an electronish puzzle

someone down again" stories...pathetic.

Your Pollyanna self-adornment IS becoming sickingly sweet ;-)

...Jim Thompson

Silicon junctions in breakdown DO light up... I know from unfortunate experience :-(

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Good point. "Can be" is hypothetical and conditional. "[T]he resident idiots" is an "If the shoe fits, wear it." kind of thing. It could refer to the empty set, ideally.

I will try to avoid more name calling.

I don't remember having any trouble with our transistor-as-reference zener things. I recall running them at a couple mA, which was the tc sweet spot. I think they were the old GE things in the funny cylinder+halfpipe package with the concave top. Maybe they were klunky geometries, big junctions or something.

GE did make a wonderful monolithic back-to-back zener in the same package. It made a good reference, and was great as a symmetric clamp in opamp circuits. D13T1, H11F1, something like that. They also made "reference amplifiers" which were transistors with zeners in the emitters; they were outrageously stable, and Fluke used them as the ref in their later differential voltmeters.

John

It's easy to google; you get stuff like...

I've seen some very pretty microphotographs of the light somewhere.

John

Oh God! How will I ever live this down? My NG credibility lies in ruins. Fred will use this against me for years to come.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

....

At this point, I think Pease would be mistaken in that suggestion. (Still willing to be educated, however.) I have not found that article, so he may well have been referring to the effect in the paper you pointed out rather than the one in the puzzle. More later.

Thanks a bunch. (And thanks for not sending me to that "Somebody wants you to use Google" site!)

As that paper makes clear, it is avalanche breakdown that produces the carriers that can recombine (and sometime emit) to create that light. Since avalanche produces carriers of both kinds (majority/minority), it is distinctly different from zener breakdown, where only minority carriers tunnel and become majority carriers. So my skepticism remains regarding the emission of light due to a zenering b-e junction.

I wonder where it comes out.

Well, the base is back-biased until it conducts, and light comes out. If you want to be picky about avalanche-v-zener, go for it.

Pics I've seen, it was a thin closed path, twisty ring sort of thing, that corresponded to the edges of the base diffusion. Very pretty.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Well, I am picky. Sometimes even when it matters. As I wrote earlier, I do not think "zenering" creates the same kind of carriers as avalanching, and that the majority carriers from "zenering" (tunnelling) are not going to produce that light emission.

Maybe I did not make this quite clear in the puzzle question, but when I stated "a BJT of the usual sort, having a low emitter-base reverse breakdown voltage", tunnelling is at least indicated. (And to the extent it is ambigous, an issue for discussion or assumption.)

Larry Brasfield wrote: > "Fred Bloggs" wrote in > message news: snipped-for-privacy@nospam.com... >

Everything you say has been proven to be a lot of hot air and bs so far- you have no credibility here- so you can go to hell. This will be one place about which you will *never* be able to make up one of your bs ego-nut stories about turning anyone around to recognize your great genius. You are a sorry sack of sh_t.

Actually no, I tried it as a way to get a higher voltage zener. If you look just at the symbol, you'd get the impression it would work. If you think about the actual silicon, you'll see the 4 layered device.

I don't need one. The bench supply makes enough noise on its own.

Having a fun discussion.

Calling people names.

Please pick one.

OK. Stuck in the lab, tweaking the tempco of a 50 MHz LC oscillator (+125 ppm/k uncompensated), means I have time to kill. Lots of waiting involved. So I tried it.

Fairchild 2N4400 fresh from the stock room (3 cents each). +10 on the collector, base grounded, emitter to a power supply, all currents measured.

At zero on the emitter supply, Ic is about 9 na; that's what you get for 3 cents, I suppose. As Ve is pulled up, nothing happens until the emitter zeners (or avalanches, whatever) and then Ic starts to

It's apparently linear up to Ie of 10 mA, all i did, at which time Ic is up to 260 nA. The effective beta in this mode is then 2.6e-5.

So, why can't a poor engineer buy NTC surface mount ceramic capacitors anywhere? That's the real mystery.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Neat.

I trust there was some real resistor limiting the base-emitter breakdown current. I'm not sure what would happen at "heat the part" levels. And one of the fun parts of the question, (one of those 2nd order effects I did not mention), is that the collector-base leakage *should* go up as you elevate that junction temperature, a result sure to follow from your X current at the 6 to 8 V defined by the base.

Also, the theory I offered did depend on tunnelling at the emitter-base. I have never known whether all transistors zener there, or whether some do and others avalanche instead. That is why there is the surely vague "a low emitter-base reverse breakdown voltage". (Remember, this was an interview question.) If the part you have is going into avalanche, there should be a collector current increase because some minority carriers manage to diffuse away from the avalanche region, (at its edges). (The ones that do not go the other way or turn into light.)

Do you have any RF transistors? (The kind with the *really* low base-emitter breakdown voltage? ;-) Those are much more likely to do zener mode.

It would be interesting to pulse the breakdown current and see the short term response that is not so influenced by junction temperature rises.

(Not trying to be cute, just a tip if needed ...) Aren't they called COG or NPO now? Try:

Oh, please.

The numbers don't look like heating to me.

So, all sorts of guys didn't get hired because you expected them to tell you something about transistors that's actually not true.

Tons.

Sounds like real work.

C0G/NP0 are close to zero TC. What is need is a net circuit capacitance with a TC in the -250 PPM/K range, to compensate the inductor, mostly. Most people want an order for hundreds of thousands before they'll run off a batch.

Maybe these guys:

John

(Mostly a technical post)

Please, John. I expected so, but you know what they say about spelling "assume". For all I knew, you limited the current in some other way.

With the temperature sensitivity of thermal generation in Si, (about 3x per 10 oC), it would only take about a 30 oC temperature rise to get the result you saw at

No, that is definitely not what happened. If that was the way I operated, my managers should have been fired for letting me do interviews at all.

My distinction between "posers" and "knowers" is not the ego game some might imagine. Anybody who does interviews and reads resumes knows that they often are greatly exaggerated. One of my tasks has long been to attempt to guage the degree of such exaggeration.

There is real use for some ambiguities in interview questions. The interviewee gets a chance to see them and either ask a clarifying question, state his/her assumption(s) when answering, or field a question about it otherwise with the opportunity to then show how they manage the problem of error, however slight or serious it may be.

The purpose is to quickly evaluate a potential hire, not to give her/him a pass/fail, or to "win".

As for the "actually not true", that is not clear for a couple reasons already suggested. (And it is largely beside the point for the interview. I have often been educated by interviewees.)

You wrote earlier: It's apparently linear up to Ie of 10 mA, all i did, at which time Ic is up to 260 nA. If it was not exponential, as the temperature effect would cause, then either your transistor is going into avalanche or the mechanism at work is one which has eluded everybody here (who played), including myself, along with a number of bright interviewees including one with a PhD obtained after his work in novel semiconductor devices. I will soon be asking him again about this puzzle. For all I know, there could be another, parallel effect in addition to all the tunneling.

Your numbers certainly suggest that only a small fraction of the carriers injected are minority ones. What you are seeing could well be one of the 2nd order effects, beating out the one I mentioned. As I have never attempted to quantify them, I am not prepared to say that the 1st order one has been at all disproved, even if your transistor was zenering. As I mentioned, the reduction of minority carriers in the base region is a pretty small effect, so one should not be surprised if it is surpassed by one or more of the other small effects.

That is a *lot* of transistors! So, can you get interested in plugging one into your setup? (I should assume not at this point, I guess.)

Sounded like an interesting experiment.

Another interesting experiment is to reverse the transistor, (adjusting the 10V down, of course), and breakdown the collector, while measuring emitter current. That *will* be an avalanche scenario.

(Blush.) I had completely forgotten about NTCs and that characteristic. I have never used one, and can but dimly remember classifying them as a curiosity made for dialing-tone circuits or some such niche. If you are a score-keeper, take a point (or as many as you like). (Or keep it/them with my "forced" concurrance. ;-)

Has anybody ever tried to build inductors with very low TC? It seems that if the meter could be a piece of metal for awhile, it should be possible to make a stable coil. (Or is that TC perfectly compensating one of the ferrites?)

Good luck finding it.