Electronics > Projects, Designs, and Technical Stuff
Curve tracer designs?
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rhb:
No worries, mate.

https://www.tinaja.com/ebooks/TTLCB1.pdf

page 219
glue_ru:

--- Quote from: 0culus on November 18, 2018, 05:04:07 am ---
--- Quote from: JoeO on November 18, 2018, 03:00:56 am ---The schematic shows a 3M resistor while the parts list calls out a 2M resistor.

Have you tried them both?

--- End quote ---

Yeah, I tried 3Mohm too and it still doesn't work. There's 0.584 V on the base of the transistor and 6.160 V on the collector in that arrangement, and there is nothing at the emitter. Fairly sure the transistor isn't backwards.

--- End quote ---

would it help to add a schottky diode  to get better switching
rhb:

--- Quote from: 0culus on November 18, 2018, 05:04:07 am ---
--- Quote from: JoeO on November 18, 2018, 03:00:56 am ---The schematic shows a 3M resistor while the parts list calls out a 2M resistor.

Have you tried them both?

--- End quote ---

Yeah, I tried 3Mohm too and it still doesn't work. There's 0.584 V on the base of the transistor and 6.160 V on the collector in that arrangement, and there is nothing at the emitter. Fairly sure the transistor isn't backwards.

--- End quote ---

The voltage drop across the BC is lower than across the BE junction.  Forty years ago I built a bunch of very simple things using 2N2222s from Radio Shack, but none of them worked.  I went around asking everyone I knew how to identify the C & E leads.  No one knew.

As a break from looking through a microscope all day for my MS I attended an Electronics 101 class in the next building taught by a solid state physicist who had built a computer out of TTL logic just before the 8080, 6502 and such appeared.

One day he said, "The forward resistance across the base collector junction is lower than the forward resistance across the base emitter junction because the greater area of the collector exceeds the effect of the greater doping of the emitter."  All I had was an analog VOM, but sure enough, he was right and the reason nothing worked was the pinouts on the back of the package were wrong!

With modern DMMs you need to use the diode test function as the resistance ranges don't put out enough voltage to forward bias the junctions.
0culus:

--- Quote from: rhb on November 25, 2018, 12:33:52 am ---No worries, mate.

https://www.tinaja.com/ebooks/TTLCB1.pdf

page 219

--- End quote ---

Wow, that is very cool. Thanks! Saving that!


--- Quote from: rhb on November 25, 2018, 02:30:05 am ---
--- Quote from: 0culus on November 18, 2018, 05:04:07 am ---
--- Quote from: JoeO on November 18, 2018, 03:00:56 am ---The schematic shows a 3M resistor while the parts list calls out a 2M resistor.

Have you tried them both?

--- End quote ---

Yeah, I tried 3Mohm too and it still doesn't work. There's 0.584 V on the base of the transistor and 6.160 V on the collector in that arrangement, and there is nothing at the emitter. Fairly sure the transistor isn't backwards.

--- End quote ---

The voltage drop across the BC is lower than across the BE junction.  Forty years ago I built a bunch of very simple things using 2N2222s from Radio Shack, but none of them worked.  I went around asking everyone I knew how to identify the C & E leads.  No one knew.

As a break from looking through a microscope all day for my MS I attended an Electronics 101 class in the next building taught by a solid state physicist who had built a computer out of TTL logic just before the 8080, 6502 and such appeared.

One day he said, "The forward resistance across the base collector junction is lower than the forward resistance across the base emitter junction because the greater area of the collector exceeds the effect of the greater doping of the emitter."  All I had was an analog VOM, but sure enough, he was right and the reason nothing worked was the pinouts on the back of the package were wrong!

With modern DMMs you need to use the diode test function as the resistance ranges don't put out enough voltage to forward bias the junctions.

--- End quote ---

My Fluke 87V seems to have no trouble driving it in resistance mode; it would appear that I don't have the 2N3904 backwards by that heuristic. The base-collector is ~475k and the base-emitter is ~486k. In diode test mode, the base-collector is 0.707 V and the base-emitter is 0.712 V.
rhb:
Don wrote wonderful books.  There's an entire generation that acquired much of their knowledge of electronics from Don and a handful of other writers.  If you can explain it to a teenager, you *really* do know what you're talking about.

It took about a minute for me to find the circuit even though it is not indexed as a "staircase generator".  I knew it was in there, so I just had to think of synonyms.  I have been surprised at how often that's the book I grab off the shelf.  I read it so much I know what's there and I'm just checking that my memory is correct.

If you want to really be old school you can build it all from discretes.  Might have to.

BTW the "which is C and which is E" was my favorite question when I ran across someone who was *really* good at electronics.  No one was able to answer it until I ran across someone online a few years ago.  Fundamentally the difference between a scientist and an engineer.  Scientists rely on first principle and engineers on rote.  I feel pretty sure everyone I asked enjoyed the answer.  I *only* asked people who were "walks on water" good.  People like that enjoy such  little subtleties.  It is the pleasure derived from such things which made them good.
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