IGBT failure in xenon flash bulb circuit - Page 1
Forum section: electronics / projects

author: davidb
author_rank: Contributor
timestamp: November 26, 2020, 08:32:38 am
content: Hi folks, I'm having trouble with a new design, that echos this thread pretty closely:https://www.eevblog.com/forum/projects/xenon-flash-lamp-circuit-igbt-failure/I'm using the same reference design, albeit with some different components.IGBT:https://www.infineon.com/dgdl/Infineon-IGB50N65S5-DS-v02_02-EN.pdf?fileId=5546d4625e763904015ec81bbc6f2fecDriver:https://www.digikey.com/en/products/detail/ixys-integrated-circuits-division/IXDI609SIATR/2521825Voltage: Right now they're using ~350v, though the cap charger is configured to support 500v, I doubt they'll go that high.Trigger cap: I'm not sure why I chose to use a 0.1uF on the trigger coil, other than I had it in stock already. Would a smaller one make any differenceThe cables to the AD600 bulb are on the order of 15-19" long (!!), and once they leave the enclosure are within a shielded cable.My client needs to be able to flash the bulb at 3 to 5Hz, for quite a while at a time. As such, I have an adjustment in the micro-controller to set the duration that the IGBT is allowed to conduct, to preserve voltage on the main capacitors and maintain the high flash rate.Problem: At low enough gate pulse width durations (~200uS), the IGBT fails. I'm starting to think that this is due to an inductive kick from inductance in the wiring. At longer gate pulse width durations the IGBT will survive pretty much indefinitely (at least to the limit of our testing thus far).The other thread suggests some sort of snubber; I'm assuming across the collector-emitter on the IGBT. Is this as simple as adding a TVS with a breakdown voltage a fair bit higher than the operating voltage? ie, the Littlefuse P6SMB530CA (500v breakdown, 725v max clamping). Keep in mind that during use, this will be getting hit pretty hard very frequently.Or is a freewheeling diode or RC snubber a better choice? I just now realized that I already have D1 (600v, 1A) on hand I can put on the board for testing...Thanks for any insights

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 26, 2020, 09:58:15 am
content: If you scope the collector with a x100 probe as you adjust the pulse length, that should tell you a lot about what's happenning.Most likely inductive kickback - as well as snubbers, it might be worth looking at slowing down the turn-off

author: Wolfram
author_rank: Frequent Contributor
timestamp: November 26, 2020, 10:51:56 am
content: My bet is that IGBT damage is due to overvoltage on turn-off, due to the inductance of the current loop that the IGBT is interrupting. This would also explain why it only dies when interrupting the pulse early, as the current will be highest then.To solve this, you need to provide a second path for this current to flow, ideally as close to the IGBT as possible as any stray inductance between the IGBT and the clamping can also develop voltage due to dI/dt. A D+C||R snubber could work, as long as you dimension the diode to have a peak current handling capability in excess of the load current, and the capacitor is big enough to absorb all the energy stored in the stray inductance without charging up beyond the IGBT voltage rating.A simple clamp diode across the flash lamp, placed close to the bulk storage cap and IGBT, could potentially do the bulk of the clamping. Here it's critical to make the loop between the caps, IGBT and diode as low inductance as possible.A TVS might not be suitable, as the peak power it would need to handle would be pretty high. Hundreds of amps at 500+ volts is orders of magnitudes more than the common ones are rated to handle.Whichever solution you go for, make sure to verify the overshoot under worst case conditions. The bulk storage capacitor ESR will vary significantly with temperature for example.

author: davidb
author_rank: Contributor
timestamp: November 26, 2020, 08:52:42 pm
content: Quote from: mikeselectricstuff on November 26, 2020, 09:58:15 amI think the collector was the only place I didn't scope on the prototypesI'll definitely do that after I get the IGBT replaced and continue my testing.By slowing down the turn off, do you mean use PWM to phase off the igbt, instead of a single turn off? I can definitely look at doing that, at a much higher frequency for 10's of micro-seconds.Wolfram, do you know of any resources that would help me properly size the D+RC snubber?Thanks for the replies

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 26, 2020, 11:00:53 pm
content: Quote from: davidb on November 26, 2020, 08:52:42 pmNo, just some resistance/.capaicance on the gate to slow the turn-off slightly

author: davidb
author_rank: Contributor
timestamp: November 26, 2020, 11:16:53 pm
content: Quote from: mikeselectricstuff on November 26, 2020, 11:00:53 pmOh, gotcha. I have a 10ohm on the gate now. It would be easy to increase that a bit. Thanks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 27, 2020, 02:55:36 am
content: What driver voltage?That gate resistor looks awfully low, and the IGBT isn't rated for much peak current. Do you know that the current is limited properly (by ESR, ESL)?The usual type of IGBT used for interrupting photoflash discharge is a small SMT device rated for something like 400V 400A, and several microseconds turn-off.The switching loss is intentionally very high, because the PRF is very low; in a camera, seconds between shots. The slow switching avoids having to add a snubber and all that.You may have trouble running at even the PRF given, and so need a significantly larger IGBT to stay within ratings -- I don't know of any pulse rated IGBTs in that voltage, current and speed, you'll probably end up with a huge 100 or 200A type. (PDP driver IGBTs may be applicable, if they're still available. Tend to be just a tiny bit low in voltage though.)The problem with driving a large switching IGBT, quickly, is the ESL, and yeah, that'll gladly nuke the thing. Put a RCD snubber or TVS from emitter to collector, clamp the voltage below ratings under worst case wiring condition and peak current.Tim

author: davidb
author_rank: Contributor
timestamp: November 27, 2020, 07:43:03 am
content: The igbt driver gets the board input voltage, which is 12-16v.I'm actually not sure what is limiting the currentI'll experiment with the hardware I currently have, but if that doesn't work out for some reason, it may be best to move towards the igbt in the original app note:https://www.digikey.com/en/products/detail/on-semiconductor/TIG065E8-TL-H/5213418I chose the igbt I'm currently using because of the higher CE voltage, and the higher pulse current.I was wondering why it made a big deal of having aslowerramp on the turn off in that app note. I now know the reason is to stretch the shutoff time to avoid needing a snubber/reduce how hard it turns off.Thanks again. I now have several paths forward to solve this problem

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 27, 2020, 08:13:56 am
content: Quote from: davidb on November 27, 2020, 07:43:03 amOh, it was only 150A! Then the one you have should be fine, so long as dynamics are controlled similarly (ESR + ESL).Tim

author: davidb
author_rank: Contributor
timestamp: November 27, 2020, 09:24:35 am
content: Quote from: T3sl4co1l on November 27, 2020, 08:13:56 amI gotta say, as frustrating it is having hardware failing, this has been fun to learn about, and I'm looking forward to making changes and seeing the resultsFor posterities sake I'll plan to post oscope screenshots as I work through it.

author: davidb
author_rank: Contributor
timestamp: November 28, 2020, 09:05:31 am
content: I got the igbt replaced, and everything hooked up to the scope tonight. The results... aren't what I expected.The PC capture program for my scope (Rigol DS1054z) doesn't want to work right now, so I don't have screenshots yet. I'll refer to the test points as they're labeled in the schematic in the first post.Immediately after firing, U8 goes to -40v, and U3 goes negative to about -100vAs the igbt turns off with the pulse duration near where it dies, and a Vcap of 340v, U3 spikes to 140v after 5us, then goes to 100v as it starts to recharge back to 340v.U8 however, spikes to 550v in the first 500ns after firing, then rapidly settles down and starts charging back up too.At longer durations, the spike isn't there on U3 or U8.I only have one more igbt on hand, so I don't quite want to do a suicide capture, yetIt's late here. Tomorrow I'll try increasing the gate resistor a bit, and see how it responds.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2020, 11:34:12 am
content: Show a picture of your layout and probing setup.I think you will find currents of hundreds of amperes, switched on microsecond time scales, are quite happy to induce substantial voltages in spaghetti wiring...Tim

author: jonpaul
author_rank: Super Contributor
timestamp: November 28, 2020, 11:54:45 am
content: Need the exact type of wires to the lamp, and trigger coil config.Series injection or third electrode?Cables are twin, coax, etc?The loop area enclosed by the current path cables and lamp, will determine inductanceFigure about 1 uH ? See formulas....Jon

author: davidb
author_rank: Contributor
timestamp: November 28, 2020, 09:11:41 pm
content: Here's a picture of the board and the cabling. The purple board is where it goes through the enclosure. I tried to get a single cable through the enclosure, but these are going on tractors, so the client wanted to be able to easily swap the outside cable if it gets caught on something and damaged.There are some ground points on the bottom edge near U8/U11 that I'm using to ground the probes at.My testing last night did not have the intermediate cabling with the purple board. Just the long cables direct to the board (worst case, right?)Outside the enclosure the cables are wrapped in braided shielding, then shrink tubing.lamp wires:https://www.digikey.com/en/products/detail/mueller-electric-co/WI-M-14-10-2/9675952trigger wire:https://www.digikey.com/en/products/detail/pomona-electronics/6733-2/737852Trigger coil (no longer in stock...):https://www.digikey.com/en/products/detail/excelitas-technologies/ZS1052-AC-H/5885884If there's a better way to get the wires through the enclosure, I'd love to hear it. I didn't have any luck finding a plug that met the voltage and amperage requirements.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 28, 2020, 09:40:25 pm
content: Oh, so it's just a plain old strobe fixture for a moving vehicle? ...Why reinvent the wheel?I see what may be stitching vias, is that the case?Oh, U for test points, that's weird. Okay, bottom edge between C1 and D2, got it. Should be inboard of most switching currents, if the rest of the plane is reasonable.I don't have a problem with e.g. 600V connectors carrying stuff like that. I expect it's not going to start a fire (discharging those capacitors will give a hearty spark, but not a sustained arc?), and the trigger is intermittent -- mains connectors deal with transients of some kV by design.May also find it useful to put the trigger coil stuff out with the tube, saving one connection and not needing high voltage withstand at all. The lamp module then becomes a little more expensive, but it can be placed much farther away -- if that's of interest.Tim

author: davidb
author_rank: Contributor
timestamp: November 28, 2020, 10:46:57 pm
content: Why? It's what the client wanted, of courseI know they evaluated some commercial offerings, but apparently, they didn't fit their flash rate or packaging requirements.Yes, there are stitching vias tying the large open areas together. The shield connection has an isolated trace around the top edge of the board back to the power input.U for test points, yea, that's pretty bad. SorryInteresting thought about moving some stuff to the bulb. I'll have to think about that.

author: moffy
author_rank: Super Contributor
timestamp: November 28, 2020, 10:51:29 pm
content: What about a fast diode between emitter and collector(in parallel with the body diode) to limit those negative excursions at U3?

author: jonpaul
author_rank: Super Contributor
timestamp: November 29, 2020, 10:00:56 am
content: Just Use commercially avail vehicle strobes for 12V or 28V, cheap and self contained. No need for 2 separate units. Bad idea.Ignitor MUST be at flash-lamp for safety and full voltage pulse, any wires will load itThe cheap Trigger transformes are from China, long lead delivery and unreliable.We made our own trigger transformers.Jon

author: davidb
author_rank: Contributor
timestamp: November 29, 2020, 06:00:36 pm
content: Do you have an example of a vehicle strobe? I'm not following...I am liking the idea of moving the trigger coil to the bulb. The harness would just need 300v, collector, and ground (for the small cap on the trigger coil). Then all HV would be only at the bulb, and with only minor changes I can make the current hardware work with it for testing.I would be surprised if this product moved hundreds of units, so I'm not sure if it's worth building my own transformers? Though I am interested in the process.I discovered I ran out of the high voltage diodes, so I had to order some more. It'll be a couple days until I can do some more testing.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 29, 2020, 07:12:23 pm
content: You absolutely need the trigger coil close to the tube. It relies on having a fast risetime to capacitively couple through the tube, and the high voltage spike will cause a lot of EMI if the wire isn't as short as possible.

author: jonpaul
author_rank: Super Contributor
timestamp: November 29, 2020, 07:50:08 pm
content: Hello again DavidB: I made my first strobe in perhaps 1960..1963. Worked on cinema lights with up to 12 kw and 55 kv ignitors.....1/ Design: It is a well known circuit. see attached2/ Stock vehicle strobes : ~ $25http://www.seco-larm.com/SL-126Q-A3/ Trig location: Not a "like the idea" BUT a required and standard good design. EVERY remote trig has problems!Your pulse is ~ 5-15 kV and Trise ~ 50 - 200 nS. Any load capacitance degrades it.4/ Trig coils: millions from China, global logistic causes long leadtime. Check every disty: Mouser, Frys, DK and surplus houses for in stock coil.Hard to wind and impregnate without special winding machine and impregnation. Coil forms and ferrite slugs and fine wire are needed.5/ For a few 100 ..few 1000 you are reinventing the wheel, just search harder and get a stock strobe for the customer.Bon chance!JonPS: Beware of liability in HV devices, eg a farmer fools with the "bulb", and the HV pulse causes accident or he has a pacemaker.....

author: davidb
author_rank: Contributor
timestamp: November 29, 2020, 09:12:02 pm
content: oh, wow, I apparently never mentioned that this is mated with a camera, and the flashes need to be timed to the shutter. That's my badThere's a camera module and the flash module stacked near each other (properly shielded/etc). Then the bulb is remote and pointed at whatever they're taking pictures of.I hear you on the remote trigger though, and will definitely make that change

author: jonpaul
author_rank: Super Contributor
timestamp: November 30, 2020, 10:42:52 am
content: DavidB: You waste time by not revealing the ENTIRE REQUIREMENT in your original post.A more descriptive title would have been:"Xenon flasher, with sync for photography"A simple sketch of THE ENTIRE SYSTEM, power source, flasher, camera, packaging, etc would have been much easier than so many emails due to lack of info.Note that flash sync is not a trivial issue as the xenon duration is 10-100 usec and camera shutter time normally longer.As you fail to mention the flash rate, camera type, method of sync connection or any other info, I cannot comment further.Good luck,byeJon

author: LaserSteve
author_rank: Super Contributor
timestamp: November 30, 2020, 05:14:45 pm
content: Your missing a few supporting parts, see the original Fairchild app note for needed diode.https://www.onsemi.com/pub/Collateral/AN-9006.pdf.pdfWhat I'm about to tell you is lore, not math... but it gives you some things to look at...Trigger currents need to launch and return, even when applied to outside the lamp.. Capacitor currents need to launch and return. You have to keep track of that.If the circuit is not carefully set up for correct damping, you can get a few reverse voltage swings as the lamp dies down. Bye Bye IGBT.You can also get trigger pulse into the IGBT without proper snubbing, capacitor bypassing, or the wrong layout. Usually a high voltage plastic film or oil filled paper cap goes across the switch for sanity reasons. Then one across the HV supply and storage cap, to allow trigger to return to HV without puncturing the electrolytic or switch. But I work on industrial flash, stroboscopes, and lasers, not automotive, alarm, or strobe stuff from that novelty store in the mall..I can't post you a copy, but if your flash rate ever has to increase take a look atReview of Scientific Instruments 69, 325 (1998);https://doi.org/10.1063/1.1148519Both of these allow you to trigger as well as cut the flash duration down using a series IGBT.I have 20 years of maintaining Krypton arc lamp and xenon flashlamp pumped lasers that cost between 40,000 and 250,000 Dollars each and have to run for years / decades with no PSU issues. Trust me, I know my lamps. We used SCRs for lamp commutation and triggering, as well as simmer currents to keep the lamp ionized between flashes. While I can't see simmer for an automotive application, it sure does make strobing easy. I can see switching to series injection ignition transformers rather then the traditional trigger coil, if your lamp is at the end of a cable. That way the lamp dissipates the trigger pulse energy. No one runs a HV trigger pulse more then a few cm , unless they use series injection.For a small series injection transformer, a simple toroid works or ferrite rod works, I've done that in my own designs for the lab. Two turn primary for the trigger cap to discharge into, twenty, thirty turns on the secondary, with a wire size big enough to carry the lamp current, would be OK at the few joule level. Designed to be resonant with its load. Ok, so that requires a larger trigger cap energy, so what?Often has a HV ceramic cap across its secondary to "ring" it at the desired 100 Khz to 1 Mhz...I've also used and worked on systems that use low pass filters to keep the trigger pulse out of the commutation electronics and storage caps. If a IGBT was used, it was in the high side, and had a pulse forming networking and snubbing around it.I think your a long way from a production layout. Take a look at Whelen's aircraft strobe drivers and see what your doing wrong. Those and tower warning flashes both run the lamps at the end of long cables, which requires a lot of extra work to get right.I think you might find a small series air core inductor between the cap and the lamp will help too. Reduces Di/DT through the IGBT. Also provides some damping while it slightly to grossly lengthens the pulse width.Series fast recovery diodes that will work in a lamp or arc application will require outside the box testing.see attached...Your also looking for an ancient book entitled:Electronic Flash, Strobe, by Harold Edgerton. Preferably Third Edition, MIT Press, publisher.Taking a photoflash topology to a high rep rate generally means looking at some old Honeywell "Strobonar" quenched or SCR commutated flash designs to learn how to manage flash energy using SCRs and energy recovery circuits.The patent server is your friend.Invest in a known good, fast photodiode (Thorlabs DET-10A) and watch your intensity profile. Think of it as the poor man's Rogowski transformer.SEE ATTACHED FILE for the basics.They are Excelitas now...The cheap alternative to IGBT cutoff of the flash is a separately triggered shorter flash tube. Known as a "Quench" tube.Amglo might be of some assistance in design and transformer help:www.amglo. com, or Excelitas,www.excelitas.comParts and expertise options are often NOT on websites in production grade strobing. Most lamp companies have greybeard apps engineers.I,like JonPaul, have to put my time where it belongs, I'm done with this thread. Good Luck.Steve

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 30, 2020, 09:57:00 pm
content: Oh and... two capacitors in parallel? If one has the two ohm ESR needed to limit peak current to 150A, well, two in parallel ain't gonna cut it and you need a bigger IGBT!And if the ESR is lower, and whatever ESL is doing we're still not sure, it will be even higher.Tim

author: davidb
author_rank: Contributor
timestamp: November 30, 2020, 10:00:53 pm
content: Yes, I apologize for not sketching out the entire system. Reading my original post again, I can see how the "3Hz to 5Hz for a while at a time" could be interpreted as needing a strobe light. That is the maximum flash rate as commanded by the camera module. There is a micro-controller on the flash board that takes the signal to fire, then drives the igbt gate driver for the designated pulse width time.While the rest of the information may have been helpful (sync connection/camera type/power source), I saw those as not really relevant, since the problem is isolated to this circuit board. That is, it needs to be able to flash the bulb at short durations without killing the igbt. We'd have trouble with the igbt regardless of how we were triggering it, or for what use case. All that being said, I should have included more system information.LaserSteve: Thanks for thegreatinformation. It looks like that's exactly what I need. I really appreciate it.

author: davidb
author_rank: Contributor
timestamp: November 30, 2020, 10:09:08 pm
content: Quote from: T3sl4co1l on November 30, 2020, 09:57:00 pmWhich caps are you looking at? C2/C3 are decoupling for the igbt driver. The bulk caps are in series, and are 330v/330uFhttps://www.xenonflashtubes.com/photo-flash-capacitors/330v-330uf-photoflash-capacitor-pulsed_95.html, datasheet:http://www.glancap.com/web/viewerPDF.asp?Filename=/uploadimg/PF%20Series.pdf(they are on a tiny board to make them right angle, so they're not on the schematic I posted anymore...)More info I now realize was missing from the original post

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 30, 2020, 10:53:22 pm
content: Oh, well, that's not what I had guessed from the 350V setting, or even the 600 or 630V ratings......Does it fire at all, testing with a smaller tube or something?No ESR rating, anyone's guess what peak current is. Tan delta is pretty low, looks suspiciously like a regular snap-in capacitor if anything, and those are very low ESR (capable of quite high currents, but maybe not reliable, i.e. without mechanical fatigue).If you're getting reversal from the trigger, you can add some R or L in series to it, to increase the impedance without significantly reducing the power delivered by it (how much, depends on the transistor, the transformer characteristics, and what peak output is required; Steve and JP probably have something to add here, I can only guess). Or even put it on its own board, with a dedicated transistor driven in sync with the main.A current transformer will be the easiest way to measure load current without error from induction. Downside is you need a rather high ratio. A high-mu ferrite toroid with a few hundred turns on it does a great job. A burden resistor of a few ohms will give plenty of signal, and the overall gain is simply calculated. (A 500 turns winding divides load current by 500, so a 0.5 ohm load gives a 1V drop from 2A on the secondary from 1000A on the primary for example, or 1V/1000A gain.)If the collector voltage really is reversing (and it's not an artifact of induced noise or ground bounce, say), then a diode will help; you may also find it expedient to get a co-pack IGBT, the ESL between IGBT and diode can't be any better than that. And yes, a TVS from GND to collector will clamp overvoltage, can't really get hundreds of volts TVSs but a series chain of a few 100-200V types (SMCJ150A, et al.) will do. Choose TVSs such that, at peak load current (whatever it is -- you'll have to measure, or calculate from the RLC equivalent of the circuit, which is still missing here), the peak voltage is just within the IGBT rating.MOVs can be used here as well, but their peak to nominal voltage ratio is higher, i.e. they're "softer", and you may not be able to clamp the peak current while also handling nominal voltage, at least not without getting an obnoxiously large IGBT (1200V or more?).Tim

author: davidb
author_rank: Contributor
timestamp: November 30, 2020, 11:12:24 pm
content: Yes, it fires just fine, as long as I don't have the pulse duration too short. At one point I had it test firing at 10Hz for several minutes with a small bulb. The real bulb we're using now is pretty bighttps://www.amazon.com/Godox-Flash-Witstro-Speedlite-AD600BM/dp/B01I9JU1Y8/ref=sr_1_3It's been surprisingly hard to find photo flash rated capacitors, so I went with the only ones I could find (assuming they aren't lying...).I'm using the LT3750 to charge the caps. The power input eventually will be Lipo batteries, I believe. Right now it's just a bench power supply.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 01, 2020, 12:40:59 am
content: Ah, a spiral lamp. Not known for withstanding high rep rate service, but far better then loop shaped lamps for handling the shock wave and heat . Good for achieving uniform illumination with the right reflector.A few things more come to mind. Let me play lightning empiricist. (Sorry Bob Pease, and pun intended) For the small lamps you are using, An air cooled, air cored, inductor in this case means, take a decent diameter enameled magnet wire or something larger and wind it as a multilayer cylinder on a 1/8th to 1/4" diameter (3-6 mm) nail. Remove nail, watch lamp on scope using a reverse biased PD and adjust pulse width to be longer while adjusting turns with a pair of snips. The other variety turns out to be a few turns of #14 OFHC copper wound a few inches in diameter then bound in some way. The later is used for larger lamps where the resulting mag field can take apart your coiled inductor. Yet more advanced is a pulse forming network of a few caps and a few inductors.There are two, maybe three regimes, based on voltage across the lamp. Someplace I have a spread sheet for lamp series element parameters, I'll see if I can PM you with it, but I need to dig through the pile of old laptop hard drives. Might take a day or two to find that. Increasing voltage on the cap while decreasing capacitance makes it easier to fire the lamp , while switching you to a self pinching , self centering, brighter discharge versus a wall guided discharge. That self centering discharge shortens the pulse and gets closer to the single shot implosion energy. Hence the inductor. Ok, so an inch and a half inch long lamp self breaks down at around 1200 volts DC based on my experience, at no current. So there is a limit, the implosion energy and stored heat in the lamp, and self breakdown.Generally I aim for some place between the two, and stay well above the lamp's minimum voltage, so as the lamp ages, I still get triggering. If I really need to ensure triggering to make a professor happy, I use a smaller starter cap with a boost voltage as well as the main cap, or go to simmering. As the lamp starts to "burn in" during use, the emissive coating on the electrode forms 'micro" or "nano" fingers which are what actually emits the electrons, a cloud of point source emitters with high fields, that you might think of.Lowering the lamp's initial turn on pulse energy by varying the voltage wrecks havoc with the thus formed emissive surface, and its lifetime, destroying the emissive coating, which is why we try to keep lamp voltage very constant, instead of changing the charging voltage to change the lamp energy. Simmering at 10s to 100s of mA of DC extends lamp life, and makes the flash energy consistent, which is important in lasers and high speed photography, which is what I did for years for one professor. Then I went off and serviced lab lasers before returning to the Zoo. Forgive the digression, but in my case I'm either designing for rep rate, or a very consistent pulse length of 256 microseconds, which is the upper state lifetime of the laser rod. No sense pumping the rod more once it is already saturated, or the laser crystal can multi-pulse or do the destructive giant pulsing. So my criteria for a good design might be a bit different then a precision camera flash. Hence the invention of quenching or commutating, or changing storage capacitance, to control light emission, with the initial voltage kept constant. So in my case the LC design is for pulse shaping to 256 microseconds (for ND:YAG lasers) , of pulse width, with a long flat topped pulse desirable.Higher pulse energy/ shorter pulse width = color temperature shifting towards blue, which is why older camera strobes had weakly amber filters for color correction.That should clue you in to why your interrupting the discharge, rather then changing pulse energy . This also keeps your color temperature more consistent, which is important for color photography.If you have to do the math, most tubes are filled with someplace between 450 and 740 torr of Xenon, leaning towards higher pressure. It has to be just lower then atmosphere so the sealing tube collapses when they melt it closed, unless the lamp is large, and thus has a metal pinch-off seal. Just an FYI as you get better with this design process.A consistent source of "abusable" quality lamps is Electronic Goldmine. They can be a little slow to ship, but the price is right, and they usually have a good grade cap laying around. They must have a good deal with the Heineman division of Excelitas to keep them stocked with lamps. Borosilicate lamp = cheap, and moderate energy/rep rate. quartz lamps are for higher rep rates, longer lifetimes, and higher energy, but the cost can be staggering and the UV emission climbs. For some reason right now they have a handful of quench tubes in stock, and I bought a handful for playing.B&H photo can be a consistent source of lamps, too...J. H. Goncz is the fellow who worked out much of the lamp current , lamp circuit design and implosion energy math, as well as Dr.(s) Edgerton, Grimes, and Grier (EG&G ring a bell?)If you run Goncz's name and Xenon, through citation indexes useful PDfs often appear without access to a university library. Edgerton's book (Abe Books and Amazon can be a source) covers much of what you need, but IGBT's didn't exist yet.I hated math much of my life, and as a busy technician at a university, I often find cut and try on the bench to my liking after using a napkin at lunch for the CAD and Math. After switching departments from a more industrial research oriented organization to a more engineering/teaching organization, I now love math and do more of it. So, series L that comes to mind at first guesstimate is 10 to 100 microhenries depending on the tube. Small Camera Flashlamps use a coiled inductor as described with some sort of sintered powder core, in the form of a short right circular cylinder, just a short sintered rod about 12 mm long and maybe 4 mm diameter. Much larger lamps use big inductors and layered cores that are probably beyond the scope of this discussion.OK, a bit about PDs for your scope and enlightenment. The Det 10 uses a reverse biased Photodiode of around 1 square mm, reverse biased between 5 and 9 volts depending on model, with a decoupling cap, 100 mA regulator, a reverse protection diode, and a protective resistor and a bit of stripline for the speed that it provides. Schematics are out there and Thorlabs sells the same PD for about 20$ if you have to roll your own, rather then pay 150-250$ for one. I specified the DET-10 model because it is bulletproof , uses a cheap, long life battery, has a BNC, a mounting hole, and is inherently shielded. Full speed comes when the 50 ohm termination on your scope is active.There is a few years of issue of the GE or Westinghouse SCR handbook that covers the calculation of the pulse surge currents through the semiconductor. I'll see if I can find it in the home piling system.See page 6 of attached for a good one page design summary. With that, Tim should be able to get you into the ballpark on IGBT selection.Math from my good friend Sam and his friends, including one spreadsheet.https://www.repairfaq.org/sam/lasersps.htm#spsdls1more math:https://www.repairfaq.org/sam/laserssl.htm#ssleqsDesign Lore:https://madengineer.ch/blog/2015/08/01/diy-igbt-controlled-1000ws-flash-unit/(He turns on the IGBT prior to trigger )http://repairfaq.cis.upenn.edu/sam/strbfaq.htmhttp://donklipstein.com/donflash.htmlheavier reading, three of them irrelevant, but looking the references for the papers can clue you in, if you like MATH:J. H. Goncz, (John) “Resistivity of Xenon Plasma,” J. Appl. Phys. 36, 742–743 (1965). 2. A. Marotta, R. M. O. Galvao, “Anomolous Plasma Resistivity in Prepulsed Flashlamp Discharges,” Appl. Phys. Lett. 33, 280–281 (1978). 3. J. T. Lue, D. Y. Song, C. K. Yeh, “The Plasma Z-pinch Effect on the I-V Characteristic of Fast Discharge Flash Tubes,” J. Appl. Phys. 51, 4626–4630 (1980). 4. W. L. Lama, T. J. Hammond, P. J. Walsh, “Theoretical Model of Visible Radiation from Rare Gas Flashlamps,” Appl. Opt. 21, 654–659 (1982).   

author: LaserSteve
author_rank: Super Contributor
timestamp: December 01, 2020, 02:22:03 am
content: Quickie online lamp calc...https://www.fenixtechnology.com/fenixcalc.htmlNow I really have to quit replying.Steve

author: davidb
author_rank: Contributor
timestamp: December 05, 2020, 09:07:49 am
content: I finally have some results: The primary culprit I believe was the small gate resistor. Turn off time was ~163ns, and at the short pulse duration, caused a spike to 764v on the collector at turn offThis of course exceeds the igbt's Vce max of 650v, and it dies.Yellow channel 1 = Collector, right at IGBTLight blue channel 2 = testpoint U8 (trigger coil/capacitor)Magenta channel 3 = IGBT gate, testpoint U6Dark blue channel 4 = IGBT driver input (for triggering the scope), testpoint U12While waiting for more diodes to arrive, I started testing by changing the gate resistor to a 33ohm, then 78ohm. At 78ohm, the turn off time is 1.5us, and the spike on the collector at shutoff ismuchsmaller. I kept the pulse duration high, since I didn't want to kill components until more showed up.But, I still had bad ringing on testpoint U8, hitting ~-100v.Adding a freewheeling diode from the collector to ground eliminated a negative excursion at the collector on the rising edge of the bulb flash, but did nothing for the ringing on U8. (this capture shows the negative spike on the collector (yellow trace) from not having the freewheeling diode in place).I then added a diode in parallel with C1, and that caused the ringing to stop completely at bulb activation.At this point I started testing with short duration pulses, and the igbt was surviving them. But I didn't know which of the three changes did it. So I went backwards, taking off the parallel diode on C1, taking off the freewheel diode on the collector, and it continued to survive. It was only after I went back to the original 10ohm gate resistor that it died immediately, for the reason shown in the first attachment.Earlier in the thread, a turn off time of "several micro-seconds" for the igbt was mentioned. Should I increase the gate resistor size until I get to 2-3uS, from my current 1.5us with the 78ohm resistor?Is the diode in parallel with C1 the "correct" way to fix that ringing? It sure doesn't seem like it... I'm planning to move to the circuit found here at any rate.https://www.onsemi.com/pub/Collateral/AN-9006.pdf.pdfLaserSteve: Thanks for the long replies. I've read through them a couple times, and I'm still pulling information out. There is a lot more to flash bulbs than I even considered before starting this project."The more I learn, the more I discover I didn't know"Thanks for all the repliesedit: huh, I thought the images would be inline?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 05, 2020, 10:43:27 am
content: How about a diode in series, between trigger coil and collector?Or ESR in series with C1, or in the same location as above? I'd have to know the transformer parameters to give a good guess, but a starting point might be 1-100 ohms.Or maybe your C1 is too large for the transformer, and a more suitable value might be chosen.Reverse bias (if it is indeed ringing as shown, and not an artifact of interference) suggests the trigger coil is dumping more current than the lamp is, which seems rather unbelievable. But Idunno, the lamp should take a good few microseconds to start up. Could always just drive the gate even slower? (Can use a parallel resistor and diode, to speed up turn-off while keeping turn-on slow.)Have TVS diodes been ordered?TimP.S. Yeah, inline attachments broke weirdly as of some months ago (or was that closer to last year by now, I forget). Attachments have always been inlinable anyway, just by manual process: hover over the un-expanded thumbnail, copy its link address, then edit post, and paste that between img tags.I don't have a clue why the plugin isn't just a macro for doing that.