On Wed, 13 Sep 2017 20:43:52 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 09/13/2017 07:52 PM, John Larkin wrote: >> On Wed, 13 Sep 2017 16:29:34 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 09/12/2017 01:58 PM, John Larkin wrote: >>>> On Tue, 12 Sep 2017 12:10:40 -0500, "Tim Williams" >>>> <tmoranwms@gmail.com> wrote: >>>> >>>>> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message >>>>> news:QfydnRoVYIpmXirEnZ2dnUU7-YfNnZ2d@supernews.com... >>>>>> That's plausible, since the TC of avalanche current is small and negative, >>>>>> so hot spots would avalanche slightly less. However, depending on the >>>>>> construction of the diode, there may be some fairly significant lateral >>>>>> resistance in the epi. >>>>> >>>>> That, and sensitivity to defects. Wasn't that the problem with the early >>>>> diodes (before 1N4007 and the like arrived), they worked majestically well >>>>> within ratings, but could be toasted at the drop of a hat from a little >>>>> overvoltage? >>>>> >>>>> The implication being, I guess, faults in the junction, or even more likely, >>>>> along its edge, causing uneven avalanche (or weirder things) and rapid >>>>> failure under adverse conditions. >>>>> >>>>> Speaking of, when were guard rings developed? That, and careful control of >>>>> surface states (purity, cleaning, and passivation), must've been critical >>>>> steps towards reliable parts. >>>> >>>> Early silicon diodes, and some still I think, were just diced from a >>>> big diffused wafer. Envision lots of edge damage. >>>> >>>> >>>> >>>>> >>>>> >>>>>> Something like a MELF package would reduce this, because the metal makes >>>>>> contact over the whole surface of the die. Maybe the metal contact covers >>>>>> the whole die in the SMT parts as well, I don't know. >>>>> >>>>> Hmm, interesting thought. Also good way to get heat out -- one terminal is >>>>> even in contact with the junction side (for epitaxy or one side diffusion). >>>>> The lead can share in the first tens of microseconds of heating. >>>>> >>>>> For pulses on the order of what JL's talking, it's all about die size, and a >>>>> little about what's immediately touching it. >>>>> >>>>> >>>>>> I haven't measured it myself, but I doubt that zener recovery is slow at >>>>>> all. In reverse bias there's no stored charge in the junction, and so >>>>>> nothing to shield out the applied field. >>>>> >>>>> Zener breakdown, per se, is a tunneling phenomenon, which I would think is >>>>> pretty darned fast, both on and off. Avalanche should have a tail, but it >>>>> might be so fast (i.e., charges sweep out "instantly" because of the high >>>>> field and fully depleted junction) that you can't tell. >>>>> >>>>> BJTs under avalanche can take tens of microseconds to recover, but part of >>>>> that is due to the three-layer design*. I'm not sure how much is comparable >>>>> between BJTs and diodes. >>>>> >>>>> (*Hmm, it would entirely come down to the shielding effect of the base >>>>> layer, no? And likewise, one should expect quicker recovery when smaller >>>>> R_BE, or a B-E discharge circuit, is used. I should test that.) >>>>> >>>>> Regular power diodes are susceptible to dynamic breakdown (applying a high >>>>> reverse voltage during / just after reverse recovery), and I would expect >>>>> zeners to be as well. At least there are very few situations, where you'd >>>>> need to worry about a zener diode's behavior as it goes suddenly from >>>>> forward to reverse bias. And with the higher doping (of most "zeners", >>>>> including true zeners, obviously), it would be that much harder to trigger. >>>> >>>> There is a second Grehkov effect: apply a high voltage across a diode, >>>> so fast that it forgets to conduct. When it finally wakes up, it >>>> breaks down in picoseconds. >>>> >>>>> >>>>> Oh hm, speaking of doping, do they do zener diode families by doping >>>>> density, diffusion time, or both to cover the range? >>>>> >>>>> Oh and and, power diodes are often PIN diodes, which gives a lot of room for >>>>> charge drift shenannigans. >>>> >>>> Right, that's the first Grekhov effect, the drift step-recovery diode, >>>> which typically uses PIN-structure high-voltage rectifier diodes. >>>> Combine that with the second one, the sneaky over-voltage thing, and >>>> you can get kilovolt edges at giant currents in picoseconds. >>> >>> And the FCC will have no trouble finding you. ;) >>> >>> Cheers >>> >>> Phil Hobbs >>>> >>>> >> >> https://www.dropbox.com/s/bwaulog6mzx8zkn/T222_Copper.jpg?raw=1 >> >> https://www.dropbox.com/s/q82toc257fv43z8/DSRD_neg-2KV.JPG?raw=1 >> >> Water cooled, -2 kV pulse, 1.4 ns wide, 100 KHz. That's the DSRD >> version without the breakdown booster. That was for a tomographic atom >> probe project. > >One of these days I'd like to see that running, if you still have it. > >Cheers > >Phil HobbsI don't think I do. Haven't seen it in years... might be in storage somewhere. I wound up using the C-B junction of a 1500V TV horizontal-output transistor as the DSRD. The doping profile was accidentally right. That transistor is long gone. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Zener SOAR
Started by ●September 11, 2017
Reply by ●September 14, 20172017-09-14
Reply by ●November 17, 20172017-11-17
