Unusual functions of cheap parts

Hi Jim -

And on what delay timescale it works?

regards - Henry

"RST Engineering" schrieb im Newsbeitrag news: snipped-for-privacy@corp.supernews.com...

BA682.

A step-recovery ("snap") diode works on the principle of stored charge in the diode. During the forward biased half of the AC waveform, the diode is a very low impedance and it stores excess charge; during the reverse biased half of the waveform, the diode remains a low impedance until the stored charge is depleted, at which time the diode "snaps" into high impedance. This snap acts much like a spark-gap transmitter, in that a tremendous number of higher order harmonics are generated. In general (and there are ways to enhance this), the power available from any harmonic is around 1/n * Pin, where n is the order of the harmonic and Pin is the RF power input to the diode.

Biasing the diode simply varies the point on the reverse cycle of the AC waveform where the diode snaps. For maximum power, you try to get the diode to snap at the peak of the waveform. However, by varying the diode bias, you can get it to snap before or after the peak of the waveform. Generally you can get it to snap plus or minus about 30 degrees about the peak before the snap action degrades.

60 degrees of phase shift is nothing to talk about unless you are working with the 10th harmonic, which means a phase shift of 600 degrees. Now you've got something to work with.

Jim

Well, then the cook is to blame, not Labskaus per se. Go to Hamburg and visit the "Old Commercial Room". I guess they make still delicious Labskaus.

Oliver

--
Oliver Betz, Muenchen (oliverbetz.de)

Looks a lot like ordinary corned beef hash to me, if a little less coarsely chopped.

But I wonder why they serve it with one of these?

;-) Rich

You could also serve with one of these:

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

the problem is, that it is an rf-transistor and can't be driven at

30V/0.2A, I found a complementary in an old table KTT, the 2N2894A, but it also has max. 12V, so I find no other than the 2N3906.

If I simulate with the 2N3906, the frequency response is not worse than with the 2N2894A.

mfg. Winfried

From a cursory search, it looks like it'd be kinda hard to find one these days. ;-)

Cheers! Rich

He looks like this these days:

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

National Semi's (now Fairchild) 2n5771 was a gold-doped PNP. ft>=850MHz. For avalanche mode one might try the lower-Vce-rated PN3640 (12v), or PN3639 (6v).

I might even have notes on this. I tested/compared various BJTs in avalanche mode some years ago, trying to find the "best." ISTR picking the 2n2369, both because it was fast, and because it avalanched reliably where other types wouldn't.

James Arthur

Hi, James,

Interestingly, the best avalanchers aren't usually super-fast transistors, but old klunky things. The Zetex avalanche transistors have lowish Ft's and are made in Russia, maybe on an old process.

John

Howdy John, I was unclear: by "...it was fast..." I meant the 2n2369 was one of the devices with the fastest avalanche edges.

Digging through some of my notes, I don't see the BJT comparison, but a 2n2222 biased to +100Vce, banged / triggered by a 74HC-series gate, gave synchronous 750pS risetime pulses. Not very impressive, really, though good for higher-power stuff than I needed.

Interestingly, I found a 74AC00 driving an MPS2369 was faster & less trouble: 360pS fall (turn on) time, & 570pS rise (turn off) time, and no nasty high voltage supplies. It was possibly even a little faster than measured--at 360pS I was pushing my poor little 7S14 1-GHz sampling plug-in pretty hard.

Best, James

Is there a known figure of merit that would help select devices types for fast avalanche breakdown?

--
newell

That was a high-frequency part for the time, spec'd at 1200MHz...

An old Raytheon datasheet says the 2N2894 was doped with platinum.

BTW -- in AoE, we list the 2n5771 as a PNP complement to the NPN 2n5769, both 15V plastic versions of older metal-can parts.

--
 Thanks,
    - Win

I was thinking of the "bismark roll", which I had thought was some kind of jelly donut, or "bismark donut", which would be like a jelly roll.

But I can't find a single reference to the thing except at the wikipedia disambiguator page, and all it has is the blurb, something like what I said.

Oh, well. :-)

Thanks! Rich

Thank you Jim for your longly explanations. I already knew the charge storage process, but the phasing aspect was new and interesting. My question about phase delay was in another direction. To be concrete: How to delay (=phase shift) a 145MegHz signal (mostly sinus waveform) with a snap diode? After reading your explanation I cannot see how to achieve a non-snapping action here. Maybe that would work with the diode if you modulate it with dc current getting delay in the ps timescale. Another question would be if it possible with the snap diode to make a power amp in some form of ringing oscillator. Of course, it should be modulable at least with FM.

- Henry

"RST Engineering" schrieb im Newsbeitrag news: snipped-for-privacy@corp.supernews.com...

is

biased

*

diode

Generally

before

[snip]

Thanks for tracking that down, Win! Gold in a PNP was certainly troubling my ancient remembrance of semiconductor chemistry.

...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  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Very interesting. The 1N4007 seem to be very versatile devices. They are available with a SOD-57 glass envelope, too (1N4007G?). These are fairly well photoconductive. When illuminated by a high efficiency IR LED (HSDL-4230 or so) current transfer ratios of 0.001 can be achieved. Not too much, but with two LEDs 100uA of photocurrent is obtainable. This is OK for a pass element in an "electrostatic" power supply for e.g. electron or ion lens systems.

--
mfg Rolf Bombach

A high-voltage optocoupler; cool.

I've posted a schematic for a hv opamp (400 v p-p) that uses two optoisolators as the output push-pull stage... it's very cheap and simple. A higher-voltage photodetector, like a glass power diode, sounds useful, too.

I worked once with a company in Southern California that had a neat gadget: it was a truncated cone of silicon with gold contacts on the base and the flattened apex. It would stand off something like 5KV until you whacked it from above with a laser, illuminating all the sides of the cone, whence it would conduct hard. I think they went out of business, though; it was pretty obscure.

John

While many companies* are making 1n4007G glass-passivated diodes, it appears they all cover the glass with plastic. I wonder... where one can get a 1n4007 with an all-glass package these days?

• Including unusual semiconductor manufacturers, like: Won-Top, Bytesonic, Leshan Radio, Formosa Microsemi, Gulf Semiconductor, Dachang Electronic, Goodwork Semiconductor, etc.

--
 Thanks,
    - Win