Various Transistors Tested for Ic and Vce(sat)

[Watson A.Name - Watt Sun, Dark Remover]

On Sun, 4 Jan 2004 08:57:28 -0800, Watson A.Name - "Watt Sun, Dark

[snip]
I was just trying to introduce the concept of "analysis" into circuits
of this sort.

Watson has hung his hat on VCE(sat) and that's only a small portion of
the variability he's observing.

I am certain that Watson, and most lurkers here, *cannot* analyze
(i.e. predict performance in advance of building) this circuit.

Fred Bloggs: Please hold your tongue so that I can incite some
thinking... if you simply spit out the answer all my attempts at
teaching people to think will be lost.

...Jim Thompson

I don't have a SPICE prog. Like Steve Ciarcia says, my favorite
programming language is solder.

Hey the thing's sitting there, working. For the inductor, I used a
Mouser #580-22R104.

(1) I didn't have in mind using Spice. Use pencil and paper.
Remember that stuff?

(2) What is the definition of "working"... as you *predicted* before
building it, or that it just happens to light the LED ?

Of course I use 'pencil and paper', or more like a calculator and
computer. I see this schematic posted here,
http://home.comcast.net/~rcmonsen/misc/ledtorch.jpg
I looked at R3 and said, well, there's a volt and a half minus a B-E
drop, or about .9V across the resistor. In order to get a hundred mA
thru Q2, say with a forced beta of 30, which is what the graphs for
2SD965 show, the base current has to be at least 3 mA. Well, with a
1k for R3, it's _not_ gonna happen! So I figure at the highest, it
should be 330 ohms. And I work from there.

Is that pencil and paper?

...Jim Thompson

What does "forced beta" mean? Seriously! It's a rule-of-thumb... not
a reality! Revert to fundamentals, stop guessing, otherwise you'll
always be a hacker.

...Jim Thompson

As for a hacker, I seriously hope so. After seeing what you guys are
saying in the other Spice thread, better you than me.

Forced beta? As I said in the other followup, as the transistor goes
into saturation, the base to collector junction becomes forward
biased, and the beta is reduced as more of the base current gets
diverted to the collector.

Revert to fundamentals? Well, what am I doing above when I put pencil
to paper? Isn't that fundamentals? Seriously! Guessing at what?



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Watson A.Name - Watt Sun, Dark Remover]

[email protected] mentioned... [snip]

The purpose of asking for the data-taking was to cause your mind to do
a little correlation and then some further thought ;-)

For instance... what *is* saturation and what determines when a
transistor will come out of saturation?

...Jim Thompson

IIRC, saturation is the point where Ic has reached its maximum value,
and further increases in Ib won't increase Ic.

^^^^^^^^^^^^^^^^^
CAN'T increase collector current due to OTHER circuit restraints.

Re-evaluate your statement for the case of VCE = 10V, for instance.

For what current? There has to be some limit to the current, like a
load resistor, or the transistor will 'let the smoke out' as some hav
fondly put it.

Actually more *base* current "leaks" into the collector, killing the
base drive.


That is a correct statement.

Congrats! I'm patting myself on the back. I put my hand on the copy
machine, made a copy, thumbtacked it to the wall, and now I can lean
up against it!

...Jim Thompson

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Watson A.Name - Watt Sun, Dark Remover]

[email protected] mentioned... [snip]

You are the first person to note that the device comes out of
saturation based upon *BETA*! *NOT* the saturation rating of the
transistor!

Congratulations!

I tried to give Watson some measurement hints, but he ignored them,
citing Electronic Design as the "authority"... ROTFLMAO!

Authority? These were submitted to them by readers, ElecDesign had
little to do with them. That's why I put the smiley in there.

ISTR that the editor glowingly endorsed the "design".

When Vce(sat) at higher currents is low, it minimizes the amount of
power wasted in the transistor. Better efficiency.

I've said that transistors like the 2N3904 don't have good beta holdup
at higher currents. The 2N4401, BC338, and ZTX651 have increasing
beta holdups at higher currents.

You are *wrong* in using the term "beta holdup at higher current".
But if you had said the 2N3904 has a lower beta than the ZTX651 you
would have been correct.

...Jim Thompson

"the 2N3904 has a lower beta than the ZTX651" at a given current. I
assume that at some small current, maybe less than a mA, the ZTX651
has lower beta than the 2N3904. IIRC the data sheets use beta holdup.
I assume that this term is used to mean that the beta doesn't drop off
as quickly as current increases. But the beta tends to peak at some
optimum point depending on the transistor.



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Jim Thompson]

[email protected] mentioned... [snip]

You are *wrong* in using the term "beta holdup at higher current".
But if you had said the 2N3904 has a lower beta than the ZTX651 you
would have been correct.

...Jim Thompson

"the 2N3904 has a lower beta than the ZTX651" at a given current. I
assume that at some small current, maybe less than a mA, the ZTX651
has lower beta than the 2N3904. IIRC the data sheets use beta holdup.
I assume that this term is used to mean that the beta doesn't drop off
as quickly as current increases. But the beta tends to peak at some
optimum point depending on the transistor.

The ZTX651 has slower drop in beta versus current since it is
physically larger and less subject to current crowding out to the edge
of the emitter.

You would expect that the ZTX651 beta *would* be lower than the 2N3904
at low currents, but the model says no.

Since this fall-off at low currents is leakage-related, I would guess
that the ZTX651 has a higher voltage rating? (I don't have a data
sheet available.)

...Jim Thompson

 

[Jim Thompson]

[email protected] mentioned... [snip]
The purpose of asking for the data-taking was to cause your mind to do
a little correlation and then some further thought ;-)

For instance... what *is* saturation and what determines when a
transistor will come out of saturation?

...Jim Thompson

IIRC, saturation is the point where Ic has reached its maximum value,
and further increases in Ib won't increase Ic.

^^^^^^^^^^^^^^^^^
CAN'T increase collector current due to OTHER circuit restraints.

Re-evaluate your statement for the case of VCE = 10V, for instance.

For what current? There has to be some limit to the current, like a
load resistor, or the transistor will 'let the smoke out' as some hav
fondly put it.

Current crowding causes beta to fall, so there often is a limit before
"smoke".

Congrats! I'm patting myself on the back. I put my hand on the copy
machine, made a copy, thumbtacked it to the wall, and now I can lean
up against it!

LOL!

...Jim Thompson

 

[John Todd]

I object to "explanations" that don't fit the facts. So I will post
my objections, and correct the explanations, so that those lurkers
wishing to learn can do so.

And thank you very much for that.

Actually, I prefer a world where virtually no one understands *why*
things work... keeps me employed ;-)

Unfortunately, when people don't understand what I do, they
seem less willing to pay for it!

 

[Jim Thompson]

And thank you very much for that.


Unfortunately, when people don't understand what I do, they
seem less willing to pay for it!

Customers don't need to understand "why", just that it works and
passes worst-case analysis.

...Jim Thompson

 

[John Woodgate]

I read in alt.binaries.schematics.electronic that Jim Thompson
4ax.com>) about 'Various Transistors Tested for Ic and Vce(sat)', on
Wed, 7 Jan 2004:

[snip]

Actually, I prefer a world where virtually no one understands *why*
things work... keeps me employed ;-)

Unfortunately, when people don't understand what I do, they
seem less willing to pay for it!

Customers don't need to understand "why", just that it works and
passes worst-case analysis.

H'mm. My experience is the same a John Todd's. You HAVE to give an
explanation. It may be that it doesn't apply to the insides of ICs; they
may be deemed 'magic'.

 

[Jim Thompson]

I read in alt.binaries.schematics.electronic that Jim Thompson
4ax.com>) about 'Various Transistors Tested for Ic and Vce(sat)', on
Wed, 7 Jan 2004:

On Tue, 06 Jan 2004 12:21:05 -0700, Jim Thompson
[snip]

Actually, I prefer a world where virtually no one understands *why*
things work... keeps me employed ;-)


Unfortunately, when people don't understand what I do, they
seem less willing to pay for it!

Customers don't need to understand "why", just that it works and
passes worst-case analysis.

H'mm. My experience is the same a John Todd's. You HAVE to give an
explanation. It may be that it doesn't apply to the insides of ICs; they
may be deemed 'magic'.

Yep, Particularly when I tell 'em it's all done with mirrors ;-)

...Jim Thompson

 

[Watson A.Name - Watt Sun, Dark Remover]

I have posted BetaCurves.pdf on the S.E.D/Schematics page of my
website.

I have run beta (DC, beta=IC/IB) curves for the four transistors that
Watson tried in his (yet another LED driver.

I show beta curves versus current for various VCE conditions.

Hope this is useful.

...Jim Thompson

All the BC338s I've measured for beta have betas of typically 300 to
400, and at least 240. So if they were used in your example chart,
the blue line would be at the very top, or off the chart.



--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@

 

[Greg Pierce]

[email protected] mentioned... [snip]

You are *wrong* in using the term "beta holdup at higher current". But
if you had said the 2N3904 has a lower beta than the ZTX651 you would
have been correct.

...Jim Thompson

"the 2N3904 has a lower beta than the ZTX651" at a given current. I
assume that at some small current, maybe less than a mA, the ZTX651 has
lower beta than the 2N3904. IIRC the data sheets use beta holdup. I
assume that this term is used to mean that the beta doesn't drop off as
quickly as current increases. But the beta tends to peak at some
optimum point depending on the transistor.

The ZTX651 has slower drop in beta versus current since it is physically
larger and less subject to current crowding out to the edge of the
emitter.

You would expect that the ZTX651 beta *would* be lower than the 2N3904 at
low currents, but the model says no.

Since this fall-off at low currents is leakage-related, I would guess that
the ZTX651 has a higher voltage rating? (I don't have a data sheet
available.)

Allow me:
http://www.zetex.com/3.0/pdf/ZTX650.pdf

 

[Watson A.Name - Watt Sun, Dark Remover]

[email protected] mentioned... [snip]

You are *wrong* in using the term "beta holdup at higher current".
But if you had said the 2N3904 has a lower beta than the ZTX651 you
would have been correct.

...Jim Thompson

"the 2N3904 has a lower beta than the ZTX651" at a given current. I
assume that at some small current, maybe less than a mA, the ZTX651
has lower beta than the 2N3904. IIRC the data sheets use beta holdup.
I assume that this term is used to mean that the beta doesn't drop off
as quickly as current increases. But the beta tends to peak at some
optimum point depending on the transistor.

The ZTX651 has slower drop in beta versus current since it is
physically larger and less subject to current crowding out to the edge
of the emitter.

Using the National die specs as a reference, the 2N3904 has a die size
of 13 by 13 mils, or 169 square mils. In contrast, the 2N4401 has a
die of 18 by 18 mils or a 324 square mils, almost double the area.
So it seems that size does matter.

You would expect that the ZTX651 beta *would* be lower than the 2N3904
at low currents, but the model says no.

The model? Does Zetex publish this, or is it something from a
supposedly "authoritative source"? But then why should I care, since
I'm using the real thing, not tne model.

Since this fall-off at low currents is leakage-related, I would guess
that the ZTX651 has a higher voltage rating? (I don't have a data
sheet available.)

Seems that the more-than-1A transistors usually have a low Vceo, but
the ZTX651 is not as low as the others.

Data sheet at http://www.dialelec.com/823.html and take the lame
reverse Turing Test, etc.

...Jim Thompson

--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@