piglet wrote:> You used to be able to buy four-layer diodes (also sometimes called > Schockley diodes - not to be confused with Schottky!) in a range of > voltages. Became obsolete mid 1970s. I had to service gear that used them.You mean the DIAC? They are not obsolete, just niche. Still used in TRIAC dimmers and self-oscillating half-bridge converters for halogen lamps, etc. The immortal DB3, for instance. Best regards, Piotr
Negative resistance with BJTs
Started by ●August 22, 2018
Reply by ●August 22, 20182018-08-22
Reply by ●August 22, 20182018-08-22
On Wednesday, August 22, 2018 at 4:43:24 AM UTC-7, daku...@gmail.com wrote:> a four layer diode, consisting of alternate p, n layers acts as a > negative resistance, and can be realized in practice with a pair > of NPN and PNP transistors, connected in specific ways. Now, is > it possible to achive this a series connection of two discrete > diodes ? I was just thinking about it.Two discretes, no; there have to be carriers passing through one layer into the next without recombining, and a metal wire always recombines 'em. The two-transistor connection is just an SCR, and the negative resistance comes from its breakdown voltage. The commercial diode device that contains that circuit, a diac, is commonly used for SCR triggers, though I recall it also being used for fox& hound type wire tracing.
Reply by ●August 22, 20182018-08-22
On 2018-08-22, dakupoto@gmail.com <dakupoto@gmail.com> wrote:> a four layer diode, consisting of alternate p, n layers acts as a > negative resistance, and can be realized in practice with a pair > of NPN and PNP transistors, connected in specific ways.Yeah, you get a PUT or SCR depending on which node you nominate as gate.> Now, is > it possible to achive this a series connection of two discrete > diodes ? I was just thinking about it.sure, but you'd need to decapsulate them grind the dies and somehow fuse the silicon together just right... -- ت
Reply by ●August 22, 20182018-08-22
On 08/22/2018 08:48 AM, tabbypurr@gmail.com wrote:> On Wednesday, 22 August 2018 12:43:24 UTC+1, daku...@gmail.com wrote: > >> a four layer diode, consisting of alternate p, n layers acts as a >> negative resistance, and can be realized in practice with a pair >> of NPN and PNP transistors, connected in specific ways. Now, is >> it possible to achive this a series connection of two discrete >> diodes ? I was just thinking about it. > > Maybe if you sawed them open at exactly the right point & fused the silicon dies together... otherwise they're just 2 diodes, with the middle p&n layers not in contact with each other. > > > NT >The first transistors were made by adding a cat's whisker base connection to a diode. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●August 22, 20182018-08-22
pcdhobbs@gmail.com wrote:>>> You can also do it with a single transistor at AC. > >> Out of curiosity: do what? > > Make a negative resistor. Start with an emitter follower and put a > small capacitance on the emitter. The input resistance goes negative. > That's why you have to use beads, anti-snivet resistors, and so on.Snivet?
Reply by ●August 22, 20182018-08-22
On Wed, 22 Aug 2018 21:14:35 +0200, Piotr Wyderski <peter.pan@neverland.mil> wrote:>John Larkin wrote: > >> RF diodes, gunn and such, oscillate. > >Gunn is not even a diode, or -- if you prefer -- a junctionless one. :-] >Amazing construction, BTW. > > > As a kid, I tried using two diodes as a transistor. Apparently lots of > > people did that. > >+1 > >When you grow up, you start using transistors as diodes... > > Best regards, PiotrFunny. Some NPN transistors can be used as "reference zeners" to make 6.2 volts at a very low TC. That's the zenering b-e junction in series with the forward-conducting b-c. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●August 22, 20182018-08-22
whit3rd wrote:> On Wednesday, August 22, 2018 at 4:43:24 AM UTC-7, daku...@gmail.com > wrote: >> a four layer diode, consisting of alternate p, n layers acts as a >> negative resistance, and can be realized in practice with a pair >> of NPN and PNP transistors, connected in specific ways. Now, is >> it possible to achive this a series connection of two discrete >> diodes ? I was just thinking about it. > > Two discretes, no; there have to be carriers passing through one layer > into the next without recombining,Why? An electron enters the wire and another comes out the other end.> and a metal wire always recombines > 'em. The two-transistor connection is just an SCR, and the negative > resistance comes from its breakdown voltage. The commercial diode > device that contains that circuit, a diac, is commonly used for SCR > triggers, though > I recall it also being used for fox& hound type wire tracing.The Fox and hound I looked into just had the antenna going into an LM386.
Reply by ●August 22, 20182018-08-22
On Wed, 22 Aug 2018 19:34:04 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 08/22/2018 08:48 AM, tabbypurr@gmail.com wrote: >> On Wednesday, 22 August 2018 12:43:24 UTC+1, daku...@gmail.com wrote: >> >>> a four layer diode, consisting of alternate p, n layers acts as a >>> negative resistance, and can be realized in practice with a pair >>> of NPN and PNP transistors, connected in specific ways. Now, is >>> it possible to achive this a series connection of two discrete >>> diodes ? I was just thinking about it. >> >> Maybe if you sawed them open at exactly the right point & fused the silicon dies together... otherwise they're just 2 diodes, with the middle p&n layers not in contact with each other. >> >> >> NT >> > >The first transistors were made by adding a cat's whisker base >connection to a diode. > >Cheers > >Phil HobbsThe "base" got its name because it was the semiconductor slab. The emitter and collector were the point contacts. https://en.wikipedia.org/wiki/Point-contact_transistor When I was a kid, I got a tour of Bell Labs and had lunch with Walter Brattain. Nice old guy. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●August 22, 20182018-08-22
"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in message news:plkt8p$vtq$1@dont-email.me...> pcdhobbs@gmail.com wrote: >>>> You can also do it with a single transistor at AC. >> >>> Out of curiosity: do what? >> >> Make a negative resistor. Start with an emitter follower and put a >> small capacitance on the emitter. The input resistance goes negative. >> That's why you have to use beads, anti-snivet resistors, and so on. > > Snivet? >Hah, Phil's showing his age\\\experience? :-) "Snivets" was an oscillation that sometimes affected vacuum tube television sets, where the horizontal sweep driver had UHF oscillations for part of its operating cycle, apparently due to the cavity formed between screen and plate, and the exact electron beam density and electrode voltages applied. (I know this from books, certainly not from seeing the phenomenon in person. I don't know that it was something that happened randomly in any set; I suspect it was more of an early problem, and/or a Muntzing problem. Back in the era when, y'know, Muntz was a real brand and everything. :-) ) Tetrodes are well known for having a negative resistance region on the plate curve (due to secondary emission diverting plate current to the screen), and beam tetrodes less so but still to some extent in some parts of their operating range. But I don't know that it's a fast enough phenomenon to cause UHF oscillation. The usual description implies it's a problem with the internal design of the tube itself, which doesn't suggest it would be a universal problem, only an early one. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
Reply by ●August 22, 20182018-08-22
>"Snivet? "One of the uses for the term was the microwave emissions emitted by tetrodes, pentodes and beam power tubes when used as switchers, such as a horizontal output (or LOPT) in TV sets. It was pretty much eliminated by putting a positive voltage on the suppressor grid, which of course would not work with tetrodes. It only became a problem with the introduction of the UHF TV band. The snivets were not detected by common test equipment but interfered with the UHF band. They used to cause mostly vertically oriented black oval "holes" in the picture, almost always to the right. They were modulated by line frequency which indicates that the filament voltage was involved because everything else was filtered. As far as I know, this phenomenon did not occur with semiconductor devices. But then...we have this.
