Say one takes an E-B junction of a transistor or other diode and measures the (reverse) breakdown voltage over a wide range of currents (say 5nA to 5mA), and assume there is no point or range where one sees characteristics of negative resistance or of oscillation. Also say that voltage is about 9 volts. Q: is that zener or avalanche breakdown? Q: how does one make a SPICE model of such a proposed beastie?
"Robert Baer"
** Start here:Do not pass GO, do not collect $200.
... Phil
At nine volts, the breakdown is by avalanche.
It happens in very small areas, and the transit times is picoseconds, so at low currents the avalanche self-extinguishes from time to time due to the statistical fluctuations in avalanche multiplication process - sometimes a charge carrier gets through the avalanche region without generating any new charge-carrier pairs.
This isn't easy to model in Spice - it probably needs a current- controlled random noise generator, but the real noise looks more like a series of Dirac spikes.
For added extra complexity, you can throw in the fact that the avalanche process generates light, and in glass-packaged zener diodes this can trigger other avalanches.
There was a thread on the subject here, many years ago - "Zener diode oscillation" from July 7, 1997.
-- Bill Sloman, Nijmegen
-- Bill Sloman, Nijmegen
For negative voltage I do think the voltage needs to be up around
12 volts. Min of 10.5 the last time I experimented with that.But this was all at the bench since LTspice can't sim that and I operated a LED flashing for quit some time to test if the beta was lose its punch.. It seem to survive the test.
And I did it with a 2n2222 if that makes any difference. I also noticed with a another batch of 2222's from a different SI maker, it would not work at all, unless the voltage range was different?
Jamie
Both phenomenon are present in any diode. Below ~5.6V breakdown is predominately Zener effect, above ~5.6V, predominately avalanche breakdown.
Accurately? Not easily. Spice has BV and IBV terms in the diode model. Some simulators, such as PSpice, support the Mextram BJT model which models avalanche in the _collector_:
Comes up as 404, but cross-references some links.
Off-the-top-of-my-head I don't know of a BJT model which covers the B-E junction during breakdown. Pasting a parallel diode with BV and IBV roughly covers the problem, but doesn't model the true effects that occur in the base region.
In much of the high-speed BJT (I/C) world, reverse-bias of the B-E junction is forbidden above ~2-4V due to it causing doping migration and ultimate device failure.
Here is what I use as a parameterized model for zeners that have no manufacturer's model...
**** .SUBCKT MyZENER 1 2 PARAMS: BV=10 IBV=1m RS=1 IS=10f CJO=10pF D1 1 2 DZ .MODEL DZ D(
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
At high temperatures it won't... ask my wife... her car was the testbench for early alternator regulator design ;-)
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
OK; the temperature coefficient is positive, so by WikiPedia "avalanche effect .. exhibits a positive temperature coefficient", as well as "above 5.6 volts, the avalanche effect becomes predominant". And that is exactly what i thought.. But.. I thought that diodes working in the avalanche region would NOT act in a monotonically increasing voltage VS current manner - especially over such a wide current range.
Looking under avalanche diodes, WikiPedia states "Avalanche diodes generate radio frequency noise. They are commonly used as noise sources in radio equipment and hardware random number generators. For instance, they are often used as a source of RF for antenna analyzer bridges. Avalanche diodes can also be used as white noise generators" which tends to support my confusion concerning the "actual" mode the diode is operating in.
The I-V curve indicates a zener mode, the negative TC indicates avalanche type (notice i avoided saying "mode").
So...i pete the questions again.
1) What about (say) 8.2 volts? 2) How would one go about accessing that 1997 thread?
As far as a given type (2N2222, 2N3904, etc etc & etc), every manufacturer of a given type will produce a transistor with different reverse E-B characteristics - and those characteristics can suddenly change with zero notice. Note the E-B breakdown is "off the data sheet"; lotta so-called quotes are "5V" and you will never find a (silicon small signal) transistor below 7V.
"Robert Baer"
** Yawnnnnnnnnnnnnnnnnnn....** You were expecting to see a tunnel diode effect ?
** Both statements are wrong.
FFS learn to read.
** Who cares.... Phil
Thanks for that model; will play with it. Which of those NXP BF?? transistors or diodes (big list i see) would be "closest" to the E-B of a 2N3904?
d
The cross-over point is around 4.7V IIRR - the temperature coefficient of the break-down voltage is the clue, because it is negative when the Zener mechanism is dominant, and postive when avalanche breakdown is dominant
Got to groups.google.com and click on "advanced search".
Searching on the exact phrase ""Zener diode oscillation" will do it.
-- Bill Sloman, Nijmegen
Best way to match E-B break-down equivalency is to match BVceo's. Any other differences are size-related rather than doping. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
It's even 'worse' than that. The noise changes 'character' as a function of current. Right near the 'knee' you go from random pulses to random steps. (random telegraph noise). With more noise at low frequency.... But I'm not sure it's 1/f.
And that room light can get in and 'modulate' the avalanche.
Yeah nice thread.
I find that for use as noise sources it's best to keep the current below the knee.
George H.
"Popcorn" noise... often seen in bipolar OpAmp input stages.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
and
ts
es
?Which isn't 1/f either, but probably reflects rather different physical process.
The random trapping and release of charge carriers at thin film interfaces or at defect sites in bulk semiconductor crystal could be happening in an avalanching diode, but people who talk about avalanche zener diodes as noise sources don't seem to find it necessary to invoke this particular mechanism.
-- Bill Sloman, Nijmegen
che=20
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n a=20
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nche=20
I'm guessing that Maturity wasn't on your New Year's resolution list.
Grow up.
mike
** No, you are - f****it.
FFS learn to read.
... Phil
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