VBC of npn transistor in common collector mode

[John B]

"Rich Grise"

Granted.

I can't imagine a beta less than one, but I haven't really looked at
upside-down transistor circuits all that much.


This one, I don't know - why not slap one in the protoboard, and tell us?

Cheers!
Rich

Thanks for the reply.

I have read every entry in this thread, since I am the OP. Elsewhere, I
stated that I have observed textbook information on the 2N3903 transistor,
specifically, graphical information yielding beta. BF=117, but BR= 0.9.

Another poster offered that V BC (in a common-emitter, inverted topology)
was not much different from V BE (in a common-emitter topology).

Another poster emphasized that the saturation voltage of an inverted
transistor was lower than the saturation voltage of an uninverted
transistor. Specifics were absent. I am not convinced.

I was hoping to see a very low V BC. I'll try this on a bench, at some
point in the next couple of weeks. I learned more from this thread, though.

 

[John Larkin]

What font was that in? It doesn't line up, and the bottom line wraps!

Courier, or Courier New, is a pretty standard fixed-width font I can
recommend.

Tim

Yeah, I write all my manuals in Courier New, and they are bright and
clear and everything lines up. Then the Powers That Be take them and
reformat into Times New Roman and then they look like hell.

John

 

[Jim Thompson]

Yeah, I write all my manuals in Courier New, and they are bright and
clear and everything lines up. Then the Powers That Be take them and
reformat into Times New Roman and then they look like hell.

John

I prefer Arial/Helvetica myself, justified left AND right.

Of course I do my illustrations with the appropriate graphics program,
NOT with ASCII crap ;-)

...Jim Thompson

 

[John Larkin]

I prefer Arial/Helvetica myself, justified left AND right.

Of course I do my illustrations with the appropriate graphics program,
NOT with ASCII crap ;-)

...Jim Thompson

I give my doodles to my drafting guy, and he does them in Autocad and
exports gif's for figures in manuals.

I wouldn't mind learning a nice line-drawing package, if anybody can
recommend one.

John

 

[Terry Given]

"Rich Grise"


Thanks for the reply.

I have read every entry in this thread, since I am the OP. Elsewhere, I
stated that I have observed textbook information on the 2N3903 transistor,
specifically, graphical information yielding beta. BF=117, but BR= 0.9.

Another poster offered that V BC (in a common-emitter, inverted topology)
was not much different from V BE (in a common-emitter topology).

Another poster emphasized that the saturation voltage of an inverted
transistor was lower than the saturation voltage of an uninverted
transistor. Specifics were absent. I am not convinced.

I was hoping to see a very low V BC. I'll try this on a bench, at some
point in the next couple of weeks. I learned more from this thread, though.

Did you download the PDF from Jims website? its very informative.

FWIW I once accidentally built an inverted CE BJT into a product - the
CAD guy flipped the SOT23 (BC847 IIRC). and it still worked. the sw guy
noticed something odd, which I promptly ignored (guess what - I dont do
that any more. If something looks funny, I now measure the amount of
funny and figure out why). 5 months later we did immunity tests, and it
failed - BJT had bugger all reverse beta, and couldnt win the pissing
match against a coupling clamp. so we wrote a program that analysed the
PCB file, looking for flipped parts.

Cheers
Terry

 

[Eeyore]

FWIW I once accidentally built an inverted CE BJT into a product - the
CAD guy flipped the SOT23 (BC847 IIRC). and it still worked. the sw guy
noticed something odd, which I promptly ignored

LOL !

I once 'flipped' an HC something or other ( bus interface ) in Orcad and forgot,
and got the ins and outs the wrong way round. It must have been a transparent
latch I think. That caused a few hiccups for the s/w guy but he knows his hardware
too and twigged it ! Just needed one leg pulled up and a bit of patch wire to get
it working perfectly of course.

Graham

 

[YD]

LOL !

I once 'flipped' an HC something or other ( bus interface ) in Orcad and forgot,
and got the ins and outs the wrong way round. It must have been a transparent
latch I think. That caused a few hiccups for the s/w guy but he knows his hardware
too and twigged it ! Just needed one leg pulled up and a bit of patch wire to get
it working perfectly of course.

Graham

I once designed a board with half a dozen BC548s as relay drivers.
None of them worked, though we could measure a voltage drop and they
did get slightly warm. It took a couple of hours to realize that they
were OK, except that C and E were inverted from the normal pinout.

- YD.

 

[RST Engineering \(jw\)]

The easiest one I've ever used is Ashlar's DrawingBoard, followed closely by
Autodesk's Autosketch -- both less than $100. Sadly, they are both off the
market, probably because they were cutting in to the pricey product sales.

I'm looking for a bonehead simple freebie that I can give out to my students
who are just like you and I -- they have absolutely no interest in becoming
cadastrial delineators but just need to draw boxes and circles for prototype
fabrication. If you come across one, please let me know. Most of the
freebies I've found are come-ons for the high priced spread and kill
themselves after a short trial period.

Jim

 

[John Popelish]

The easiest one I've ever used is Ashlar's DrawingBoard, followed closely by
Autodesk's Autosketch -- both less than $100. Sadly, they are both off the
market, probably because they were cutting in to the pricey product sales.

I'm looking for a bonehead simple freebie that I can give out to my students
who are just like you and I -- they have absolutely no interest in becoming
cadastrial delineators but just need to draw boxes and circles for prototype
fabrication. If you come across one, please let me know. Most of the
freebies I've found are come-ons for the high priced spread and kill
themselves after a short trial period.

The most intuitive drafting program I used is called Draft Choice for
Windows by Trius. It is fairly primitive, but very easy to use and
old shareware (now discontinued). But you can still find copies on
the net:
ftp://ftp.externet.hu/pub/mirror/sac/graph/dcwin2i.zip

It has all you need for simple mechanical drawings, but you can build
symbol libraries to do things like schematics. I have one of these I
use a lot.

 

[RST Engineering \(jw\)]

It also is not shareware and expires after 30 days.

Jim

 

[John Popelish]

It also is not shareware and expires after 30 days.

Mine didn't expire, it just scolded me for not paying for it, after 30
days. After several years, I decided I had done enough productive
work with it to pay the $60 or whatever to get rid of the nag. Then
they dropped support for it.

 

[YD]

Mine didn't expire, it just scolded me for not paying for it, after 30
days. After several years, I decided I had done enough productive
work with it to pay the $60 or whatever to get rid of the nag. Then
they dropped support for it.

If it's gone abandonware [*] surf over to www.astalavista.box.sk and
dig out a serial. Be aware that many of the linked sites are scams
loaded with porn. Turn off java and javascript. Avoid using IE unless
security settings are at totally paranoid.

I use it myself for instrumentation diagrams. Then export them as DXF
so the autocad guy can get them into the central database.

[*] Not sold nor supported for several years.

- YD.

 

[joseph2k]

The easiest one I've ever used is Ashlar's DrawingBoard, followed closely by
Autodesk's Autosketch -- both less than $100. Sadly, they are both off the
market, probably because they were cutting in to the pricey product sales.

I'm looking for a bonehead simple freebie that I can give out to my students
who are just like you and I -- they have absolutely no interest in becoming
cadastrial delineators but just need to draw boxes and circles for prototype
fabrication. If you come across one, please let me know. Most of the
freebies I've found are come-ons for the high priced spread and kill
themselves after a short trial period.

Jim

PuhLeez, do not cry until you have tried a search engine and some of the
products you find that way.