difference between bipolar and mosfet

[Kevin Aylward]

John Fields wrote:

On Tue, 11 Jan 2005 07:39:01 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:

John Fields wrote:
On Mon, 10 Jan 2005 08:19:50 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:

No. They are a transconductance device because applying a voltage
across the base emitter junction injects carriers from the emitter
to the base *region*. This charge essentially *all* flows out of
the collecter, not the base terminal.

---
Not no.

Yes no.

---
Not yes no
---


From:

http://searchsmallbizit.techtarget.com/sDefinition/0,,sid44_gci214200,00.html

"Transconductance is an expression of the performance of a bipolar
transistor or field-effect transistor (FET). In general, the larger
the transconductance figure for a device, the greater the gain
(amplification) it is capable of delivering, when all other factors
are held constant.

{etc sniped.}

I have no basic problems with this quote, its all good stuff.
However, it has absolutely nothing to do with my point. It certainly
has no relevance as to why a transistor is a transconductance
*device*.

"Transconductance" in the above is a pure and general mathematically
technique used to model a physical phenomena. It doesn't care
whether or not the phenomena is actually physically current
controlled by a voltage. My description that a bipolar is a
"transconductance device" is statement of its actual physics.

---

No, it's not. A true transconductance device is one in which no
current is required into the control electrode.

No. I have to say here, this is absolute nonsense. I cant believe I am
actually reading this.

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

The grid of a toob in
the region where no grid current is drawn more nearly approximates a
"true transconductance" device.

Sorry, mate, this is only *your* personal concept of a "true
transconductance" device. Somewhere you have picked up an erroneous view
without even thinking about it. The *only* requirement for a
transconductance is the output current is a direct function of a control
voltage. Any current at the control terminal is simply irrelevant.

Your admission that base current must
exist before collector current can exist makes the BJT a
"transresistance device",

No it don't. This is getting daft. The bipolar transistor is, to first
order, a voltage controlled current source. It is therefore a
transconductance device. Period.

since the base current is inseparable from
the base-to-emitter voltage when the BJT is operating.

Ho hummm...

BTW, if it's singular, it's "phenomenon".
---

that charge changing
the electrical properties of the base material to more closely
approximate those of the collector and emitter. That is, when
charge is injected into the base-to-emitter diode of a PNP
transistor, the "N" type base material becomes more and more "P"
like as more and more current is forced through it, with the
result that the transistor starts looking more and more like a
single piece of low-resistance "P" type material as more and more
current flows through the base-to-emitter junction.

This is not an accurate description of the bipolar transistor. This
description is more relevant to operation of the mosfet. The npn
junction simply does not act like a slap of N type. If it did, base
current would be huge.

---
yes, were it not for the current limiting resistance external to the
base the base current could become huge.

For a given emitter current, the base current will always be a small
fraction due to transistor action. If the npn junction were just a
slab of n type then there would be a direct connection from base to
emitter resulting in larger current. You would just have resisters
connecting base emitter and collector all together and therefore no
hfe.

---
But, in fact, it _isn't_ a slab of N type material,

That's what I am claiming, you are claiming otherwise.

it's a carefully
arranged sandwich made to become more or less resistive by changing
the electrical characteristics of the filling.
---

Therefore you are claiming by this that it *is* a slab of resistance.

---
Hardly. Here this newbie asks "What makes a BJT different from a
FET?" and you reply "If you put a voltage across the base and
emitter terminals of a BJT current will flow between the collector
and emitter, while if you put a voltage across the gate and source
terminals of a FET current will flow between the drain and the
source." So, while your description may be true, its utter
simplicity leads the newb to think they're the same same thing with
differently named terminals.

The above statement is with regard to the control of the collector
current only. It obviously needs a statement that "base current must
exist in real device".

---
Then it's not quite as simple as "Vbe controls the collector/emitter
current.", is it?

It is, if we neglect rbb'. The fact that a source has to supply current
is irrelevant.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[John Fields]

On Tue, 11 Jan 2005 19:57:25 GMT, "Kevin Aylward"
<salesEXTRACT@anasoft.co.uk> wrote:

John Fields wrote:
On Tue, 11 Jan 2005 07:39:01 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:

John Fields wrote:
On Mon, 10 Jan 2005 08:19:50 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:

No. They are a transconductance device because applying a voltage
across the base emitter junction injects carriers from the emitter
to the base *region*. This charge essentially *all* flows out of
the collecter, not the base terminal.

---
Not no.

Yes no.

---
Not yes no
---


From:

http://searchsmallbizit.techtarget.com/sDefinition/0,,sid44_gci214200,00.html

"Transconductance is an expression of the performance of a bipolar
transistor or field-effect transistor (FET). In general, the larger
the transconductance figure for a device, the greater the gain
(amplification) it is capable of delivering, when all other factors
are held constant.

{etc sniped.}

I have no basic problems with this quote, its all good stuff.
However, it has absolutely nothing to do with my point. It certainly
has no relevance as to why a transistor is a transconductance
*device*.

"Transconductance" in the above is a pure and general mathematically
technique used to model a physical phenomena. It doesn't care
whether or not the phenomena is actually physically current
controlled by a voltage. My description that a bipolar is a
"transconductance device" is statement of its actual physics.

---

No, it's not. A true transconductance device is one in which no
current is required into the control electrode.


No. I have to say here, this is absolute nonsense. I cant believe I am
actually reading this.

---
Believe it!-)
---

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

---
Granted, but what you said you wanted to talk about wasn't the concept
of transconductance, it was that the "actual physics" of a BJT made it
a transconductance device. That being the case, what's nonsensical is
that almost anything can be called a transconductance device, so just
calling a BJT a transconductance device doesn't really say anything
about the physics behind it. Consider a simple potentiometer on the
bridge of a ship which is used to control the ship's speed. Is what's
being used to turn the screw a transconductance device? Sure. Does
it tell us anything about what's between the pot and the screw? No.
Same thing with a BJT. 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, that _current_ being what causes the collector
current to flow.
---

The grid of a toob in
the region where no grid current is drawn more nearly approximates a
"true transconductance" device.

Sorry, mate, this is only *your* personal concept of a "true
transconductance" device. Somewhere you have picked up an erroneous view
without even thinking about it. The *only* requirement for a
transconductance is the output current is a direct function of a control
voltage. Any current at the control terminal is simply irrelevant.

---
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.
---

Your admission that base current must
exist before collector current can exist makes the BJT a
"transresistance device",

No it don't. This is getting daft. The bipolar transistor is, to first
order, a voltage controlled current source. It is therefore a
transconductance device. Period.

---
See above.
---

since the base current is inseparable from
the base-to-emitter voltage when the BJT is operating.

Ho hummm...

---
Yes.
---

BTW, if it's singular, it's "phenomenon".
---

that charge changing
the electrical properties of the base material to more closely
approximate those of the collector and emitter. That is, when
charge is injected into the base-to-emitter diode of a PNP
transistor, the "N" type base material becomes more and more "P"
like as more and more current is forced through it, with the
result that the transistor starts looking more and more like a
single piece of low-resistance "P" type material as more and more
current flows through the base-to-emitter junction.

This is not an accurate description of the bipolar transistor. This
description is more relevant to operation of the mosfet. The npn
junction simply does not act like a slap of N type. If it did, base
current would be huge.

---
yes, were it not for the current limiting resistance external to the
base the base current could become huge.

For a given emitter current, the base current will always be a small
fraction due to transistor action. If the npn junction were just a
slab of n type then there would be a direct connection from base to
emitter resulting in larger current. You would just have resisters
connecting base emitter and collector all together and therefore no
hfe.

---
But, in fact, it _isn't_ a slab of N type material,

That's what I am claiming, you are claiming otherwise.

---
No, it isn't.

What I'm claiming is that when there is no charge being injected into
the base region, the NPN sandwich is as clearly delineated as
bread-ham-bread would be. BUT, (and it's a BIG but) when charge
starts being injected into the base region the ham starts to look more
and more like bread as more and more charged is pumped into it, with
the eventual result being that the ham looks and acts enough like
bread to take on the characteristics of bread. So, if the P type
material in the base gets enough electrons pumped into it to make it
look like N type material, then the battery connected from the
collector to the emitter will start seeing less and less resistance as
the base current gets larger and larger and will cause the collector
current to increase as the base-to-emitter voltage (and the base
current)increases.
---

it's a carefully
arranged sandwich made to become more or less resistive by changing
the electrical characteristics of the filling.
---

Therefore you are claiming by this that it *is* a slab of resistance.

---
Yes, but only when there's enough charge flowing through the base to
allow collector current to flow. Otherwise it's more like a couple of
series-opposed diodes. See above.
---

---
Hardly. Here this newbie asks "What makes a BJT different from a
FET?" and you reply "If you put a voltage across the base and
emitter terminals of a BJT current will flow between the collector
and emitter, while if you put a voltage across the gate and source
terminals of a FET current will flow between the drain and the
source." So, while your description may be true, its utter
simplicity leads the newb to think they're the same same thing with
differently named terminals.

The above statement is with regard to the control of the collector
current only. It obviously needs a statement that "base current must
exist in real device".

---
Then it's not quite as simple as "Vbe controls the collector/emitter
current.", is it?

It is, if we neglect rbb'.

---
Well, yes, everything takes on a different meaning if we start
selectively neglecting that which makes our argument untenable.
---

The fact that a source has to supply current is irrelevant.

And yet in your last post it was:

...."this base current is simply a nuisance."

Maybe in your next post it'll be: "Base current doesn't exist." ?-)

--
John Fields

 

[Miles Harris]

On Tue, 11 Jan 2005 14:30:26 -0600, John Fields
<jfields@austininstruments.com> wrote:

_My_ definition? Show me.

The definition you sought to rely on is *your* definition - de facto.

---
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?

Yes, absolutely! It is often said that "a little knowledge is a
dangerous thing" and this is where that truism is most apparent; when
hobbyists like you get out of their depth and try to 'help' other
hobbyists - as we have seen here - and simply end up making yourselves
look stupid. You should be more diligent in how you study those
'pedantic' books. Considered entry-level evening classes?

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.

It's crass to expect someone who knows even less about electronics
than you do to *know* that.

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

All the time boneheads like you keep peddling their snake oil, yes.

 

[Miles Harris]

On Tue, 11 Jan 2005 14:00:39 -0600, John Fields
<jfields@austininstruments.com> wrote:

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.

You're simply not capable. I'm a professional electronics engineer of
some 35 years experience. You, OTOH, strike me as someone who has yet
to build their first crystal set. You're out of your depth and out of
your class, pal.

[snip about datasheets]

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?

Listen, bonehead. *You* are the one who brought up the 'easy' solution
of Beta, so you explain to the OP how it so often falls apart in
practice. I never cited it, okay??
Sheesh!!!

 

[Miles Harris]

On Tue, 11 Jan 2005 17:11:16 -0600, John Fields
<jfields@austininstruments.com> wrote:

What I'm claiming is that when there is no charge being injected into
the base region, the NPN sandwich is as clearly delineated as
bread-ham-bread would be. BUT, (and it's a BIG but) when charge
starts being injected into the base region the ham starts to look more
and more like bread as more and more charged is pumped into it, with
the eventual result being that the ham looks and acts enough like
bread to take on the characteristics of bread.

ROTFLMAO!!! Hey, boner, I hope this is simply some crappy analogy
you've devised here and not directly quoted from the kind of textbooks
you've been studying!
BWAHAHAHAHAHAHAHAAAAA!!!

 

[John Fields]

On Tue, 11 Jan 2005 23:52:11 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Tue, 11 Jan 2005 14:30:26 -0600, John Fields
jfields@austininstruments.com> wrote:

_My_ definition? Show me.

The definition you sought to rely on is *your* definition - de facto.

---
Ok, now I see. Your reading comprehension is so poor that you try to
excuse yourself by casting the blame for your ignorance on someone
else.
---

---
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?

Yes, absolutely! It is often said that "a little knowledge is a
dangerous thing"

---
If that's true, then I suspect that you're extremely dangerous!
---

and this is where that truism is most apparent; when
hobbyists like you get out of their depth and try to 'help' other
hobbyists - as we have seen here - and simply end up making yourselves
look stupid.

---
Well, looks may be deceiving, but I suspect in your case that
stupidity is more than just skin deep.

Besides, what's wrong with being a hobbyist? Everybody has to start
somewhere, don't they?

What about you, what do you do?
---

You should be more diligent in how you study those
'pedantic' books. Considered entry-level evening classes?

---
Sure, and if you need some suggestions I'll be happy to post them for
you.
---

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.

It's crass to expect someone who knows even less about electronics
than you do to *know* that.

---
The _obvious_ shouldn't need an explanation. And, since even _you_
seemed to understand the point, I don't see why you'd think that
anyone else would miss it.
---

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

All the time boneheads like you keep peddling their snake oil, yes.

---
It's always "snake oil" when you don't understand and think you're
being taken advantage of by someone who does, ain't it?

BTW, did you catch the error I intentionally inserted into that little
series VS parallel LED power dissipation problem you were having so
much trouble with?

No? Hmmm...

--
John Fields

 

[John Fields]

On Tue, 11 Jan 2005 23:52:12 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Tue, 11 Jan 2005 14:00:39 -0600, John Fields
jfields@austininstruments.com> wrote:

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.

You're simply not capable. I'm a professional electronics engineer of
some 35 years experience. You, OTOH, strike me as someone who has yet
to build their first crystal set. You're out of your depth and out of
your class, pal.

---
Yup, I usually hang out with the pelagic fish, but this time I thought
I'd come up to the shallows and see what the guppies are doing. What
a surprise, there you were in a school of them!
---

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?

Listen, bonehead. *You* are the one who brought up the 'easy' solution
of Beta, so you explain to the OP how it so often falls apart in
practice. I never cited it, okay??
Sheesh!!!

---
Actually, since you seem to think you've got all the answers and that
the OP has been so wronged, why don't you make things better by taking
about a minute out of your life and writing down everything you know
about beta for his benefit? I'm sure it would be thoroughly
appreciated if you could write up to his level.

--
John Fields

 

[John Fields]

On Wed, 12 Jan 2005 00:13:27 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Tue, 11 Jan 2005 17:11:16 -0600, John Fields
jfields@austininstruments.com> wrote:

What I'm claiming is that when there is no charge being injected into
the base region, the NPN sandwich is as clearly delineated as
bread-ham-bread would be. BUT, (and it's a BIG but) when charge
starts being injected into the base region the ham starts to look more
and more like bread as more and more charged is pumped into it, with
the eventual result being that the ham looks and acts enough like
bread to take on the characteristics of bread.

ROTFLMAO!!! Hey, boner, I hope this is simply some crappy analogy
you've devised here and not directly quoted from the kind of textbooks
you've been studying!
BWAHAHAHAHAHAHAHAAAAA!!!

---
Since you obviously don't understand the analogy and are more
concerned with 'i' dotting and 't' crossing than you are with anything
technically interesting, I can't see what possible difference it would
make whether it accurately reflected reality or not. Either way, it
would be gobbledegook to you.

--
John Fields

 

[Kevin Aylward]

John Fields wrote:

On Tue, 11 Jan 2005 19:57:25 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:


"Transconductance" in the above is a pure and general
mathematically technique used to model a physical phenomena. It
doesn't care whether or not the phenomena is actually physically
current controlled by a voltage. My description that a bipolar is a
"transconductance device" is statement of its actual physics.

---

No, it's not. A true transconductance device is one in which no
current is required into the control electrode.


No. I have to say here, this is absolute nonsense. I cant believe I
am actually reading this.

---
Believe it!-)
---

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

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

---
Granted, but what you said you wanted to talk about wasn't the concept
of transconductance, it was that the "actual physics" of a BJT made it
a transconductance device. That being the case, what's nonsensical is
that almost anything can be called a transconductance device, so just
calling a BJT a transconductance device doesn't really say anything
about the physics behind it. Consider a simple potentiometer on the
bridge of a ship which is used to control the ship's speed. Is what's
being used to turn the screw a transconductance device? Sure. Does
it tell us anything about what's between the pot and the screw? No.
Same thing with a BJT. 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.

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.

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.

I have already given a link that diagrams this behaviour.

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/page2.html

---

The grid of a toob in
the region where no grid current is drawn more nearly approximates a
"true transconductance" device.

Sorry, mate, this is only *your* personal concept of a "true
transconductance" device. Somewhere you have picked up an erroneous
view without even thinking about it. The *only* requirement for a
transconductance is the output current is a direct function of a
control voltage. Any current at the control terminal is simply
irrelevant.

---
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.

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

F=q(E+vxB)

Its that simple.

---

Your admission that base current must
exist before collector current can exist makes the BJT a
"transresistance device",

No it don't. This is getting daft. The bipolar transistor is, to
first order, a voltage controlled current source. It is therefore a
transconductance device. Period.

---
See above.

See above.

For a given emitter current, the base current will always be a
small fraction due to transistor action. If the npn junction were
just a slab of n type then there would be a direct connection from
base to emitter resulting in larger current. You would just have
resisters connecting base emitter and collector all together and
therefore no hfe.

---
But, in fact, it _isn't_ a slab of N type material,

That's what I am claiming, you are claiming otherwise.

---
No, it isn't.

What I'm claiming is that when there is no charge being injected into
the base region, the NPN sandwich is as clearly delineated as
bread-ham-bread would be. BUT, (and it's a BIG but) when charge
starts being injected into the base region the ham starts to look more
and more like bread as more and more charged is pumped into it, with
the eventual result being that the ham looks and acts enough like
bread to take on the characteristics of bread. So, if the P type
material in the base gets enough electrons pumped into it to make it
look like N type material, then the battery connected from the
collector to the emitter will start seeing less and less resistance as
the base current gets larger and larger and will cause the collector
current to increase as the base-to-emitter voltage (and the base
current)increases.

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.

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.

For some reason, you have picked up an erroneous understanding of
transistor operation. You need to get to grips with the idea that you
have been mistaken on this issue. This isn't debatable. Its in all the
academic text books.

Look, actually produce a detailed *physics* explanation as to *how* a
flow of base charge can actually induce a flow of collector charge. This
should tell you something.

In all the semiconductor text books I have read, I have never seen this
done, so why you can claim that this is the case, is pretty far fetched
indeed.

---

it's a carefully
arranged sandwich made to become more or less resistive by changing
the electrical characteristics of the filling.
---

Therefore you are claiming by this that it *is* a slab of resistance.

---
Yes, but only when there's enough charge flowing through the base to
allow collector current to flow. Otherwise it's more like a couple of
series-opposed diodes. See above.

And this is wrong.

---

---
Hardly. Here this newbie asks "What makes a BJT different from a
FET?" and you reply "If you put a voltage across the base and
emitter terminals of a BJT current will flow between the collector
and emitter, while if you put a voltage across the gate and source
terminals of a FET current will flow between the drain and the
source." So, while your description may be true, its utter
simplicity leads the newb to think they're the same same thing
with differently named terminals.

The above statement is with regard to the control of the collector
current only. It obviously needs a statement that "base current
must exist in real device".

---
Then it's not quite as simple as "Vbe controls the collector/emitter
current.", is it?

It is, if we neglect rbb'.

---
Well, yes, everything takes on a different meaning if we start
selectively neglecting that which makes our argument untenable.

Which isn't the case here. The error due to rbb' is usually small. It
doesn't change the bipolar from its fundamental physics description as a
voltage controlled device. Rbb' just makes the calculation of the
voltage a little more involved.

---

The fact that a source has to supply current is irrelevant.

And yet in your last post it was:

..."this base current is simply a nuisance."

There is no conflict here.

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Miles Harris]

On Tue, 11 Jan 2005 18:34:47 -0600, John Fields
<jfields@austininstruments.com> wrote:

Ok, now I see. Your reading comprehension is so poor that you try to
excuse yourself by casting the blame for your ignorance on someone
else.

Nope. You quoted this half-baked definition so it's quite proper for
others to infer you're happy with it.

[snip juvenile insults]

It's always "snake oil" when you don't understand and think you're
being taken advantage of by someone who does, ain't it?

That's rich, coming from someone who doesn't even understand
transistor action. Your concept of it would have Shockley turning in
his grave.

BTW, did you catch the error I intentionally inserted into that little
series VS parallel LED power dissipation problem you were having so
much trouble with?

Translation: "Holy shit! I've made the kind of dumbass error in that
LED thread typical of a bonehead like me. Let's hope I can get away
with this half-baked excuse before Miles spots it and I get exposed as
an even *bigger* bonehead!"

 

[Miles Harris]

On Tue, 11 Jan 2005 18:45:40 -0600, John Fields
<jfields@austininstruments.com> wrote:

Actually, since you seem to think you've got all the answers and that
the OP has been so wronged, why don't you make things better by taking
about a minute out of your life and writing down everything you know
about beta for his benefit? I'm sure it would be thoroughly
appreciated if you could write up to his level.

It would, as you no doubt know, take me a great deal longer than one
minute to write out everything I know about Beta. But were I so
inclined, at least the OP would have an extensive, complete and
accurate grasp of the subject, rather than the false sense of
competence you attempted to instill in him by means of your own.
HTH.

 

[John Fields]

On Wed, 12 Jan 2005 10:58:07 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Tue, 11 Jan 2005 18:34:47 -0600, John Fields
jfields@austininstruments.com> wrote:

Ok, now I see. Your reading comprehension is so poor that you try to
excuse yourself by casting the blame for your ignorance on someone
else.

Nope. You quoted this half-baked definition so it's quite proper for
others to infer you're happy with it.

---
I _am_ happy with it, regardless of whether you choose to take issue
with it or not. After all, your objections to it are largely
unfounded in that from the context of the definition everything being
described was quite clear.
---

It's always "snake oil" when you don't understand and think you're
being taken advantage of by someone who does, ain't it?

That's rich, coming from someone who doesn't even understand
transistor action. Your concept of it would have Shockley turning in
his grave.

---
That's rich, coming from someone who didn't even know how to determine
the difference in power dissipation between circuits in parallel and
in series
---

BTW, did you catch the error I intentionally inserted into that little
series VS parallel LED power dissipation problem you were having so
much trouble with?

Translation: "Holy shit! I've made the kind of dumbass error in that
LED thread typical of a bonehead like me. Let's hope I can get away
with this half-baked excuse before Miles spots it and I get exposed as
an even *bigger* bonehead!"

---
Miles, is it? Should be more like Inches...

Never mind the bullshit, can you find it? Yes or no? Or are you
going to slither out of it with another one of your lame-ass dodges?

--
John Fields

 

[John Fields]

On Wed, 12 Jan 2005 10:58:08 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Tue, 11 Jan 2005 18:45:40 -0600, John Fields
jfields@austininstruments.com> wrote:

Actually, since you seem to think you've got all the answers and that
the OP has been so wronged, why don't you make things better by taking
about a minute out of your life and writing down everything you know
about beta for his benefit? I'm sure it would be thoroughly
appreciated if you could write up to his level.

It would, as you no doubt know, take me a great deal longer than one
minute to write out everything I know about Beta. But were I so
inclined, at least the OP would have an extensive, complete and
accurate grasp of the subject, rather than the false sense of
competence you attempted to instill in him by means of your own.
HTH

---
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?

--
John Fields

 

[John Fields]

On Wed, 12 Jan 2005 10:58:09 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

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.

---
And you're the exception that proves the rule?


--
John Fields

 

[Bob Myers]

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...

Bob M.

 

[John Fields]

On Wed, 12 Jan 2005 10:58:09 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

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.

---
Speaking of obtuseness, you seem to have (after all the ass-kissing)
missed the part that was missing. That is, the role that Vce plays in
generating the collector current.

Kevin states that: "It is the electric field at Vbe that causes both
base current and collector/emitter current"...

While it's true that Vbe causes Ib to flow and is, of course, a
contributor to the flow of Ic, the implication is that all of the
collector current flowing through the base region is due solely to
Vbe, and that with a given Vbe and no Vce, the emitter current will be
what it would have been had the collector been connected to a source
odf voltage. In other words, the collector current which would
normally have been making its way to the collector because of the
attraction of Vce drawing it away from the base will now make its way
to the base because of the lack of Vce. Such is not the case.


Consider this case with Ic flowing:

183mA--> 2N4401
[HP6285A]-----[FLUKE 8060A]----------C E-----GND
B
1.8mA--> |
[HP6216A]-----[WAVETEK 27XT]-----------+




and this, with no Ic flowing:

2N4401
C E-----GND
B
15.1mA--> |
[HP6216A]-----[WAVETEK 27XT]-----------+


Both power supplies were set up as voltage sources with no current
limiting and adjusted to give the readings obtained in the upper
example. The collector supply was then disconnected from the
collector and the reading shown in the lower example was obtained.
About a tenfold increase in base current because the collector current
was no longer causing a voltage drop across the base-emitter diode,
but certainly not the hundred-fold increase one would expect if Vbe
were the sole contributor to the cause of Ic.



BTW, since I find you mildly annoying I decided to take a look at your
posting history to see what you're about, and I found that other than
about the 20 posts archived at Google (where you also seem to have an
attitude) you seem only to have posted here, so welcome to the swamp.

While looking, I found this rather interesting post on this NG:

<QUOTE>
On Fri, 31 Dec 2004 17:29:24 -0000, "Andrew Holme" <andrew@nospam.com>
wrote:

Didoes drop voltage not current. Silicon diodes (e.g. 1N4148 or 1N4001)
drop about 0.7V so one would probably be adequate; but two, in series, would
be safer.

Um, yeah, but they drop voltage _according_ to current! If they're
dropping 0,7V., they're not passing much current! Diodes are a crap
way to drop voltage unless the load is light and predictable!!!

miles
<END QUOTE>

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

Continuing on, we find, from Danny T:

<QUOTE>
http://www.kpsec.freeuk.com/components/diode.htm

says

"There is a small voltage across a conducting diode, it is called the
forward voltage drop and is about 0.7V for all normal diodes which are
made from silicon. The forward voltage drop of a diode is almost
constant whatever the current passing through the diode so they have a
very steep characteristic (current-voltage graph)."

--
Danny
<END QUOTE>


To which you replied:

The forward voltage drop is entirely dependent on temperature (the
junction temp. of the p/n junction; which is in turn dependent upon
the current passed.) Higher currents equals higher temp. equals lower
voltage drop. It's a well known effect which can eventually destroy
the diode altogether. The physics of diodes is actually more complex
than a lot of texts would have you believe.

---
Indeed, but if you think the forward voltage drop is _entirely_
dependent on temperature, you seem to have missed reading some of the
more fundamental ones.

For example, while it's certainly true that the voltage across the
junction can be described by:


kT / If \
Vf = ---- ln ( 1 + ---- )
q \ Ir /

and that when T is equal to zero at 0°K, Vf will be 0, you've
neglected to mention that current passing through the bulk resistance
of the diode, at any temperature, will cause a drop across the
junction which is dependent on the resistance and the charge flowing
through the diode.

More importantly, perhaps, you pooh-pooh'd Danny T's idea to use a
diode as a bad one merely because of your opinion, which was
erroneous. Diodes are _often_ used as voltage dropping elements in
the real world because of the small change in Vf caused by If.
Moreover, your example of the negative TC of a diode destroying it
would more closely describe a diode with a voltage source connected
across it allowing the diode to get into thermal runaway. Such a
condition would not happen with the load limiting the current through
the diode and the diode sized to carry the required current under the
required environmental conditions. Furthermore, depending on the
diode, above a certain current the tempco becomes positive, something
else you "neglected" to mention.

What's most disturbing, however, is that with Danny T admittedly being
a newbie and asking for information, you deliberately sidestepped the
issue when he presented you with the [valid] information he found
which supported Andrew Holmes' suggestion to use a diode in order to
keep from having to admit that you were wrong in stating that: "Diodes
are a crap way to drop voltage unless the load is light and
predictable!!!

For shame, sir! :-(















--
John Fields

 

[Miles Harris]

On Wed, 12 Jan 2005 11:53:01 -0600, John Fields
<jfields@austininstruments.com> wrote:

Never mind the bullshit, can you find it? Yes or no? Or are you
going to slither out of it with another one of your lame-ass dodges?

Oh, your assignment question? Listen, Junior, that's for your teacher
to explain to you. I owe you no such favors. Stick with your studies,
though; you may make it one day - if *you* work through your own
homework instead of trying to trick others into doing it for you.

 

[Miles Harris]

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

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?

"Of course they're wrong, but so what?"????
The mind boggles.
I do appreciate the dilemma, though. On the one hand we'd like to
convey a complete understanding of the subject to the questioner. On
the other hand, we suspect that if we did so, they'd find it all too
much, be turned off and simply find another hobby to pursue.

Perhaps the answer is to provide the simpler explanation, based on the
questioner's level of knowledge, but spell out the caveat that there
is more to the topic than has been explained in the follow-up. IOW,
tell the questioner that the answer provided is sufficient for their
current purposes, but they may need to take more on board as they
advance in their studies.

 

[Miles Harris]

On Wed, 12 Jan 2005 15:20:16 -0600, John Fields
<jfields@austininstruments.com> wrote:

[snip pointless, uncalled-for lecture on base current but maybe some
newbie can make use of it]

BTW, since I find you mildly annoying I decided to take a look at your
posting history to see what you're about, and I found that other than
about the 20 posts archived at Google (where you also seem to have an
attitude) you seem only to have posted here, so welcome to the swamp.

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....

While looking, I found this rather interesting post on this NG:

QUOTE
On Fri, 31 Dec 2004 17:29:24 -0000, "Andrew Holme" <andrew@nospam.com
wrote:

Didoes drop voltage not current. Silicon diodes (e.g. 1N4148 or 1N4001)
drop about 0.7V so one would probably be adequate; but two, in series, would
be safer.

Um, yeah, but they drop voltage _according_ to current! If they're
dropping 0,7V., they're not passing much current! Diodes are a crap
way to drop voltage unless the load is light and predictable!!!

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.

Continuing on, we find, from Danny T:

QUOTE
http://www.kpsec.freeuk.com/components/diode.htm

says

"There is a small voltage across a conducting diode, it is called the
forward voltage drop and is about 0.7V for all normal diodes which are
made from silicon. The forward voltage drop of a diode is almost
constant whatever the current passing through the diode so they have a
very steep characteristic (current-voltage graph)."

--
Danny
END QUOTE


To which you replied:

The forward voltage drop is entirely dependent on temperature (the
junction temp. of the p/n junction; which is in turn dependent upon
the current passed.) Higher currents equals higher temp. equals lower
voltage drop. It's a well known effect which can eventually destroy
the diode altogether. The physics of diodes is actually more complex
than a lot of texts would have you believe.

---
Indeed, but if you think the forward voltage drop is _entirely_
dependent on temperature, you seem to have missed reading some of the
more fundamental ones.

For example, while it's certainly true that the voltage across the
junction can be described by:


kT / If \
Vf = ---- ln ( 1 + ---- )
q \ Ir /

and that when T is equal to zero at 0°K, Vf will be 0, you've
neglected to mention that current passing through the bulk resistance
of the diode, at any temperature, will cause a drop across the
junction which is dependent on the resistance and the charge flowing
through the diode.

More importantly, perhaps, you pooh-pooh'd Danny T's idea to use a
diode as a bad one merely because of your opinion, which was
erroneous. Diodes are _often_ used as voltage dropping elements in
the real world because of the small change in Vf caused by If.
Moreover, your example of the negative TC of a diode destroying it
would more closely describe a diode with a voltage source connected
across it allowing the diode to get into thermal runaway. Such a
condition would not happen with the load limiting the current through
the diode and the diode sized to carry the required current under the
required environmental conditions. Furthermore, depending on the
diode, above a certain current the tempco becomes positive, something
else you "neglected" to mention.

What's most disturbing, however, is that with Danny T admittedly being
a newbie and asking for information, you deliberately sidestepped the
issue when he presented you with the [valid] information he found
which supported Andrew Holmes' suggestion to use a diode in order to
keep from having to admit that you were wrong in stating that: "Diodes
are a crap way to drop voltage unless the load is light and
predictable!!!

For shame, sir! :-(

It can hardly be described as "disturbing" FFS.
Excuse me for not having the time or inclination to wade through your
entire post and answer every individual point; but if you're trying to
suggest that I'm as guilty as you in giving 'easy' and expedient
explanations to newbies that don't reflect the full picture, then I
guess I'd have to plead guilty. None of us are perfect.
If you don't like it, sue me.

 

[John Fields]

On Thu, 13 Jan 2005 10:38:23 GMT, Miles Harris <mazzer@yahoo.com>
wrote:

On Wed, 12 Jan 2005 11:53:01 -0600, John Fields
jfields@austininstruments.com> wrote:

Never mind the bullshit, can you find it? Yes or no? Or are you
going to slither out of it with another one of your lame-ass dodges?

Oh, your assignment question? Listen, Junior, that's for your teacher
to explain to you. I owe you no such favors. Stick with your studies,
though; you may make it one day - if *you* work through your own
homework instead of trying to trick others into doing it for you.

---
LOL! Just as I thought; another lame-ass dodge!

BTW, there was no error. I just wanted to see if you could come to
that conclusion and, obviously, you couldn't. No surprise, really,
after reading some of your other trash.

--
John Fields