FETs Vesus Bipolars, Why More Efficient?

[Winfield Hill]

Dr. Slick wrote...

Winfield Hill wrote ...
Dr. Slick wrote...

Why do you think that? CCCS for bipolars and VCCS for
FETs is standard in most texts.

That's why when you look at a I-V curves, for BJTs the
lines are denoted with base current, and for FETs the lines
are denoted with gate voltage.

Nope.

Not a very convincing argument!

Read our textbook, AoE, you'll find my argument well stated.


--
Thanks,
- Win

 

[Paul Burridge]

On Sat, 13 Nov 2004 10:37:31 +0100, "Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:

Please, tell us more

Oh, I couldn't possibly. ;-)

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Dr. Slick]

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in message news:<cn53g60g1@drn.newsguy.com>...

Dr. Slick wrote...

The point is that MOSFETs have far less gate current
than do BJTs have base current.

At high frequencies you may find just the opposite is true.

Bullshit.

 

[Paul Burridge]

On 13 Nov 2004 15:29:46 -0800, radio913@aol.com (Dr. Slick) wrote:

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in message news:<cn53g60g1@drn.newsguy.com>...
Dr. Slick wrote...

The point is that MOSFETs have far less gate current
than do BJTs have base current.

At high frequencies you may find just the opposite is true.

Bullshit.

Don't pay any attention, Win. This guy is a notorious idiot from
rec.radio.amateur.antenna and he just *loves* wind people up.

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Guy Macon]

Dr. Slick wrote:

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu
wrote in message news:<cn53g60g1@drn.newsguy.com>...

Dr. Slick wrote...

The point is that MOSFETs have far less gate current
than do BJTs have base current.

At high frequencies you may find just the opposite is true.

Bullshit.

You don't have a clue as to who you are talking to, do you?
Read this: [ http://www.artofelectronics.com/ ]

 

[Ken Smith]

In article <1d15af91.0411130357.59c8d060@posting.google.com>,
Dr. Slick <radio913@aol.com> wrote:

kensmith@green.rahul.net (Ken Smith) wrote in message
news:<cn2n2r$sun$2@blue.rahul.net>...


Parasitic inductance is usually less than about 2nH,
so it would be about XL=2*pi*f*L

So the inductive reactance would be about 1.25 Ohms
at 100 MHz. Certainly affecting the impedance, but
still pretty low.

Instead of counting on my memory. I dug out the BLF276's data sheet.

At 100MHz Zin = 1.3 -j1.7 (points taken from graph)

A 1.25Ohms Xl would be very important in this case since it is about as
big as R and Xc. Th package on this is a 6 pins as source configuration.


mag[Z]=sqrt(1.3**2+1.7**2)

so it's still going to be low impedance.

Now look at the angle. When you go to match down to the low impedance, it
really matters about the phase.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <1d15af91.0411131529.7a9d45a8@posting.google.com>,
Dr. Slick <radio913@aol.com> wrote:

Winfield Hill <hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in
message news:<cn53g60g1@drn.newsguy.com>...
Dr. Slick wrote...

The point is that MOSFETs have far less gate current
than do BJTs have base current.

At high frequencies you may find just the opposite is true.

Bullshit.

Compare the base current on a 2N5641 making 3W of 100MHz to the gate
current of any MOSFET you care to select, and I expect you will find it
certainly is true.

I mension the 2N5641 because I tried to find a MOSFET equivelent and could
not for exactly this reason.


--
--
kensmith@rahul.net forging knowledge

 

[Guy Macon]

Dr. Slick wrote:

"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote:

[snip]

Just killfile him, doc. He is ineducable, and life is too short to
spend arguing with someone who is never, ever wrong about anything.

 

[Winfield Hill]

Kevin Aylward wrote...

You're doing yourself quite a disservice dude.

Don't worry about it Kevin, "Dr. Slick" must be a troll.


--
Thanks,
- Win

 

[Ken Smith]

In article <1d15af91.0411120556.6d528ee3@posting.google.com>,
Dr. Slick <radio913@aol.com> wrote:

kensmith@green.rahul.net (Ken Smith) wrote in message
news:<cn0udv$2tg$2@blue.rahul.net>...

yeah, the series parasitic inductance too, but
you have to get into UHF or microwaves before
they get bad.

Depends on what you call bad. With higher power MOSFETs (BLF276 IIRC) the
input impedance hits zero angle before 200MHz so at 100MHz, it will be
effecting the impedance.


Parasitic inductance is usually less than about 2nH,
so it would be about XL=2*pi*f*L

So the inductive reactance would be about 1.25 Ohms
at 100 MHz. Certainly affecting the impedance, but
still pretty low.

Instead of counting on my memory. I dug out the BLF276's data sheet.

At 100MHz Zin = 1.3 -j1.7 (points taken from graph)

A 1.25Ohms Xl would be very important in this case since it is about as
big as R and Xc. Th package on this is a 6 pins as source configuration.

--
--
kensmith@rahul.net forging knowledge

 

[Dr. Slick]

"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote in message news:<%QJld.12051$P7.10198@fe2.news.blueyonder.co.uk>...

Well, it can be either base current or Vbe, obviously.

You still miss the point. Basic physics dictates that the flow of
charge, i.e. current is instigared by applying an electric field, i.e. a
voltage, not another current.

No argument there. You have to apply a voltage to
induce a current flow. You should write a book!

But you talk about the "Beta current gain factor" as
(delta Collector current)/(delta base current), and they
don't describe FETs like this.

However, you are correct that "gm" or "transconductance"
can be either dIdrain/dVgate or dIc/dVbe.

Trying to teach your grandpa to suck eggs I see.

I'll teach yo' momma to suck THIS!

The point is that MOSFETs have far less gate current
than do BJTs have base current.

Then this is what should be said. This base current controlled nonsense
is fundamentally incorrect, and leads to much confusion. A bipolar
transistor is a voltage controlled device that just happens to have a
non-linear resistance strapped across it.

Read any basic electrons textbook, and they
will talk about Beta current gain:


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

And this is one you need to read too:

http://www.americanmicrosemi.com/tutorials/mosfets.htm



Slick

 

[Paul Burridge]

On Sun, 14 Nov 2004 15:40:52 +0100, "Fred Bartoli"
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:

"Jim Thompson" <thegreatone@example.com> a écrit dans le message de
news:cvgcp0hg2ud2ocgu21eovicehdnb5sgdqv@4ax.com...
On Sat, 13 Nov 2004 10:37:31 +0100, "Fred Bartoli"
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:


"Paul Burridge" <pb@notthisbit.osiris1.co.uk> a écrit dans le message de
news:16gap0138huajj8b3k0abf2h76opodmd39@4ax.com...
[snip]

FETs are certainly accurately modelled as VCCS in a certain regions of
operation. BJTs are *inaccurately* modelled as CCCS. Vbe's what you
really want to look at with BJTs.

Please, tell us more

Paul doesn't have a clue... he's just parroting ;-)


Yes indeed. And we also all know where his remark came from...
I just feel sometimes a bit irritated when, more often than not, he plays Mr
know it all and shouts things he picked here and there, and he have no clue
about.

I get criticised when I *don't* remember things I've been told and you
say you find it irritating when I *do* so I can't win, can I?

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On 14 Nov 2004 08:52:53 -0800, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Kevin Aylward wrote...

You're doing yourself quite a disservice dude.

Don't worry about it Kevin, "Dr. Slick" must be a troll.

He's not a doctor of anything but he does - believe it or not - have
an E.E degree.

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[ChrisGibboGibson]

Jim Thompson wrote:

[snip]

Forcing a current doesn't induce a voltage ?

In a superconducting inductor?

Gibbo

 

[Guy Macon]

Jim Thompson wrote:

You have to apply a voltage to induce a current flow.

Forcing a current doesn't induce a voltage ?

Hmmm.

A voltage may exist with no current (insulator).

A current may exist with no voltage (superconductor).

A voltage without current has an electric field but no magnetic field.

A current without voltage has a magnetic field but no electric field.

At one point in history physicists described nature as having 5
fundamental forces: the electric force, the magnetic force, the
strong nuclear force, the weak nuclear force, and the gravitational
force.

In 1856 James Clerk Maxwell (1831-1879), building on Faraday's
work, unified the electric force and the magnetic force into the
electromagnetic force. Faraday was self-taught and had never
mastered mathematics, but (unlike the case with a certain bigot
here who regularly flames the self-taught) this didn't stop
Maxwell from learning from Faraday's work.

I thus conclude that it is meaningless to claim that a voltage
"causes" a current or that a current "causes" a voltage. One
might as well claim that it resistance "causes" voltage and that
conductance "causes" current.

 

[Paul Burridge]

On 14 Nov 2004 14:36:54 -0800, radio913@aol.com (Dr. Slick) wrote:

No argument there. You have to apply a voltage to
induce a current flow. You should write a book!

Erm, no. You could just induce a magnetic field...
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Ken Smith]

In article <10pfujicb0d43f@corp.supernews.com>,
Guy Macon <http://www.guymacon.com> wrote:
[...]

I thus conclude that it is meaningless to claim that a voltage
"causes" a current or that a current "causes" a voltage. One
might as well claim that it resistance "causes" voltage and that
conductance "causes" current.

Everything can be explained as the actions of invisible magic unicorns.
They cause the digits to appear on your DVM and fool you into thinking
that there is a voltage and a current. In fact neither exist.

The universe was formed some 15E9 years ago so we know that no voltages or
currents have been around longer than that. This sets a lower limit on
the frequency and hence the energy of the photons that are the real story.



--
--
kensmith@rahul.net forging knowledge

 

[Rich The Philosophizer]

On Sun, 14 Nov 2004 22:41:43 +0000, Paul Burridge wrote:

On Sun, 14 Nov 2004 15:40:52 +0100, "Fred Bartoli"
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:


"Jim Thompson" <thegreatone@example.com> a écrit dans le message de
news:cvgcp0hg2ud2ocgu21eovicehdnb5sgdqv@4ax.com...
On Sat, 13 Nov 2004 10:37:31 +0100, "Fred Bartoli"
fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote:


"Paul Burridge" <pb@notthisbit.osiris1.co.uk> a écrit dans le message de
news:16gap0138huajj8b3k0abf2h76opodmd39@4ax.com...
[snip]

FETs are certainly accurately modelled as VCCS in a certain regions of
operation. BJTs are *inaccurately* modelled as CCCS. Vbe's what you
really want to look at with BJTs.

Please, tell us more

Paul doesn't have a clue... he's just parroting ;-)


Yes indeed. And we also all know where his remark came from...
I just feel sometimes a bit irritated when, more often than not, he plays Mr
know it all and shouts things he picked here and there, and he have no clue
about.

I get criticised when I *don't* remember things I've been told and you
say you find it irritating when I *do* so I can't win, can I?

Nah. Can't break even either. Can't even quit the game. You're damned
if you do, and damned if you don't.

For these times, when you're at a crossroads of life, and the signs
all say, "STOP" "DO NOT ENTER" "NO RIGHT TURN" "NO LEFT TURN" "NO
U-TURN" "NO PARKING" and "Do Not Back Up, Sever Tire Damage!", I
always fall back on the short-form Serenity Prayer:

"Fuck it."

;^j
Rich

 

[Kevin Aylward]

Guy Macon wrote:

Jim Thompson wrote:

You have to apply a voltage to induce a current flow.

Forcing a current doesn't induce a voltage ?

Hmmm.

A voltage may exist with no current (insulator).

A current may exist with no voltage (superconductor).

A voltage without current has an electric field but no magnetic field.

A current without voltage has a magnetic field but no electric field.

At one point in history physicists described nature as having 5
fundamental forces: the electric force, the magnetic force, the
strong nuclear force, the weak nuclear force, and the gravitational
force.

In 1856 James Clerk Maxwell (1831-1879), building on Faraday's
work, unified the electric force and the magnetic force into the
electromagnetic force. Faraday was self-taught and had never
mastered mathematics, but (unlike the case with a certain bigot
here who regularly flames the self-taught) this didn't stop
Maxwell from learning from Faraday's work.

Things are way different now. A country bumpkin will never contribute to
physics today. Its way to advanced.

I thus conclude that it is meaningless to claim that a voltage
"causes" a current or that a current "causes" a voltage. One
might as well claim that it resistance "causes" voltage and that
conductance "causes" current.

Yes, in the *bigger* scheme of things, its all arbitrary models, but
this discussion is at an engineering level, and at that level the
"correct" model of a transistor is as a voltage controlled device. One
has to draw a line somewhere in treating somthing as relativly "correct"
and something else as relativly "wrong".

If we *want* to get into the bigger philosophical picture, then electric
and magnetic field are both fictitious, That is they cannot possibly be
physically real. This is because Relativity shows that, for example, a
magnetic field is simply an electric field viewed from a different frame
of reference. How is it possible of a real object to actually cease to
exit and then re-exist, just because of the observers change in motion?
What is considered the real object in E&M is the Electromagnetic field
tensor. This is an object that is frame independent. Real objects in
physics are considered to be frame invariant.

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.

 

[Kevin Aylward]

Dr. Slick wrote:

"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote in message
news:<%QJld.12051$P7.10198@fe2.news.blueyonder.co.uk>...

Well, it can be either base current or Vbe, obviously.

You still miss the point. Basic physics dictates that the flow of
charge, i.e. current is instigared by applying an electric field,
i.e. a voltage, not another current.


No argument there. You have to apply a voltage to
induce a current flow. You should write a book!





But you talk about the "Beta current gain factor" as
(delta Collector current)/(delta base current), and they
don't describe FETs like this.

However, you are correct that "gm" or "transconductance"
can be either dIdrain/dVgate or dIc/dVbe.

Trying to teach your grandpa to suck eggs I see.


I'll teach yo' momma to suck THIS!






The point is that MOSFETs have far less gate current
than do BJTs have base current.

Then this is what should be said. This base current controlled
nonsense is fundamentally incorrect, and leads to much confusion. A
bipolar transistor is a voltage controlled device that just happens
to have a non-linear resistance strapped across it.



Read any basic electrons textbook, and they
will talk about Beta current gain:

You would be better going to http://www.anasoft.co.uk/EE/index.html

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

Note the nice graphs on
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/page2.html

e.g. "...The precise value of the chosen Emitter-Base voltage isn't
important to our argument here, but it does determine the amount of
current we'll see...."

Its a reasonable layman's description, with pictures, of how a
transistor actually works, so you should study it well. You will learn
much from it, probably... well maybe...

And this is one you need to read too:

http://www.americanmicrosemi.com/tutorials/mosfets.htm

You out of your depth mate.

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.