Biasing bipolar transistors

[Dave]

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build the
damn thing every time to *see* if it works.

Many thanks,

Dave

 

[Jasen Betts]

On 2009-12-21, Dave <db5151@hotmail.com> wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way,

applied algebra.

V_be = constant
I_e = -Ib * H_fe

 

[pimpom]

Dave wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I
just don't know what it is, and am thinking that it's not necessary
to build the damn thing every time to *see* if it works.

The question must first be asked: optimum in what respect? There are several
factors that may influence the choice of biasing circuit. E.g., -
- stability with variations in temperature
- stability with variations in power supply
- stability with variations in transistor characteristics from sample to
sample
- for linear amplification, expected amplitude of input and output swing
and there are others like noise, frequency response, impedance, gain, power
dissipation, waveform distortion, dc and ac feedback, etc.

 

[Andrew Holme]

"Dave" <db5151@hotmail.com> wrote in message
news:x9-dnXPZ3NzrkLLWnZ2dnUVZ_jKdnZ2d@posted.internetamerica...

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build
the damn thing every time to *see* if it works.

Many thanks,

Dave

Simulation?

Why not use LTSpice? It's fantastic and free.

I'm playing with it right now, studying an old design for a discrete
transistor DC amplifier.

 

[Tim Wescott]

On Sun, 20 Dec 2009 23:53:55 -0600, Dave wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build
the damn thing every time to *see* if it works.

Many thanks,

Dave

I use Vbe = 0.6V (or so) and do it on paper for a first cut (if you want
things to work over temperature remember that Vbe can be quite different
at -40C and +55C). Then I use LTSpice to verify that I didn't have my
head stuck deeply into my assumptions.

Then, since I have LTSpice open anyway, I use it to check the rest of the
circuit.

Remember that there are a whole bunch of ways to bias a transistor
circuit from amazingly simple to simply amazing; all have their place and
what's 'optimum' for one circuit is often woefully inadequate or terrible
overkill for another.

--
www.wescottdesign.com

 

[Jon Kirwan]

On Sun, 20 Dec 2009 23:53:55 -0600, "Dave" <db5151@hotmail.com> wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build the
damn thing every time to *see* if it works.

Single BJT common emitter voltage amp? If so, I can walk you through
some of the details.

Jon

 

[Charles]

http://www.ee.cityu.edu.hk/~hkng/doc07_08/L07%20DC%20and%20AC%20Load%20Line.ppt#7

Please check this out ... I think it fits your needs.

 

[John Larkin]

On Sun, 20 Dec 2009 23:53:55 -0600, "Dave" <db5151@hotmail.com> wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build the
damn thing every time to *see* if it works.

Many thanks,

Dave

Building it is the worst way to design the bias bits, unless you
intend to only ever build one. Transistor betas can vary over a 10:1
range, and Vbe changes about 2.5 millivolts per degree C, and
transistors often self-heat. A bias design should be reasonably
insensitive to those effects.

If you can't do it analytically, simulate it with LT Spice. But vary
beta and Vbe to make sure it will work over the full datasheet beta
range and over temperature.

John

 

[Edmond H. Wollmann]

"Andrew Holme" <ah@nospam.co.uk> wrote in message news:umJXm.102934$2u1.52673@newsfe16.ams2...

"Dave" <db5151@hotmail.com> wrote in message
news:x9-dnXPZ3NzrkLLWnZ2dnUVZ_jKdnZ2d@posted.internetamerica...
How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I just
don't know what it is, and am thinking that it's not necessary to build
the damn thing every time to *see* if it works.

Many thanks,

Dave



Simulation?

Why not use LTSpice? It's fantastic and free.

I'm playing with it right now, studying an old design for a discrete
transistor DC amplifier.

It will rust your brain.

 

[Kevin Aylward]

Dave wrote:

How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I
just don't know what it is, and am thinking that it's not necessary
to build the damn thing every time to *see* if it works.

Many thanks,

Dave

Use a Spice simulation program that has automatic worst case analysis.

Kevin Aylward

www.anasoft.co.uk
SuperSpice

 

[Jon Kirwan]

On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
<kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I
just don't know what it is, and am thinking that it's not necessary
to build the damn thing every time to *see* if it works.

Many thanks,

Dave

Use a Spice simulation program that has automatic worst case analysis.

Kevin Aylward

www.anasoft.co.uk
SuperSpice

Hi, Kevin. Been a while.

I think the OP wrote "while it's still all on paper." Which is a
skill worth working on, even if "optimum" is never fully achieved and
even if the OP didn't say what the circumstances were. It means the
OP needs to get a handle on BJTs, which is good.

For some specific, worked examples of designing a degenerative 1-BJT
common emitter voltage amp stage, the better I've seen done by hand
were in the Student Manual for the Art of Electronics, 2nd ed. Not
the textbook, but the student manual, where it walks one through a
cookbook ordering of steps with some whys. Together with the
textbook, it's decent.

I remember your descriptions and your web links (which I appreciated)
regarding these things, too. But one needs a little more background,
I think, to appreciate the approaches better.

Also, the OP provides _no_ information about their own background,
skills, what they feel they understand. The one thing we do know is
that the OP does _not_ feel they understand "BJT biasing," for
whatever purpose they may have in mind.

Two things that helped me quite a bit, book-learning wise and aside
from AofA and its student manual, were:

Ian Getreu's "Modeling the Bipolar Transistor," 1979 printing
of the 1976 book; and,
Andrei Vladimirescu's "The SPICE Book," 1994

Ian's book has been digitized and made available from Lulu, about a
month ago. (Tektronix was the prior publisher and they stopped doing
that in 1979.) One of the things it does is to approach, for those
interested, the BJT models from a physical understanding approach
starting with Ebers & Moll's 1954 paper and moving forward with
explanations and reasons along the way through Gummel-Poon (1970).
These include excellent graphs and charts which illustrate in great
detail many important elements in a way I haven't seen in print
before. That's the first half of the book. The other half is about
how to set up and measure the parameter values, which enhances the
theory a great deal I think.

Clive Maxfield has done a recent review:

http://www.techbites.com/200912221556/myblog/reviews/z000c-book-review-modeling-the-bipolar-transistor.html

But without knowing much about the OP or what problem is being worked,
it's really hard to know what to suggest. And the OP has remained
silent on this. Oh, well.

Hope you are doing fine,
Jon

 

[pimpom]

Jon Kirwan wrote:

On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a
bipolar
transistor, while it's still all on paper? There must be a
way, I
just don't know what it is, and am thinking that it's not
necessary
to build the damn thing every time to *see* if it works.


But without knowing much about the OP or what problem is being
worked,
it's really hard to know what to suggest. And the OP has
remained
silent on this. Oh, well.

Perhaps I scared him off with my earlier reply, saying that
certain criteria should first be defined to make the term
"optimum" meaningful, while citing several examples of such
criteria. If that's the case, it was not my intention.

 

[Dave]

"pimpom" <pimpom@invalid.invalid> wrote in message
news:hh0g2n$mth$1@news.albasani.net...

Jon Kirwan wrote:
On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I
just don't know what it is, and am thinking that it's not necessary
to build the damn thing every time to *see* if it works.


But without knowing much about the OP or what problem is being worked,
it's really hard to know what to suggest. And the OP has remained
silent on this. Oh, well.


Perhaps I scared him off with my earlier reply, saying that certain
criteria should first be defined to make the term "optimum" meaningful,
while citing several examples of such criteria. If that's the case, it was
not my intention.

Hey pimpom,

No no, not scared, off, trying to get a handle on all that was mentioned for
thorough understanding and application of such. Still working on it, as I
only have a little time each day to work on this.

What I am trying to do: build a "hearing aid" for my shortwave radio,
essentially an RF amplifier that I can tune, which will filter out most of
the crap surrounding the station of interest, before feeding the output to
my Sony ICF 7600 for further cleanup/amplification. Originally tried
working with JFETs, but gave up on that when I found they don't really offer
any greater amplification than bipolars. Finally settled on the NTE199 (and
I don't know what that replaces) due to it's minimum 400Hfe. Am thinking
three of these in series would probably suffice for what I am wanting.
Found a biasing tutorial at
www.hobbyprojects.com/junction_transistors/biasing_a_transistor.html (think
I have that right,)which looks helpful, and am fiddling with it at the
moment. Also hitting the books again, so I can understand what it is I am
trying to do (Electronic Principles-Malvino and Art of Electronics-Horowitz
& Hill, 2nd ed).

My background: Taught myself the fundamentals of electronics in high school
(30+ years ago) and went to a trade school to get a better understanding of
such. Worked on peripheral computer equipment in a mainframe environment
and than in a mini-system/small business environment for 12 years before
auto-accident/head injury left me on disability. Am trying to get back into
the loop, just to stay mentally limber if for no other reason. Also fix
things for family and friends on occasion.

Current understanding: I am thinking that if I can plot the load line for
the transistor in question and determine the Q-point, I will be halfway
there. Am just wondering if there is anything else I should do before
setting down at the workstation.

The reason for all of this is, I live in a house with steal siding that
shields my whip antenna from all but the most powerful broadcasts under 30
MHz. Am wanting to be able to pick up Voice of Korea without an outside
antenna, from my bedroom. Not easy. Have already built the basic project,
but it doesn't work as well as I think it should. Trying to improve it.

That's the basic blurb. Didn't get scared away, just impressed with all
there is to know and understand. Sorry it took me so long to reply.
Holiday busyness, and my disability got in the way. Can upload the entire
scematic to abse, if anyone really cares. It's still in transition though.

Thanks, all, for your input. I am busy chasing down ideas now.

Dave

 

[Dave]

PS: Merry Christmas, everybody.


"Dave" <db5151@hotmail.com> wrote in message
news:YfudnRVDjcT8bK7WnZ2dnUVZ_tidnZ2d@posted.internetamerica...

"pimpom" <pimpom@invalid.invalid> wrote in message
news:hh0g2n$mth$1@news.albasani.net...
Jon Kirwan wrote:
On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a bipolar
transistor, while it's still all on paper? There must be a way, I
just don't know what it is, and am thinking that it's not necessary
to build the damn thing every time to *see* if it works.


But without knowing much about the OP or what problem is being worked,
it's really hard to know what to suggest. And the OP has remained
silent on this. Oh, well.


Perhaps I scared him off with my earlier reply, saying that certain
criteria should first be defined to make the term "optimum" meaningful,
while citing several examples of such criteria. If that's the case, it
was not my intention.


Hey pimpom,

No no, not scared, off, trying to get a handle on all that was mentioned
for thorough understanding and application of such. Still working on it,
as I only have a little time each day to work on this.

What I am trying to do: build a "hearing aid" for my shortwave radio,
essentially an RF amplifier that I can tune, which will filter out most
of the crap surrounding the station of interest, before feeding the output
to my Sony ICF 7600 for further cleanup/amplification. Originally tried
working with JFETs, but gave up on that when I found they don't really
offer any greater amplification than bipolars. Finally settled on the
NTE199 (and I don't know what that replaces) due to it's minimum 400Hfe.
Am thinking three of these in series would probably suffice for what I am
wanting. Found a biasing tutorial at
www.hobbyprojects.com/junction_transistors/biasing_a_transistor.html
(think I have that right,)which looks helpful, and am fiddling with it at
the moment. Also hitting the books again, so I can understand what it is
I am trying to do (Electronic Principles-Malvino and Art of
Electronics-Horowitz & Hill, 2nd ed).

My background: Taught myself the fundamentals of electronics in high
school (30+ years ago) and went to a trade school to get a better
understanding of such. Worked on peripheral computer equipment in a
mainframe environment and than in a mini-system/small business environment
for 12 years before auto-accident/head injury left me on disability. Am
trying to get back into the loop, just to stay mentally limber if for no
other reason. Also fix things for family and friends on occasion.

Current understanding: I am thinking that if I can plot the load line for
the transistor in question and determine the Q-point, I will be halfway
there. Am just wondering if there is anything else I should do before
setting down at the workstation.

The reason for all of this is, I live in a house with steal siding that
shields my whip antenna from all but the most powerful broadcasts under 30
MHz. Am wanting to be able to pick up Voice of Korea without an outside
antenna, from my bedroom. Not easy. Have already built the basic
project, but it doesn't work as well as I think it should. Trying to
improve it.

That's the basic blurb. Didn't get scared away, just impressed with all
there is to know and understand. Sorry it took me so long to reply.
Holiday busyness, and my disability got in the way. Can upload the entire
scematic to abse, if anyone really cares. It's still in transition
though.

Thanks, all, for your input. I am busy chasing down ideas now.

Dave

 

[pimpom]

Dave wrote:

"pimpom" <pimpom@invalid.invalid> wrote in message
news:hh0g2n$mth$1@news.albasani.net...
Jon Kirwan wrote:
On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a
bipolar transistor, while it's still all on paper? There
must be
a way, I just don't know what it is, and am thinking that
it's
not necessary to build the damn thing every time to *see*
if it
works.

But without knowing much about the OP or what problem is
being
worked, it's really hard to know what to suggest. And the OP
has
remained silent on this. Oh, well.


Perhaps I scared him off with my earlier reply, saying that
certain
criteria should first be defined to make the term "optimum"
meaningful, while citing several examples of such criteria. If
that's the case, it was not my intention.


Hey pimpom,

No no, not scared, off, trying to get a handle on all that was
mentioned for thorough understanding and application of such.
Still
working on it, as I only have a little time each day to work on
this.

What I am trying to do: build a "hearing aid" for my shortwave
radio,
essentially an RF amplifier that I can tune, which will filter
out
most of the crap surrounding the station of interest, before
feeding
the output to my Sony ICF 7600 for further
cleanup/amplification. Originally tried working with JFETs, but
gave up on that when I found
they don't really offer any greater amplification than
bipolars. Finally settled on the NTE199 (and I don't know what
that replaces)
due to it's minimum 400Hfe. Am thinking three of these in
series
would probably suffice for what I am wanting. Found a biasing
tutorial at
www.hobbyprojects.com/junction_transistors/biasing_a_transistor.html
(think I have that right,)which looks helpful, and am fiddling
with
it at the moment. Also hitting the books again, so I can
understand
what it is I am trying to do (Electronic Principles-Malvino and
Art
of Electronics-Horowitz & Hill, 2nd ed).
My background: Taught myself the fundamentals of electronics in
high
school (30+ years ago) and went to a trade school to get a
better
understanding of such. Worked on peripheral computer equipment
in a
mainframe environment and than in a mini-system/small business
environment for 12 years before auto-accident/head injury left
me on
disability. Am trying to get back into the loop, just to stay
mentally limber if for no other reason. Also fix things for
family
and friends on occasion.
Current understanding: I am thinking that if I can plot the
load line
for the transistor in question and determine the Q-point, I
will be
halfway there. Am just wondering if there is anything else I
should
do before setting down at the workstation.

The reason for all of this is, I live in a house with steal
siding
that shields my whip antenna from all but the most powerful
broadcasts under 30 MHz. Am wanting to be able to pick up
Voice of
Korea without an outside antenna, from my bedroom. Not easy.
Have
already built the basic project, but it doesn't work as well as
I
think it should. Trying to improve it.
That's the basic blurb. Didn't get scared away, just impressed
with
all there is to know and understand. Sorry it took me so long
to
reply. Holiday busyness, and my disability got in the way. Can
upload the entire scematic to abse, if anyone really cares.
It's
still in transition though.
Thanks, all, for your input. I am busy chasing down ideas now.

Dave

Some of us have trouble accessing binaries at abse. Perhaps you
could upload the schematic to a free image hosting site instead.
Imageshack is just one example of such a site.

 

[Dave]

"pimpom" <pimpom@invalid.invalid> wrote in message
news:hh1tfr$mom$1@news.albasani.net...

Dave wrote:
"pimpom" <pimpom@invalid.invalid> wrote in message
news:hh0g2n$mth$1@news.albasani.net...
Jon Kirwan wrote:
On Thu, 24 Dec 2009 16:19:28 GMT, "Kevin Aylward"
kaExtractThis@kevinaylward.co.uk> wrote:

Dave wrote:
How can one tell if one has the optimum setup for biasing a
bipolar transistor, while it's still all on paper? There must be
a way, I just don't know what it is, and am thinking that it's
not necessary to build the damn thing every time to *see* if it
works.

But without knowing much about the OP or what problem is being
worked, it's really hard to know what to suggest. And the OP has
remained silent on this. Oh, well.


Perhaps I scared him off with my earlier reply, saying that certain
criteria should first be defined to make the term "optimum"
meaningful, while citing several examples of such criteria. If
that's the case, it was not my intention.


Hey pimpom,

No no, not scared, off, trying to get a handle on all that was
mentioned for thorough understanding and application of such. Still
working on it, as I only have a little time each day to work on this.

What I am trying to do: build a "hearing aid" for my shortwave radio,
essentially an RF amplifier that I can tune, which will filter out
most of the crap surrounding the station of interest, before feeding
the output to my Sony ICF 7600 for further cleanup/amplification.
Originally tried working with JFETs, but gave up on that when I found
they don't really offer any greater amplification than bipolars. Finally
settled on the NTE199 (and I don't know what that replaces)
due to it's minimum 400Hfe. Am thinking three of these in series
would probably suffice for what I am wanting. Found a biasing
tutorial at
www.hobbyprojects.com/junction_transistors/biasing_a_transistor.html
(think I have that right,)which looks helpful, and am fiddling with
it at the moment. Also hitting the books again, so I can understand
what it is I am trying to do (Electronic Principles-Malvino and Art
of Electronics-Horowitz & Hill, 2nd ed).
My background: Taught myself the fundamentals of electronics in high
school (30+ years ago) and went to a trade school to get a better
understanding of such. Worked on peripheral computer equipment in a
mainframe environment and than in a mini-system/small business
environment for 12 years before auto-accident/head injury left me on
disability. Am trying to get back into the loop, just to stay
mentally limber if for no other reason. Also fix things for family
and friends on occasion.
Current understanding: I am thinking that if I can plot the load line
for the transistor in question and determine the Q-point, I will be
halfway there. Am just wondering if there is anything else I should
do before setting down at the workstation.

The reason for all of this is, I live in a house with steal siding
that shields my whip antenna from all but the most powerful
broadcasts under 30 MHz. Am wanting to be able to pick up Voice of
Korea without an outside antenna, from my bedroom. Not easy. Have
already built the basic project, but it doesn't work as well as I
think it should. Trying to improve it.
That's the basic blurb. Didn't get scared away, just impressed with
all there is to know and understand. Sorry it took me so long to
reply. Holiday busyness, and my disability got in the way. Can
upload the entire scematic to abse, if anyone really cares. It's
still in transition though.
Thanks, all, for your input. I am busy chasing down ideas now.

Dave

Some of us have trouble accessing binaries at abse. Perhaps you could
upload the schematic to a free image hosting site instead. Imageshack is
just one example of such a site.

Ah. Noted. If anyone wants it, will put it there. Have to check that out.

Thank you.

Dave