Chinese Germanium 1N34

** FFS - READ the rest of my post you snipped to pieces.

You steaming f****it.

Yes, all diodes can "zener" but they are reversed biased.

One surplus store here used to sell "zeners", some specific voltage, and they were plastic encased transistors with a lead cut off. They must have gotten them that way.

Michael

Explain which part and you'll get some deeper answer.

Michael

The USians kept trying to use tubes as mixers, and they didn't work well at GHz. The Brits pushed point-contact diodes, which worked. The trick was then to keep the megawatt transmit magnetrons (another Brit contribution) from blowing out the delicate receive mixer diodes.

By the end of the war, we were building radars that had ranges about

2:1 worse than the theoretical limits.

And that caused the 1N34 to come along after the war,

Good book:

The prime material is the MIT RadLab series, published just after the war, to document the technology. Volume 15 is "Crystal Rectifiers"

Good stuff, the birth of modern electronics.

Interesting reference, Turner. I hadn't heard of him before.

The b-e junction of a transistor often makes a good zener, roughly 5 volts typically.

There are some transistors that you can use emitter to collactor as a reference zener, which is a zener with a forward diode in series, with a net tempco near zero. That's a lot cheaper than buying a classic

2-chip reference zener. 6.2 volts seems to be the magic number.

Of course, IC references are better now.

So what? All standard zener diodes are used in reversed bias mode too. Go back to basics.

I thought someone here or elsewhere mentioned that Zener effect is not necessarily the same as the avalanche effect in regular diodes.

I'm gonna have to try that! just for kicks

The physics is different, zener (quantum tunnelling) at low voltages and avalanche at high voltages, midway being around 5 volts maybe.

Most people and data sheets call all such diodes "zeners."

Somewhat like "Xerox" for all photocopiers.

A word of warning: don't test the reverse bias on point-contact, or light emitting, or low-noise photodiodes. Those devices have very sensitive near-surface regions that only stay clean if the electric field isn't given an unexpected polarity.

The base-emitter junction of a transistor is normally buried (far from the surface) so it is a useful and stable zener for many purposes. There are also diodes made in TO-92 cases, where 'extra' wires would be trimmed as a last step in manufacturing. I recall varactor and current-regulator diodes in such packages.

_Forward_ biasing some photodiodes can lead to tears, due to horrible current crowding at the contact. However, at least with Si, Ge, and InGaAs devices, reverse bias causes no worries right up to the rating.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Reverse biasing photodiodes is the usual way to use them. It reduces their capacitance and makes them a lot faster.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Like I think I said earlier, the microwave diodes out of WWII like the

1N21 do not like to be tested, but I can't remember if that was merely because at the time a VOM would put too much current or voltage into it, or if the diodes are especially finicky. I remember saying something about a 1N21 to someone, and he said "you shouldn't have done that..." and I have seen (but can't remember techniques) for testing such diodes.

LEDs can be reverse biased, but I gather they have relatively low reverse voltage rating, so you merely want to be careful.

Michael

I've seen LEDs in cheap Chinese and Indian products run directly from 230VAC with a single series resistor and nothing else. That obviously places the LED in reverse breakdown every half cycle. I haven't paid enough attention to see if/how their performance changes with time.

Anyone tried taking a garden variety photodiode up to the point where it starts avalanching? (Maybe in a dark room... there are some thing better done with the lights off :^)

George H.

I reversed biased several LEDs.. most were good up to ~100V or so..

230VAC seems like a lot... but maybe with the "right" led.

George H.

I see now how my post could be incorrectly interpreted. I mean a

*single* LED used as a power indicator, not a string of them, and without any other component shunting it to prevent reverse operation. The series resistor limits the current in both forward and reverse breakdown mode. Usually these are run at a mA or two. The preceding post by whit3rd made me wonder if LEDs used like this suffer significant degradation in light ouput or lifespan.

No, but that's what an APD does (probably with special doping)

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com