Ya better hurry, only two left and he (says) he sold 78. He goes on to say you can get a shipping quote if you want to buy massive quantities. Quantity 1 - $152.58 USD, That's greedy, he should offer free shipping. :-) Mikek
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Looks like you have some gross amount of series resistance and parallel conductance. Not too surprising in a 1N34A!
Cheers
Phil
-- 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
Nobody said they were ideal.
They are "the best" in some circumstances, which probably at this point means when low forward voltage drop is desired.
Michael
The best RF detector diodes are germanium back diodes, which are actually tunnel diodes with very low peak point currents. They are used "backwards" from the obvious polarity.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
During WWII, we (US and Brits) were using silicon, germanium, and gallium arsenide point-contact diodes as mixers up to 30 GHz. One of the RadLab books notes that "a semiconductor triode should be possible."
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The point contact is just weird. Here's a plot of the same data but log-log.
My eye wanted to put put two lines through the data, so lines were added by eye. Two power laws?
George H.
So first, here is what mine look like:
except that they don't seem to have any visible marking
Second, I wanted to create a diode curve tracer to test these new diodes using scope X-Y mode. Problem of course that my ramp generator is grounded so I can't probe at two different point pairs.
It's funny how I had all these complicated ideas to solve this problem including using a difference amplifier to convert the voltage difference across the diode to a voltage referenced to ground.
Then I decided to google search, and after 5 mins, it's funny how the solution was way simpler. Plug the function generator into a 3-2 prong adapter. DUH!
That's normal. The so-called 'ideal diode equation' is Shockley's model for a planar diode (i.e. the depletion region is constant area, variable thickness), but a point=contact diode has a depletion region which is a hemisphere around the point of contact (area proportional to R squared).
The Ge point contact diodes worked well, because the low bandgap made impurities relatively benign (and that contact point has to be at the semiconductor surface, which is always dirty). Capacitance was low, and gigahertz operation was easy. Silicon point contact isn't as reliable because there's more dirt sensitivity, and the higher forward voltage means a surface electric field (attracts more dirt).
Shottky diodes for RF are not point-contact types. Are ANY point-contact diodes still in production?
Finally, with my scope diode curve tracer, I got some data.
1- A schottky diode (1N5189) -> turns on around .2V and then current goes u p really fast 2- A Germanium diode with clear glass and a green stripe -> turns on around .2V but current rises REALLY slowly with voltage. I knew this already. Ger manium diodes have less steep curve and that's why they have some applicati on in audio.3- My presumed 1N34 -> turns on around .2V but current rise slower than (1) and faster than (2).
So at this point I wasn't sure, so I dug around for more "clear glass" germ aniums I had. I found one that looks almost identical to diode #2 but with a black stripe rather than a green one. I put it in my test circuit, and th e result is almost identical to #3.
So I can't tell if my diode is 1N34 or not, but I'm positive it could be a Germanium diode since it acts like another Germanium diode.
Time to give the seller positive feedback!
** Well, they are cleary zener diodes - like the link says.
The chip is trapped between two headers to carry heat away.
Small silicon diodes like the 1N4148 look similar.
It sure ain't no point contact type.
.... Phil
Ahh OK so as I forward bias it the area of the depletion region changes. (Does it get smaller with forward bias..? Just thinking out loud, I'd guess it gets larger in area with a reverse bias.)
Looking at my rather sketchy data, the slope at low bias is ~1 (in a power law) and ~2.5 or so at higher bias voltages... with the crossover point near 30 mV or so... Near the thermal voltage. (I have no idea if that is significant or not.)
I could only find I-V of reversed biased Ge on a quick web search.
George H.
Have you ever seen low forward voltage zener diodes? That would be new to me. The forward drop on these are about .2V-.3V
** But the pic IS of some Philips zeners - it damn we says so.
Piss off fool.
.... Phil
A zener by definition is reverse biased.
Using diodes as voltage regulators is not uncommon. Just put a bunch in series to get the desired voltage from the individual voltage drops, and then feed that with a resistor. But it's not a "zener effect".
Germanium diodes can be used the same way, but their forward voltage drop is lower, so unless the desired voltage is low, you'd need more. And the termperature response is different from silicon, and that may be a factor.
It's not uncommon to use a forward biased silicon diode as the sensor in a digital thermometer, the characterstic is well known. I can't remember if germanium diodes were used that way, but if so, the response would be different.
But this factors in when forward biasing diodes for better low level response, such as detecting low RF voltages. Once you bias the diode, the will react to temperature, so you need another diode similarly biased but with no RF applied to it, to balance out the temperature response.
Michael
** But in practice may be either.
Back to back zeners are very commonly used for anti-static protection plus for AC voltage limiting and clamping in all kinds of analogue circuitry.
... Phil
Huh ?
sure I have, after they get hammered a few times! :)
Jamie
What happens if you forward bias one? Thought ceases to exist? Or does it just disappear in a flash of logic?
I'll have to try it. ;)
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
That's why I said "Looks like" not "exactly absolutely identical"
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