> John Larkin wrote...
>>
>> I asked about the RadLab books in a technical bookstore near the MIT
>> campus. They'd never heard of them.
>
> Yes, out of print. I bought the complete set from
> a guy at Flea at MIT, and gave them to the Institute.
> One book specializes in high-power radar pulses.
Reply by Michael A. Terrell●February 27, 20172017-02-27
John Larkin wrote:
> On 21 Feb 2017 11:47:50 -0800, Winfield Hill
> <hill@rowland.harvard.edu> wrote:
>
>> Tim Williams wrote...
>>>
>>> Circuit, for posterity:
>>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
>>
>> You should have two sets of drivers and gate
>> transformers, one each for high and low sides.
>> Then you can create an adjustable deadtime.
>>
>> Another attractive idea: pos/neg pulsing to
>> turn a set of MOSFETs on or off, with the gate
>> capacitance storing the state. Combine fast
>> on/off times with low switching frequencies.
>
> The old RadLab radar pulsers were cool. They used the stored energy in
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
>
> I asked about the RadLab books in a technical bookstore near the MIT
> campus. They'd never heard of them.
http://www.nj7p.org/Manuals/Radio_books.php Has all of the books in PDF
format. Download them for free!
--
Never piss off an Engineer!
They don't get mad.
They don't get even.
They go for over unity! ;-)
Reply by Tim Williams●February 27, 20172017-02-27
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:md5qac1s0ekk8j5visjol7qndiolh9slv1@4ax.com...
> They seem to have good lifetimes. You can't fire an avalanche stack at
> a very high rate!
>
> There is a Zetex appnote about using them in series and parallel. The
> cool thing about a series stack is that a small pulse, TTL class, can
> trigger the bottom one, and the whole stack zippers.
Incidentally, I picked up some of the cheaper (not quite) alternative,
FZT857. Rated for 350V, but this one actually snaps beyond 550V!
Seems to avalanche consistently, though appears to have 11.3 ohms ESR when
"on".
Output waveform is interesting, and I don't think it's due to circuit
parasitics (I've got a big fat 1.5nF silver mica on there, so it's not
without stray L).
Circuit is: +HV -- 100k charging resistor -- 1.5nF to GND -- FZT857 (C to
E) -- 50 ohm BNC (terminated). There's 2.2k B-E to make it click.
Rise time is 6ns, up to a plateau at 420V for 14ns. (Vce starts at 580V
before breakdown, so the transistor is dropping a lot of voltage and current
during this time.) Time constant is 92ns, suggesting 61.3 ohm loop
resistance, 50 of which is the termination, so the transistor appears to
account for about 11 ohms.
Recovery (recombination) time about 30us. Varies with size of the pulse
(i.e., size of capacitor).
...
Oh, scratch that... it seems I broke it. It's still avalanching, but now
it's doing it at 440V. I wonder if the plateau is not so much a "buildup"
phase, but a "she can't take anymore o' dis, captain" phase, that causes
damage. (Can semiconductors run out charges to free, so the current
saturates?)
I'm sure a large part of the cost, of the FMMT417s, is just aging. Remember
back in the days when the manufacturers had huge racks of toobs glowing
away? Yeah, like that...
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Reply by Tim Williams●February 23, 20172017-02-23
"whit3rd" <whit3rd@gmail.com> wrote in message
news:14e29d28-92c6-47af-9a9b-274ff5213ea4@googlegroups.com...
> High enough di/dt will also blow up wires.
> I've seen metal-case transistors lose internal wiring that way.
I've seen nuclear bombs lose internal wiring that way. :^)
(Exploding bridgewire, and slapper: supposedly these are used to ignite the
charge. The limited availability of JL's krytron seems to corroborate this
well enough, as do other available documents.)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Reply by Tim Williams●February 23, 20172017-02-23
"Winfield Hill" <hill@rowland.harvard.edu> wrote in message
news:o8k2en0usi@drn.newsguy.com...
> Remember my advice:
> "You should have two sets of drivers and gate
> transformers, one each for high and low sides.
> Then you can create an adjustable deadtime."
>
> Switching one side on at the same time the other
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
Like I said, the dead time is huge -- it's driven with a short pulse, then
zero, then an opposite pulse, then zero. There's no opportunity for
shoot-through. It also helps that the off-side gets reverse bias at the
same time, increasing the noise margin even further!
Still, because of dV/dt, and because of common mode coupling in the
transformer, it might be the problem. Dunno. (But if that's the case, then
splitting the transformer would actually make it worse, because of the lack
of reverse bias. Hmm.)
Measuring the actual gate waveforms, accurately, is unlikely to succeed, so
it's hard to do more than speculate...
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Reply by Tim Williams●February 23, 20172017-02-23
"Winfield Hill" <hill@rowland.harvard.edu> wrote in message
news:o8k1ub0u4f@drn.newsguy.com...
> No, I use the latest rev of Altium Designer.
> However my PCB engineer, Chuck Fisk, who
> retired a few years ago, stayed with Protel.
> Re: colors, I'm constantly honing my choice.
> I dislike Altium's default ground symbol,
> but haven't figured out how to change it.
"John Larkin" <jjlarkinxyxy@highlandtechnology.com> wrote in message
news:desracla2tdbn14t5pi1pdf8cquqlefmfq@4ax.com...
> Avalanching old 2nXXXX parts, like in the old Tek samplers, gave
> pulses that were some fraction of the supply voltage, half maybe. The
> Zetex things really turn on basically saturate, when they fire.
My experience with 2N3904 is it's about 10 ohms "on", which squares more or
less with typical data on RC and RE. Given that those parameters will be a
bit lower due to the huge charge injection.
Recovery time is about 5-10us.
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
Reply by whit3rd●February 22, 20172017-02-22
On Wednesday, February 22, 2017 at 5:07:52 AM UTC-8, Winfield Hill wrote:
> Tim Williams wrote...
> >
> >Aaaand...it's dead. Oh well, fun while it lasted. :^)
> Switching one side on at the same time the other
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
High enough di/dt will also blow up wires.
I've seen metal-case transistors lose internal wiring that way.
Reply by ●February 22, 20172017-02-22
On Wednesday, February 22, 2017 at 1:24:02 AM UTC-5, Clifford Heath wrote:
> On 22/02/17 16:05, Tim Williams wrote:
> > "John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
> > news:md5qac1s0ekk8j5visjol7qndiolh9slv1@4ax.com...
> >> They seem to have good lifetimes. You can't fire an avalanche stack at
> >> a very high rate!
> >
> > You maybe. I've blasted a 2N3904 at 100kHz. :)
>
> Find that appnote Tim. They'll avalanche 60A/20ns for >10E11 cycles.
> See e.g.
> <http://datasheet.octopart.com/FMMT415TD-Zetex-datasheet-8374939.pdf>
>
> Clifford Heath.
On Wed, 22 Feb 2017 03:09:55 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:
>"Clifford Heath" <no.spam@please.net> wrote in message
>news:58ad2e7b$0$32564$b1db1813$19ace300@news.astraweb.com...
>> Find that appnote Tim. They'll avalanche 60A/20ns for >10E11 cycles.
>> See e.g.
>> <http://datasheet.octopart.com/FMMT415TD-Zetex-datasheet-8374939.pdf>
>>
>
>2N3904 likely isn't as robust, but also, notice how much it drops with pulse
>width -- returning to the 61000-4-4 example, the nominal pulse width is
>50ns, but that's only to the 50% level of an exponential decay. Diodes Inc.
>defines pulse width as half-cycle sinusoid,
>https://www.diodes.com/diodes-part-files/DJ/FMMT417/Application%20Notes/201342.pdf
>so the equivalent duration would probably be even longer (100ns?).
>
>That simple hyperbola seems to suggest a deeper truth: that the conductive
>channel has constant voltage drop, and the delivered energy needs to be
>limited to a constant.
>
>Let's see. If the curve is an exponential decay, with a half-life of 50ns,
>then the time constant is 72ns, and the total area under the curve, divided
>by the amplitude, is simply the time constant. So it's more than 50ns, but
>less than 100 at least, not quite as bad as I had been thinking.
>
>There is quite a large disparity between the "no failure" and modest-life
>curves. For this curve, it's about 16A vs. 60A.
>
>Which would be switching impedances of 19 ohms, and 5 ohms respectively,
>which is pretty damn low! And, a stack of ten gets you 3kV into 50 ohms --
>supplying up to 10 hours of continuous EFT duty!
>
>Not as bad as I remember calculating before.
>
>Still, if you need long life, the point about parallel strings stands --
>that's a ~4x reduction in load current, so you need a four strings of ten to
>switch it.
>
>Tim
Avalanching old 2nXXXX parts, like in the old Tek samplers, gave
pulses that were some fraction of the supply voltage, half maybe. The
Zetex things really turn on basically saturate, when they fire.
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com