tube is conducting. Is there a resistor between the plate and the
cathode? No. Does it _look_ like there is? Yes.
---

Quite frankly, as noted above, you simply don't understand how a bipolar
transistor works. Read and understand the above. Its the way it is. I
can tell you that if you gave this description in an academic
semiconductor physics class, you would get a zero grade.

---
Perhaps, but since this is sci.electronics.basic, a rigorous treatment
of the matter is seldom apropos. In this instance, a simple reply to
the OP (which, BTW, you said you had no problem with) and some
analogies which you either misunderstood or decided to take issue with
for your own reasons seems to have led us up to where we now sit.

I, for one, no longer have the desire to continue with this
"discussion", so I'll excuse myself and bid you good day.

Thanks,

John

 

[Anthony Fremont]

"Bob Myers" <nospamplease@address.invalid> wrote in message
news:41e57c75$1@usenet01.boi.hp.com...

Sigh. If I might interject a couple of thoughts, just to hopefully
redirect this little p***ing contest into something more productive.

Could everyone please note the sign on the door, here? This is
sci.electronics.BASICS. While a number of us here are, in fact,
Professional Electrical Engineers of Long and Revered Standing
(at least, we have a diploma and someone actually pays us to do this
stuff), the questions here are more than likely going to come from
people who do NOT have such a background, are never going to
get into these phenomena down to the quantum-mechanics level,
and whose questions will be more than adequately satisfied by the
simple, "classical" explanations.

Are those explanations, in many cases, "wrong" in the sense that
they give what is to some degree a false or misleading understanding
of the fundamental physics underlying the operation of these
devices? Of course they are. But so what? If you're trying to
answer a question posed by someone who does not now and likely
never will care about his or her ability to derive the ideal diode
equation from basic principles, these simple explanations are very
likely still going to be the right choice. I strongly suspect that
just
about all of us who currently have some sort of "Engineer" title on
our business cards started with just the same level of understanding,
and
it didn't stop any of us from getting where we are today. As long
as it is made clear that the explanation being given IS a simplified
look at things, and that later on - IF they choose to go further -
they will learn more about what is really going on, I for one do not
see the harm in starting out at this level, as opposed to effectively
dumping a graduate-level solid-state physics texts in their laps and
saying "there you go." That sort of approach, IMHO, does NOT
serve the purpose of this newsgroup.

All too often, we seem to have requests for such basic information
posted by someone who is quite clearly an amateur/hobbyist, followed
by a response by someone apparently interested primarily in
demonstrating their own command of the intricacies of the topic
in question, rather than actually saying something that the original
poster would find helpful. I would like to respectfully suggest that
such an approach is, to say the very least, idiotic.

We now return you to your irregularly-scheduled chest-beating...

Hurray Bob! ) I started to write something along these lines, but
couldn't make it sound as nice as you just have. I think it's important
to also note that everyone's model is wrong in the strictest sense of
definition of correctness. They are all just models, and like all
models, they serve to be a "reasonable" facsimile of the real and
absolute truth; whatever that may be. They are not perfect or they
wouldn't be called models. I'm reasonably sure that there are people
that could come in and make a mockery of every model that has been
presented here by demonstrating their shortcomings and failures. I
suspect some of those people are actually present here reading this, but
not wishing to add fuel to the fire.

 

[Robert Monsen]

Kevin Aylward wrote:
<snip arguments for and against>

The fact that current through a bipolar transistor and a diode are
described by basically the same equation points to the fact that a
bipolar transistor is really just a diode, in which many or most of the
electrons that would normally escape through the base are diverted to
the collector by the geometry and chemistry of the device and voltage on
the collector. Since a diode is clearly a voltage controlled device, it
is clear that the voltage across the PN junction of the base to emitter
that causes electron flow.

However, saying that current through the base has nothing to do with
this is just wrong. Because of the fact that a diode is involved, the
only way to keep the voltage of the base up is to pull electrons out of
it through the base lead. The ratio of electrons out the base lead to
electrons out the collector is 'fairly' stable, enough to be printed in
datasheets as the famous hfe or beta parameter.

Because of this, the base current is yet another feature of the bipolar
transistor that can be used to roughly predict the collector current,
and thus to design circuits with. It is also easier to use, in my
opinion, owing to the fact that the relationship between base and
collector current is generally linear, within certain ranges.

On the other hand, in my experience, the voltage to current equation is
far more less use, since Is is not generally published in datasheets,
and is severely temperature dependent to boot (just like beta).
Predicting the current through the collector of a a 2N3904, given a base
voltage, is practically impossible. Predicting the current through a
2N3904 using beta is simple, if somewhat imprecise. By guessing a beta
of 100, one can easily see that 10uA through the base will give about
1mA through the collector.

Both beta and EM have their place in one's toolkit. Why toss out tools
that can be useful?

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.

 

[John Fields]

On Wed, 12 Jan 2005 12:35:45 -0700, "Bob Myers"
<nospamplease@address.invalid> wrote:

Sigh. If I might interject a couple of thoughts, just to hopefully
redirect this little p***ing contest into something more productive.

Could everyone please note the sign on the door, here? This is
sci.electronics.BASICS. While a number of us here are, in fact,
Professional Electrical Engineers of Long and Revered Standing
(at least, we have a diploma and someone actually pays us to do this
stuff), the questions here are more than likely going to come from
people who do NOT have such a background, are never going to
get into these phenomena down to the quantum-mechanics level,
and whose questions will be more than adequately satisfied by the
simple, "classical" explanations.

Are those explanations, in many cases, "wrong" in the sense that
they give what is to some degree a false or misleading understanding
of the fundamental physics underlying the operation of these
devices? Of course they are. But so what? If you're trying to
answer a question posed by someone who does not now and likely
never will care about his or her ability to derive the ideal diode
equation from basic principles, these simple explanations are very
likely still going to be the right choice. I strongly suspect that just
about all of us who currently have some sort of "Engineer" title on
our business cards started with just the same level of understanding, and
it didn't stop any of us from getting where we are today. As long
as it is made clear that the explanation being given IS a simplified
look at things, and that later on - IF they choose to go further -
they will learn more about what is really going on, I for one do not
see the harm in starting out at this level, as opposed to effectively
dumping a graduate-level solid-state physics texts in their laps and
saying "there you go." That sort of approach, IMHO, does NOT
serve the purpose of this newsgroup.

All too often, we seem to have requests for such basic information
posted by someone who is quite clearly an amateur/hobbyist, followed
by a response by someone apparently interested primarily in
demonstrating their own command of the intricacies of the topic
in question, rather than actually saying something that the original
poster would find helpful. I would like to respectfully suggest that
such an approach is, to say the very least, idiotic.

We now return you to your irregularly-scheduled chest-beating...

---
Decent!

--
John Fields

 

[Miles Harris]

On Wed, 12 Jan 2005 11:41:25 -0600, John Fields
<jfields@austininstruments.com> wrote:

I, for one, no longer have the desire to continue with this
"discussion", so I'll excuse myself and bid you good day.

Translation: "My ass can't take no more whuppin' so I'm outa here!"

 

[Miles Harris]

On Wed, 12 Jan 2005 11:58:08 -0600, John Fields
<jfields@austininstruments.com> wrote:

Beta is simply collector current divided by base current. At the OP's
current <G> level of understanding, that's all he needs to know, so
why would it take you longer than a minute to come up with that?

You've pre-empted my considered view on the matter (see my posting of
earlier today further up the thread).

 

[John Fields]

On Thu, 13 Jan 2005 10:38:26 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Wed, 12 Jan 2005 11:58:08 -0600, John Fields
jfields@austininstruments.com> wrote:

Beta is simply collector current divided by base current. At the OP's
current <G> level of understanding, that's all he needs to know, so
why would it take you longer than a minute to come up with that?

You've pre-empted my considered view on the matter (see my posting of
earlier today further up the thread).

---
I should go on a wild goose chase at your insistence? Forget it. If
you have something to say, include it in the current post.

--
John Fields

 

[Jamie]

John Fields wrote:

On Thu, 13 Jan 2005 08:34:10 -0600, John Fields
jfields@austininstruments.com> wrote:


On Thu, 13 Jan 2005 10:38:26 GMT, Miles Harris <mazzer@yahoo.com
wrote:


On Wed, 12 Jan 2005 11:58:08 -0600, John Fields
jfields@austininstruments.com> wrote:


Beta is simply collector current divided by base current. At the OP's
current <G> level of understanding, that's all he needs to know, so
why would it take you longer than a minute to come up with that?

You've pre-empted my considered view on the matter (see my posting of
earlier today further up the thread).

---
I should go on a wild goose chase at your insistence? Forget it. If
you have something to say, include it in the current post.


---
That was unnecessarily nasty. I apologize.

thats ok, i am enjoying it!

 

[Miles Harris]

On Thu, 13 Jan 2005 08:28:08 -0600, John Fields
<jfields@austininstruments.com> wrote:

Then why did you snip it? Bandwidth is cheap.

Storage, OTOH, isn't as cheap and we can all snip a lot more savagely
to make life easier for Google and other archivists.

I've been posting to Usenet for many years, but normally use
X-no-archive or my nickname or whatever. Some of the views I put
forward on political matters are sadly not regarded as acceptable
these days, so when needs must....
---
So on top of it all you're a sneak? What a surprise!

Sadly, pointing out the truth about certain things in this world is no
longer acceptable. Political-correctness and such like. It's slowly
getting worse, too. For some factual historical views one can even
risk imprisonment and have one's carreer and livelihood destroyed. The
views are too important to hide, so they have to be disseminated by
stealth. It requires that certain precautions be taken. A shameful
situation, I grant you.

miles
END QUOTE

which seems to belie your claim that you're an electrical engineer
with 35 years of experience.

Really? So what is it you're taking issue with? Taken as a
generalization for most silicon diodes I can't see real problem with
it.

---
The fact that you can't see that there's a problem with it is
precisely the problem. Tell me, did you help desigh the Tacoma
Narrows bridge?

As I recall (dimly) high winds cutting across the bridge built up a
series of increasingly violent osicallations, resulting in its total
destruction. Are you trying to say a diode would oscillate itself to
destruction? I've noticed you're not very good with analogies so I'm
afraid whatever your beef is, you're gonna have to spell it out in
plain English....

I'm not suggesting anything of the kind. What I'm _stating_ is that
you made a mistake and then tried to pretend you didn't by doing that
little sidestep shuffle.

Sue you? Fuck you.

No idea what you're talking about, I'm afraid, Old Fruit.

 

[Miles Harris]

On Thu, 13 Jan 2005 08:14:21 -0600, John Fields
<jfields@austininstruments.com> wrote:

Actually, it's "What's the point of whipping a dead horse?" (Not you,
Kevin, the subject material.

Well it appears that Kevin has straightened out your misconceptions
about how a transistor works and set you on the right road to further
studies on a firm foundation. I suppose it's too much to expect you to
show him an ounce of gratitude for his (considerable) time and
trouble. :-(

 

[Miles Harris]

On Thu, 13 Jan 2005 09:42:52 -0600, John Fields
<jfields@austininstruments.com> wrote:

That was unnecessarily nasty. I apologize.

No problem.
Being a seasoned Usenetter of some 13 years standing, it takes a bit
more than mild sarchasm to give me a bad day ;->
Work hard on your studies, Junior. Nothing comes easy in this life
except to the very fortunate.

 

[Miles Harris]

On Thu, 13 Jan 2005 13:05:07 -0800, Jamie
<jamie_5_not_valid_after_5_Please@charter.net> wrote:

thats ok, i am enjoying it!

Put it out of your mind as a pointless distraction, sonny and get
stuck back into your textbooks. Head down and study, study, study is
the only realistic way to success.
HTH

 

[Bob Myers]

"John Fields" <jfields@austininstruments.com> wrote in message
news:km2eu09sm9uccpeitrviqfmddtf783cq3k@4ax.com...
-

Waking up in the morning knowing you've got email waiting does it for
you, I expect Anyway, what's 'sarchasm'? Sounds like something you
fall into when you can't figure out the insult...

No, a sarchasm is where they tossed all those poor unfortunate
chickens in China and Hong Kong a couple of years back....

Sorry to interrupt this little lovefest here...I'll go back to my
knitting now....

Bob M.

 

[John Fields]

On Fri, 14 Jan 2005 11:58:18 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Thu, 13 Jan 2005 17:55:54 -0600, John Fields
jfields@austininstruments.com> wrote:

Nothing of the kind. Kevin and I have been at loggerheads with each
other more than once in the past, and he knows that I have a great
deal of respect and affection for him, so your disingenuous
"refereeing" falls on deaf ears. However, _your_ sickening pomposity
has been noted.

I can only apologize.

---
Apology accepted.
---

Sadly, It's all too easy to fall into the trap of talking down to
one's inferiors.

---
You're right. I'll try not to in the future.
---

Especially when the ability-gulf is so wide.

---
Yes, I know. That's what makes it so easy to demean you.
---

I don't wish to appear patronizing, but in your case, it's
unavoidable.

---
As I said, I'll try not to in the future.


--
John Fields

 

[Miles Harris]

On Wed, 12 Jan 2005 08:06:17 GMT, "Kevin Aylward"
<salesEXTRACT@anasoft.co.uk> wrote:

For the umpteenth time. Applying an *electric field* to the base emitter
injects carriers from the emitter into the base region. Once the
carriers are in the base region, they are attracted by the *electric
field* of the collector and are swept up (collected) by the collector
due to this *electric field*. Some of the emitter carriers just don't
make it, and are picked up via the base terminal. This base current is
an *effect* not a cause, and is incidental to the base emitter *electric
field* injecting carriers.

To repeat, it is not the *motion* of base charge that *causes* the
*motion* of collector/emitter charge. It is the electric field at Vbe
that causes both base current and collector/emitter current, as it is,
now get this 101 physics, *ELECTRIC FIELDS THAT MAKE CHARGES MOVE*. End
of story. Period.

Nicely put.
I doubt it'll be the end of the story, though. I suspect John Fields
may be a troll. No rational person could conceivably be so obtuse.