On Thursday, August 23, 2018 at 10:15:44 AM UTC+10, John Larkin wrote:> 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, Piotr > > Funny. > > 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.This has been well-known for quite some time. The British Journal of Scientific Instruments (now Measurement and Science and Technology) published a short note on the technique in the mid-1960's. I can't find the journal reference, but IIRR the author used a gold-doped switching transistor - perhaps the 2N3904. The residual temperature coefficient (TC) did depend on the current, which had to be somewhere around a couple of milliamps, though the exact current for minimum TC varied from device to device. The author talked about sticking a soldering iron on the package to see which way the reference voltage moved when you heated the part up, and recommended trying a range of currents to bracket the point where the excursion went from positive to negative. -- Bill Sloman, Sydney
Negative resistance with BJTs
Started by ●August 22, 2018
Reply by ●August 23, 20182018-08-23
Reply by ●August 23, 20182018-08-23
>"But I don't know that it's a fast enough phenomenon tocause UHF oscillation." It isn't and it doesn't have to be. think of standing waves in a transmission line. Now think of the plate as a transmission line. It seemed like the frequency was controlled chiefly by the filament voltage, you could see the phase change on the screen as you tuned through vacant channels. So now they needed an extra pin for the suppressor grid. Just connecting it to the cathode did not work. I am not sure how it worked, maybe it was causing the suppressor grid to pick up some localized secondary emission or some shit. Back then it wasn't a issue enough to investigate, so it certainly isn't now. the separation ad positive bias on G3 did the trick and that's all we cared. Before that we tried a million things, one that sometimes worked was to find just the right tube that didn't do that, or at least didn't do it at frequencies used by local stations.
Reply by ●August 23, 20182018-08-23
On 22/08/2018 21:15, Piotr Wyderski wrote:> 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 >Diac and Schockley are close cousins. The 4-layer schockley diode was unidirectional and made in grades from about 7 to 30V often with low TC and close tolerances. The Diac is bidirectional and I think a 3 layer device. Sometimes Diacs are drawn looking like an NPN BJT with two emitters (as in outwards pointing arrow on the "collector"). piglet
Reply by ●August 23, 20182018-08-23
On 23/08/2018 07:00, piglet wrote:> On 22/08/2018 21:15, Piotr Wyderski wrote: >> 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 >> > Diac and Schockley are close cousins. The 4-layer schockley diode was > unidirectional and made in grades from about 7 to 30V often with low TC > and close tolerances. The Diac is bidirectional and I think a 3 layer > device. Sometimes Diacs are drawn looking like an NPN BJT with two > emitters (as in outwards pointing arrow on the "collector"). > > piglet >Wiki has 'em both: <https://en.wikipedia.org/wiki/Shockley_diode> <https://en.wikipedia.org/wiki/DIAC> piglet
Reply by ●August 23, 20182018-08-23
On Wednesday, August 22, 2018 at 5:20:07 PM UTC-7, Tom Del Rosso wrote:> 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.That 'electron' can be an electron in the conduction band going into the wire, or a hole in the valence band coming from the wire. But at the other end of the wire, it's always gonna be the majority carrier for whatever doping is present at the metal/semiconductor junction. Metal/semiconductor interfaces are just as nonlinear as other junctions, and it is very important, for Si integrated circuits, that aluminum can alloy with either P or N material and make an ohmic connection and do it at a low-ish process temperature. IC manufacture depends on that fact just as much as on SiO2 for passivation and insulation.> > 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.Oh, there's a patent that I recall... yep, takes some tracking, but here it is <https://patents.google.com/patent/US4906938A/en> The idea is to make a current modulation, and use the magnetic field around the (unshielded) wiring to sense wires through walls
Reply by ●August 23, 20182018-08-23
On 08/22/2018 07:57 PM, Tom Del Rosso wrote:> 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?Oscillation in a power transistor, especially a power MOSFET. (Pease, P. 88.) 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 23, 20182018-08-23
On 08/22/2018 10:00 PM, Tim Williams wrote:> "Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in > message news:plkt8p$vtq$1@dont-email.me... >> pcdhobbs@gmail.com wrote: >>>>> You can also do it with a single transistor at AC. >>> >>>> Out of curiosity: do what? >>> >>> Make a negative resistor. Start with an emitter follower and put a >>> small capacitance on the emitter. The input resistance goes negative. >>> That's why you have to use beads, anti-snivet resistors, and so on. >> >> Snivet? >> > > Hah, Phil's showing his age\\\experience? :-)Well, only partly. (I'm 1959 vintage.) Mostly it's because I taught myself circuit design out of old ARRL Handbooks and National Semi app notes, among other things. As a kid I used to build tube circuits that mostly didn't work because I didn't know enough. I got most of the parts by taking apart old 1950s and early '60s TVs that I cadged from repair shops because new parts were way beyond my budget. The last tube circuit was about 1990, where I used an 811A to run an electrostatic grid in an ion drift detector. Its combination of high voltage and low capacitance was beyond that of any semiconductor. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●August 23, 20182018-08-23
On Wed, 22 Aug 2018 21:00:38 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>"Tom Del Rosso" <fizzbintuesday@that-google-mail-domain.com> wrote in >message news:plkt8p$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.My uncle Sheldon, the TV repair rascal that taught me electronics, called the vertical bars, from HOT oscillations, "squegging."> >(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. >The circuit that used the negative resistance/noninverting gain behavior of pentodes was called the "phantastron". It was widely used in radar and scopes and timing circuits. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 23, 20182018-08-23
On Thu, 23 Aug 2018 09:29:35 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Wed, 22 Aug 2018 21:00:38 -0500, "Tim Williams" ><tiwill@seventransistorlabs.com> wrote: > >>"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. > >My uncle Sheldon, the TV repair rascal that taught me electronics, >called the vertical bars, from HOT oscillations, "squegging." > >I remember squegging. Didn't remember snivet though. Very useful word ! Just found this site.... http://www.eenewsanalog.com/news/electronic-slang-old-and-young-0/page/0/4# snivet A short burst of spurious oscillatory circuit behavior. �A snivet appears on the output waveform when it crosses zero.� spudger An adjustment tool of variable capacitors or inductors that is nonmetallic and nonconducting so that it will not influence the adjusted value. Spudgers are usually made of plastic and thus have a permeability close to that of air. squegging Spurious frequency modulation in an oscillator caused by noise or instability. �The high-voltage supply is squegging in this �scope, causing the intensity and focus to vary.�> >> >>(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. >> > >The circuit that used the negative resistance/noninverting gain >behavior of pentodes was called the "phantastron". It was widely used >in radar and scopes and timing circuits.
Reply by ●August 24, 20182018-08-24
Phil Hobbs wrote:> On 08/22/2018 07:57 PM, Tom Del Rosso wrote: >> 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? > > Oscillation in a power transistor, especially a power MOSFET. (Pease, > P. 88.)Well that's very different from the other answers. You mean this is a characteristic of the transistor by itself, under certain conditions, regardless of the circuit? Which Pease book? I know of one but I thought there was another.
