Tunnel Diodes - Page 1
Forum section: electronics / general

author: bradleytron
author_rank: Regular Contributor
timestamp: March 10, 2013, 12:37:37 am
content: Hello folksI was looking into a circuit application that utilizes negative resistance and thought I could could just find and purchase a few tunnel diodes to do the trick. Turns out that my effort was in vain, very few suppliers, expensive minimum qualtities and long lead times. In fact I could not even find a local electronics supplier like digikey that carries them. Does anyone have experience using FETs or BJTs to get the equivalent effect? Thanks very much for your insights.BT

author: westfw
author_rank: Super Contributor
timestamp: March 10, 2013, 02:08:00 am
content: Also look at "sidactors."

author: bradleytron
author_rank: Regular Contributor
timestamp: March 10, 2013, 03:41:23 am
content: Quote from: westfw on March 10, 2013, 02:08:00 amWill do, thanks again, very much for the help.BT

author: bradleytron
author_rank: Regular Contributor
timestamp: March 10, 2013, 03:48:02 am
content: Quote from: westfw on March 10, 2013, 02:08:00 amHi again, I looked at data sheet for a SIDACtor but could not find any portions of I-V relationship with a negative slope. I'm looking to replicate the 'negative' I-V slope portion of the response typical with tunnel diodes and I understand that some people have managed to achieve this using BJTs or FEts. Could you clarify if neccessary what aspect of the operation of a SIDACto you were thinking of?ThanksBT

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:03:54 am
content: I had to build a tunnel diode oscillator in college lab class, and later encountered them in test equipment I repaired, like Tektronix products.Probably about ten years earlier, I was fascinated by glowing sparky things, and learned about relaxation oscillators and negative resistance. with a 90 volt battery and an ne-2 neon lamp and capacitor.Would blink for a decade, how long did your first hello world arduino led blink?So when doing lab for the diode, it was old hat.Lot's easier to "blink an led" back then. 3 parts.

author: amspire
author_rank: Super Contributor
timestamp: March 10, 2013, 04:11:01 am
content: The early tunnel diodes used to be germanium, but even though there are silicon tunnel diodes (and other materials), I think the big problem is that until there is a modern IC-type process for making them, they are not cost effective. Here is a picture of a silicon tunnel diode:This site was selling old GE germainium tunnel diodes. The site is dated 2008, so you want to contact them first before ordering:http://semiconductormuseum.com/MuseumStore/MuseumStore_1N3712_Index.htm

author: PaulAm
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:29:40 am
content: Russian made devices show up on ebay fairly often. If you're looking for production quantities, you're probably out of luck.

author: c4757p
author_rank: Super Contributor
timestamp: March 10, 2013, 04:30:15 am
content: What about a PUT? 2N6027 is readily available.

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:31:28 am
content: I think I was only one who got it running in the class lab kit. I faintly remember having a hp current and voltage regulated supply handy, and knowing how my neon bulbs worked, got it going.This was a new tech school, so the teacher was unpacking the projects from the dodgey suppliers.I am one in favor of knowing the basic physics and math no matter how annoying, they become fun at times, so learn it anyway, it is rewarding and necessary but agree you will not encounter this in a production engineering environment.

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:34:02 am
content: UJT is not a tunnel diode, I like the memory of ujt's though, worked at Bell labs facility and decades later avionics that used the things. Actually I miss them.

author: c4757p
author_rank: Super Contributor
timestamp: March 10, 2013, 04:36:01 am
content: No, of course a UJT/PUT is not a tunnel diode, but they do exhibit negative resistance.Not to derail the thread, but what did they use them for? For some reason I'm absolutely fascinated by (semi-)obsolete semiconductors, and I picked up a few of the things recently to play around with, but I honestly can't think of a legitimate use for them. I suppose I could use one as method number 467 to make a generic oscillator, but what else were they used for?

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:39:37 am
content: yes c4757p that's what we mean, and thanks, amspire for that grat image, now curious to explore the tunnel diode again (some may be in my basement scope junkpile)

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:48:00 am
content: c4757p, they are good for pulse generators, like an r/c time constant thing.. If you want to breadboard one, I'll try to recover from my geriatric mind some fun stuff. This is all much more fun than opening the new smart phones my wife and I succumbed to today.(But hey it is 20 dollars cheaper per month than if we stayed with our feature phones).You set them up to output a pulse with a resistor and cap. In the meantime look up relaxation oscillator with neon bulb. was grammar school kit for me.

author: c4757p
author_rank: Super Contributor
timestamp: March 10, 2013, 04:54:03 am
content: Oh, yeah, I know that. I was hoping they were used for something more exciting than an oscillator...

author: jh15
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:57:42 am
content: Well, they were high rel enough to be used in our Boeing aircraft instruments of the 70's and 80's, and I never found a failed one in any of the other companies instruments either.

author: amspire
author_rank: Super Contributor
timestamp: March 10, 2013, 05:35:53 am
content: One of the pioneers of tunnel diodes was General Electric. I have a book GE Transistor Manual (1964) and it is really interesting.Back then, they though tunnel diodes were going to be huge in computers because they were always super fast at a time when germanium transistors were pretty slow.There are a number of circuits of logic circuits, flip-flops, decade counters. I have never heard of anyone actually using tunnel diode for logic.Other uses other then the conventional rf oscillators were staircase generators with multiple diodes, thyristor trigger circuits, temperature sensors in the form of a temperature sensitive oscillator, the frequency divider in a crystal controlled clock (synchronous divider stages), radiation and light detector, microwave amplifiers, and fast autozero circuit for an opamp.GE really thought they would become huge at the time.The other device that was sure to become huge was Silicon Controlled Switches - like a SCR but with gates from both of the inner silicon layers rather then just one. They were going to be big in logic circuits, but unfortunately they were just very slow. Probably the instant RTL and TTL ICs started appearing, they were dead.There is a chapter on a brand new device - the silicon planar epitaxial axial diode like the SD100, SD300 and the gold doped SD500. These were a revolution as the preceding diodes used platinum whiskers and springs to make the contact with the anode. These had both the anode and cathode fused to the lead ends and were very fast.Never heard of them?The SD500 is more commonly known as the 1N914.

author: SeanB
author_rank: Super Contributor
timestamp: March 10, 2013, 05:54:21 am
content: UJT's make a very nice oscillator, and do well at that over a wide range. I never dealt with tunnel diodes, but they are nice. You can do logic with them, along with memory, but they never took off. The UJT oscillator in avionics was almost always used as part of light dimming and power supplies to generate the linear ramp for a PWM system. Avionics was probably the first to use switching power supplies in the 1960's to power onboard computer systems. You could get a supply that provided 5V 50A in a package about the size of a butter brick. Actually it was 2 5V 50A supplies, one powered all the time and the identical other half ran at 400Hz, providing a switched 5V rail to supply the logic with power only when needed to calculate. Used air cored 12AWG inductors and a massive heatsink with the stud diodes and TO3 transistors on it, with a switching frequency of around 1MHz. Only a 10uF output capacitor on it, and around 100 10n capacitors distributed over the logic boards.

author: westfw
author_rank: Super Contributor
timestamp: March 10, 2013, 10:29:54 am
content: QuoteWikipedia says it well:http://en.wikipedia.org/wiki/DIACI guess the curve is pretty dramatically different from a tunnel diode, but you can build oscillators out of them. Rather like a neon bulb or a spark gap.

author: Gall
author_rank: Frequent Contributor
timestamp: March 10, 2013, 11:10:50 am
content: I happen to know the replacement for tunnel diode! Strictly speaking, it is lambda-diode, nut there is very little difference.It is made of two similar depletion mode JFETs, one n-channel and one p-channel. Connection is source-source, gate-drain, gate-drain. The drains are teriminals of the "diode". A real tunnel diode has lower working voltage but everything else is similar.I also found some NOS tunnel diodes sellers in ex-USSR countries. They are $0.30-$2.00 each. Look for AI301 or everything else that starts with "AI, "GI", "1I", "3I"."G", "1" = Germanium"A", "3" = Gallium Arsenide"1", "3" = Military grade"A", "G" = Commercial gradexI1xx (like AI101) are for amplifiersxI2xx (like AI201) are for generatorsxI3xx (like AI301, GI306) are for switching circuits or general usexI4xx are Backward Diodes for switching circuit and general useThey are sold on eBay here and there. "RuTubeStore" and "SOVCOM" eBay stores have lots of them.

author: c4757p
author_rank: Super Contributor
timestamp: March 10, 2013, 02:45:25 pm
content: Quote from: Gall on March 10, 2013, 11:10:50 amThat's pretty cool. No P-channel JFETs on hand, but a quick LTspice "curve tracer" verifies this.Edit - seems that you can use a PNP transistor and a couple of bias resistors in place of the P-JFET. Looks like I have a new toy for todayQuoteThat generally seems to be a decent way to get small quantities of obsolete stuff. I got a few Ge transistors that way.

author: TerminalJack505
author_rank: Super Contributor
timestamp: March 10, 2013, 03:45:19 pm
content: Quote from: amspire on March 10, 2013, 05:35:53 amThis posthas a link to the manual in PDF form for those that are interested.

author: PaulAm
author_rank: Frequent Contributor
timestamp: March 10, 2013, 04:01:38 pm
content: Tektronix extensively used TDs in trigger and pulse generator applications in the 60s and 70s..Here's a page on the Tek 422, a dual channel 15MHz scope from the mid to late 60s:http://w140.com/tekwiki/wiki/422Check out the trigger circuit. It's very simple, but extremely robust. On the 422 I have, it reliably triggers past 60MHz where the vertical response essentially goes to zero.Tektronix also used them in sub ns pulse generators.

author: Gall
author_rank: Frequent Contributor
timestamp: March 10, 2013, 07:07:30 pm
content: Quote from: c4757p on March 10, 2013, 02:45:25 pmIf you need to know parameters for that stuff, let me know. I have selection guides and tables of basic parameters for most of these old parts - of course, in Russian.