Transistors: Vbe Reverse Breakdown

RE: Transistors: Vbe Reverse Breakdown

mcb1 — Mon, 13 Feb 2017 08:35:38 GMT

Every time I hooked them up backwards, it was unintentional.

Usually the magic smoke exited left, so the gain was seriously changed.

Mark

RE: Transistors: Vbe Reverse Breakdown

D_Hersey — Mon, 13 Feb 2017 05:47:37 GMT

Ya got me there, noise generation is the only application I know of here. Regular Zener diodes have a structure called a 'guard ring' which diminishes the noise. There are two modes of breakdown in a reverse-biased diode, Zener and avalanche. Avalanche works at higher potentials and is marked by a charge carrier being likely to collide with another in the conduction channel. Zener conduction has the mean free path longer than the conduction channel. These modes are marked with a different signum of tempco, which was the hint to Clarence Melvin Zener that something was going on. As an aside we in Illinois are quite proud that CMZ worked at SIU. The breakdown of BE occurs at about the transition point between these regimes, 6.2 V. Thermal stabilization of Zener-based references is achieved through stacking with forward-biased diodes to balance the tempcos, see the Motorola Zener Diodes Handbook.

As noise sources these guys have a good signal amplitude but they need a fair amount of mathematical vetting. Two uncorrelated signals that are purely random sum as 1 + 1 = sqrt(2). Any even distribution of random numbers must 'come gray' after awhile.

http://www.noisecom.com/products/components/nc100-200-300-400-series-chips-and-diodes

http://www.rf-microwave.com/datasheets/6107_generic_NSG-10B_01.pdf

If you can deal with real low signal amplitudes you can get a scalable noise source you can use a thermionic generator

https://frank.pocnet.net/sheets/046/k/K81A.pdf These are for calibrating RF receivers which all have hella gain. Replace the antenna with the noise source and turn it up 'til the noise doubles then do the math. I needed a special GaAs HEMT amplifier to use this as a regular noise source. A relatively high-amplitude source can be made with a thyratron and a magnet, though IIRC it is a little less clean:

http://www.r-type.org/pdfs/6d4.pdf perhaps one could be made with a Geiger-Muller tube and a smoke detector

RE: Transistors: Vbe Reverse Breakdown

dougw — Sun, 12 Feb 2017 23:19:18 GMT

This transistor series has lots of interest. Thanks.

I have heard that the knee of the B-E reverse breakdown (although noisy) is sharper than a normal zener. But I have not tested this assertion.

Do you also get a similar reverse (but higher voltage) breakdown of the B-C junction?

RE: Transistors: Vbe Reverse Breakdown

Jan Cumps — Sun, 12 Feb 2017 21:04:37 GMT

Jon, how can you use it as a noise generator without the device destroying itself after some period of use?

RE: Transistors: Vbe Reverse Breakdown

jw0752 — Sun, 12 Feb 2017 20:24:09 GMT

Hi Jon,

I find your transistor series one of the most fascinating blog post series on the site. Thank you for continuing to shine some light on this subject which forms part of the foundation for all the more integrated electronics that we do.

John

RE: Transistors: Vbe Reverse Breakdown

DAB — Sun, 12 Feb 2017 19:37:04 GMT

Very interesting.

Now you have me curious about what is going on inside the semiconductor crystal matrix.

I am also curious if you can restore some of the gain by reversing the circuit so that the current can flow the other way.

It just might be possible to restore the atomic balance unless you have actually changed the crystal structure.

I wish I had the time to sit down and think this through. Very intriguing.

DAB