Hi Everybody,
I recently received an email from a reader suggesting a change to the chapter on bipolar junction transistors, citing a comment by Douglas Self on transistor theory: namely that BJT's are actually voltage-controlled devices and not current-controlled. Here is the email in its entirety:
<email>
Hi Tony,
I had a quick look at your chapter on bipolar transistors and was
very disappointed that you are perpetuating the misleading myth that
transistors are current controlled devices - they are not! You are
doing a disservice to education.
A transistor is governed by the transistor equation that states that
Ic is a function of Vbe. The fact that this equation holds for many
decades of current should raise confidence that this is the actual
governing equation.
The fact that the collector and base currents differ by hfe (which
varies a lot due to many factors) is merely a SIDE-EFFECT of
transistor operation, it is not the BASIS of operation. Any design
based on hfe is a bad design!
I agree with Douglas Self's comments
(http://www.dself.dsl.pipex.com/ampins/discrete/discrete.htm):
"There is one thing to get straight first. The transistor is a
voltage-operated device. What counts is the base-emitter voltage, or
Vbe. Certainly a BJT needs base current to flow for it to operate, but
this is really an annoying imperfection rather than the basis of
operation. I appreciate this may take some digesting; far too many
textbooks say something like "a small current flowing into the base
controls a much larger current flowing into the collector". There is
no prize for locating the source of this quotation. In fact the only
truly current-operated amplifying device that comes to mind is the
Hall-effect multiplier, and you don't come across those every day.
I've certainly never seen one."
[I think Horowitz and Hill are the originators of this quotation!]
Please rethink how you teach this!
Best regards,
Fred.
</email>
This is an issue that crossed my radar after I had "handed the baton" to the capable folks at AllAboutCircuits, but I never pursued it further. Perhaps it is something to add to the "to do" list for future versions of the book.
Anyway, I'd like to say "thank you" to everyone participating in this project, especially Dennis Crunkilton. You have made my dream of an open-source, collaboratively-developed textbook a reality. Students at my college still use the book in its every-expanding form, and it stands as an example of the great things that can get done when motivated people pool their talents.
I've started a new textbook project, this one aimed at a more specialized field: industrial instrumentation and automation. You can find this work-in-progress at:
http://openbookproject.net/books/socratic/sinst/book/liii.pdf
This time I've used the Creative Commons "Attribution" license instead of the DSL to copyleft the work. The CC Attribution license is more liberal than the DSL, merely asking for proper attribution of credit if my new work is modified, extended, etc. This is the same CC license I've used on my "Socratic" teaching worksheets.
- Tony
P.S.
You might notice a different user name ("tony_kuphaldt" instead of "tonykuphaldt"). I lost my password to the old login, and the only email account recognized by the lost password utility was my ancient "liec0" Lycos account, which I've also lost the password for. So . . . I created a new account for these forums (and I'm saving this password in a safe place!). If the Admin needs to verify this, feel free to contact me at work:
Tony Kuphaldt -- Instructor, Instrumentation and Control Technology
Bellingham Technical College
3028 Lindbergh Avenue
Bellingham, WA 98225-1599
(360)-752-8477 [office]
(360)-752-7277 [fax]
tkuphald@btc.ctc.edu
I recently received an email from a reader suggesting a change to the chapter on bipolar junction transistors, citing a comment by Douglas Self on transistor theory: namely that BJT's are actually voltage-controlled devices and not current-controlled. Here is the email in its entirety:
<email>
Hi Tony,
I had a quick look at your chapter on bipolar transistors and was
very disappointed that you are perpetuating the misleading myth that
transistors are current controlled devices - they are not! You are
doing a disservice to education.
A transistor is governed by the transistor equation that states that
Ic is a function of Vbe. The fact that this equation holds for many
decades of current should raise confidence that this is the actual
governing equation.
The fact that the collector and base currents differ by hfe (which
varies a lot due to many factors) is merely a SIDE-EFFECT of
transistor operation, it is not the BASIS of operation. Any design
based on hfe is a bad design!
I agree with Douglas Self's comments
(http://www.dself.dsl.pipex.com/ampins/discrete/discrete.htm):
"There is one thing to get straight first. The transistor is a
voltage-operated device. What counts is the base-emitter voltage, or
Vbe. Certainly a BJT needs base current to flow for it to operate, but
this is really an annoying imperfection rather than the basis of
operation. I appreciate this may take some digesting; far too many
textbooks say something like "a small current flowing into the base
controls a much larger current flowing into the collector". There is
no prize for locating the source of this quotation. In fact the only
truly current-operated amplifying device that comes to mind is the
Hall-effect multiplier, and you don't come across those every day.
I've certainly never seen one."
[I think Horowitz and Hill are the originators of this quotation!]
Please rethink how you teach this!
Best regards,
Fred.
</email>
This is an issue that crossed my radar after I had "handed the baton" to the capable folks at AllAboutCircuits, but I never pursued it further. Perhaps it is something to add to the "to do" list for future versions of the book.
Anyway, I'd like to say "thank you" to everyone participating in this project, especially Dennis Crunkilton. You have made my dream of an open-source, collaboratively-developed textbook a reality. Students at my college still use the book in its every-expanding form, and it stands as an example of the great things that can get done when motivated people pool their talents.
I've started a new textbook project, this one aimed at a more specialized field: industrial instrumentation and automation. You can find this work-in-progress at:
http://openbookproject.net/books/socratic/sinst/book/liii.pdf
This time I've used the Creative Commons "Attribution" license instead of the DSL to copyleft the work. The CC Attribution license is more liberal than the DSL, merely asking for proper attribution of credit if my new work is modified, extended, etc. This is the same CC license I've used on my "Socratic" teaching worksheets.
- Tony
P.S.
You might notice a different user name ("tony_kuphaldt" instead of "tonykuphaldt"). I lost my password to the old login, and the only email account recognized by the lost password utility was my ancient "liec0" Lycos account, which I've also lost the password for. So . . . I created a new account for these forums (and I'm saving this password in a safe place!). If the Admin needs to verify this, feel free to contact me at work:
Tony Kuphaldt -- Instructor, Instrumentation and Control Technology
Bellingham Technical College
3028 Lindbergh Avenue
Bellingham, WA 98225-1599
(360)-752-8477 [office]
(360)-752-7277 [fax]
tkuphald@btc.ctc.edu