Very high voltage BJT needed - Page 1
Forum section: electronics / projects

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 01:10:07 pm
content: Hi,I'm working on a project which requires a very high voltage BJT. The highest I have seen are 800V, but I need about 1kV, preferably more than that. Unfortunately I have not bee able to find anything from usual suspects like ST, ONSEMI, Fairchild and the like.The only other thing that is required of the transistor in question is for it to be able to handle about 4-5W of power. It has to be a BJT, IGBTs and MOSFETs are not an option.Do you know any parts that fit those requirements?

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 01:17:49 pm
content: I typed "1kv bjt" into google and the very first hit had an ONSEMI part number and datasheet.

author: mzzj
author_rank: Super Contributor
timestamp: November 12, 2015, 01:18:53 pm
content: Darlington ok?http://www.digikey.com/product-search/en?pv814=28&pv814=152&pv814=15&pv814=141&FV=fff40015%2Cfff80078&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

author: Srbel
author_rank: Frequent Contributor
timestamp: November 12, 2015, 01:22:26 pm
content: http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000004650&sort=P_PRICE&pageSize=25&showResults=true&pf=110000492,110000676,110002775,110002776,110002778,110002800,110007522,110007527,110007531,110007699,110015165,110015335,110015368,110015421,110015422,110022493,110030220,110030404,110030406,110032611,110033543,110037410,110037429,110037431,110037450,110037489,110037521,110037592,110046151,110047927,110048549,110052207,110060920,110061074,110066637,110066638,110070090,110075065,110075150,110075346,110075368,110078483,110079931,110080444,110083936,110084793,110086199,110091762,110095817,110099503,110101206,110104118,110105136,110109160,110114652,110115437,110116863,110117963,110118046,110118368,110119254,110328782

author: mzzj
author_rank: Super Contributor
timestamp: November 12, 2015, 01:22:50 pm
content: Quote from: Fungus on November 12, 2015, 01:17:49 pm1000v rated for Vcb or Vce?

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 01:25:45 pm
content: Quite often it turns out, that the advertised voltage is VCB, not VCE. The STP03D200 quoted above has "2kV darlington transistor" as the datasheet headline, but it turns bout that VCB max is only 1200V.Anyway, this might be an option. The high current gain in this situation is not an advantage, but rather a problem what would have to be worked around (part of the circuit behavioir is that the collector current will get limited due to low hfe). High gain would also make it harder to achieve stability of the control circuit. Nevertheless, it is some option if nothing else is found.

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 01:29:27 pm
content: Quote from: Srbel on November 12, 2015, 01:22:26 pmThe steady state withstand capability is only 450V. 1.05kV is some shady peak rating.

author: mzzj
author_rank: Super Contributor
timestamp: November 12, 2015, 01:31:38 pm
content: Quote from: poorchava on November 12, 2015, 01:25:45 pmMaybe ST's ESBT transistors would work in your application. Just turn on and ignore the mosfet.?In any case you have very limited choices with possible problems of single supplier.

author: Srbel
author_rank: Frequent Contributor
timestamp: November 12, 2015, 01:32:30 pm
content: Yeah, that 1KV one, but this one has 800V sustainable Vce:http://www.farnell.com/datasheets/1700043.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2015, 01:32:47 pm
content: Is this for linear application...Tim

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 01:37:07 pm
content: 800V is not enough. It just blows up during tests. Currently we have this in the circuit:https://www.fairchildsemi.com/datasheets/KS/KSC5603D.pdf.Single supplier is not a big problem. In general my company uses a lot of exotic components, most of which there is only one supplier of. We have this handled.And ya, this will work in linear mode. Sorry, can't be more specific than that. In general the circuit works very well in normal conditions, the transistor blows up from transients and surges on the input voltage. The continuous rated input voltage is 700V DC, so an 800V rating on the transistor was already on the thin side. We thought we could build an adequate input protection, but so far he haven't been able to.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2015, 01:41:39 pm
content: Look, you simply don't use BJTs for HV linear. That's 100% MOSFET territory.I suppose maybe an SiC BJT would be okay, but those are just as rare and expensive.Tim

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 12, 2015, 01:45:46 pm
content: Hi,If you are operating in the Linear region, you need to do some research on 'Second Breakdown region'. BJT do not like high voltage and low currents.Have you considered placing the BJT and a MOSFET in series? (cascade configuration). The MOSFET will share the voltage.Regards,Jay_Diddy_B

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2015, 01:46:17 pm
content: Quote from: mzzj on November 12, 2015, 01:22:50 pmhttp://www.onsemi.com/pub_link/Collateral/MJW18020-D.PDFDepends on which version of 'Vce' you prefer

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 12, 2015, 02:07:15 pm
content: Hi,If you look at the data, the MKW18020 is barely 450V:Jay

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 02:18:00 pm
content: Quote from: T3sl4co1l on November 12, 2015, 01:41:39 pmBJTs have one advantage: the hfe sets a hard limit on the collector current. Limiting Ib in a permanent fashion (eg. resistor in series with base) ensures that no more than Ib * hfe will flow through the collector, therefore the crappy hfe of high voltage power transistors is an advantage. I regret that I can't take a photo of the small bucket of exploded MOSFETs that died during experiments

author: deadlylover
author_rank: Frequent Contributor
timestamp: November 12, 2015, 02:32:07 pm
content: The Toshiba 2SC4686A has a Vceo of 1200V and Vcbo of 1500V. Out of production for a few years already though, but maybe you can find a supplier that still has some lying around?One of my favourite parts for electrostatic headphone amplifiers, I have a large amount stored for a rainy day.Postage (well...everything) is bloody expensive here in Australia ($50-$100 for <500grams!!!), otherwise I'd send you a bag of 50 to play around with.

author: N2IXK
author_rank: Frequent Contributor
timestamp: November 12, 2015, 03:10:50 pm
content: 1500V+ BJTs were commonly used in the horizontal sweep output stages of CRT based TVs and monitors. The market for them probably contracted pretty dramatically when LCD panels took over.

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 03:14:32 pm
content: Sadly, NRND stuff can't be used. That's a commercial project and I'm gonna need like 10k of those over next 5 to 10 years or so.Sent from my HTC One M8s using Tapatalk.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 12, 2015, 03:21:20 pm
content: Stack a few 450V devices in series?Steve

author: dom0
author_rank: Super Contributor
timestamp: November 12, 2015, 03:29:05 pm
content: 2SK1317

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 03:34:02 pm
content: Quote from: dom0 on November 12, 2015, 03:29:05 pmThat's a MOSFETSent from my HTC One M8s using Tapatalk.

author: dom0
author_rank: Super Contributor
timestamp: November 12, 2015, 03:35:56 pm
content: So what? If you need a 1+ kVBJT you're doing something wrong with your design.Quote from: N2IXK on November 12, 2015, 03:10:50 pmThey were only meant for switching, they tend to break down at about 1 Watt of power in linear mode.

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 04:06:39 pm
content: Sorry, can't do neither of those because of NDA. The application is rather unorthodox. If I could have used a MOSFET, I would.Sent from my HTC One M8s using Tapatalk.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 12, 2015, 04:23:12 pm
content: Lots of high voltage BJT for old TV sets are available. Usually something liek 1500/700 V rating for V_CB / V_CE. You get them rather cheap as leftover. Look for something like BU208, BU508 and newer.A Cascode of a BJT and FET mit be an option in many cases. The FET could also be a SiC or InP J-Fet, so you may not need a separate gate volatge.

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 04:35:37 pm
content: Exotic semiconductors can be an option if the price is not too exotic. The end product is not an "absolute minimum cost crap" like white goods or something, but it is BOM price conscious, so to speak. I guess the maximum cost of the transistor at 1k/year should be limited to 4 bucks or thereabouts. I think this pretty much rules out GaAs, SiC, InP, GaN and the like.Sent from my HTC One M8s using Tapatalk.

author: dom0
author_rank: Super Contributor
timestamp: November 12, 2015, 04:35:57 pm
content: I would have to look the exact number up in my lab journal, but the BU 508 (ISC?) failed in the way described above. I suspect that these have very high current density and this leads to especially high second breakdown susceptibility.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 12, 2015, 05:05:13 pm
content: Did you check IGBTs?Fairchildhas some >1kV series.I am not sure of their performance in the linear region, though.

author: kony
author_rank: Regular Contributor
timestamp: November 12, 2015, 05:17:54 pm
content: Any reason for not using cascode stack?

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 05:26:43 pm
content: Ok, I need to watch very carefully what I disclose.The HV source in question a an external voltage rail, which is is DC or rectified, unfiltered AC. AC frequencies can be from <1Hz up to 1kHz or so. The input rail might be anything from few volts DC up to 700VDC with potential to supply hundreds of amps, this also includes all types of mains voltage with all the associated transients, bursts, surges and all that shit. The circuit itself could be described as a very bizarre form of artificial load. The peak current through transistor will not exceed 100mA. Power/heat dissipation/thermal stuff is handled accordingly and is not considered to be a problem. I can't disclose anything about how this is controlled.This is as much as I can disclose. In general changing circuit topology and general principle of operation is not really an option, that is unless we are completely sure that a suitable BJT to use in the current design cannot be found.Cascode means two large devices and this was not and option due to lack of space. Stuff like an integrated ESBT could work though, but would require big changes to the mechanical design.

author: woodchips
author_rank: Frequent Contributor
timestamp: November 12, 2015, 06:25:19 pm
content: Have you tried Westcode (I think, long time ago) who supplied transistors for large lasers?

author: MagicSmoker
author_rank: Super Contributor
timestamp: November 12, 2015, 06:32:54 pm
content: http://www.digikey.com/product-detail/en/STN0214/497-12862-1-ND/3043777Parallel several of them with appropriate emitter ballasting resistors if you really need to run ~100mA in linear operation.

author: nctnico
author_rank: Super Contributor
timestamp: November 12, 2015, 06:38:23 pm
content: Quote from: poorchava on November 12, 2015, 01:37:07 pmThis is a switching transistor so probably completely unsuitable for your purpose. There isn't even a safe operating area graph in the datasheet! I'd try to cascade several transistors in order to divide the voltage and look for transistors designed for linear applications.An appnote about breakdown in transistors:http://www.onsemi.com/pub/Collateral/AN1628-D.PDF

author: owiecc
author_rank: Frequent Contributor
timestamp: November 12, 2015, 06:58:37 pm
content: SiC BJTs:http://www.genesicsemi.com/commercial-sic/sic-junction-transistors/

author: poorchava
author_rank: Super Contributor
timestamp: November 12, 2015, 07:16:09 pm
content: That's actually interesting. I just wonder why they spec Rdson instead of saturation voltage.Sent from my HTC One M8s using Tapatalk.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: November 12, 2015, 08:34:24 pm
content: base current*hfe output current limiting is just not reasonable engineering practiceemitter R degeneration with max base drive V limit to base is however designable, reliableof course the same applies to MOSFET Source R as a current limit although gate Vth range in production gives way more variability than bjt Vbeanother thought: power packaged depletion mode HV MOSFET could make a cascode of small signal packaged bjt with little more extra parts than a gate stopper resistorIxys, Supertex, other make HV depletion MOSFET - some with Idss as low as 100 mA - so "inherently" current limited (if you don't forward bias the gate), more enhancement mode HV MOSFET optionI've personally played withhttp://ixapps.ixys.com/DataSheet/DS98809C(IXTP-U-Y01N100D).pdf- cascode, did blow one up without the gate stopper

author: Someone
author_rank: Super Contributor
timestamp: November 12, 2015, 10:40:27 pm
content: Quote from: f5r5e5d on November 12, 2015, 08:34:24 pmWell put!We've another poster trying to farm out their commercial work and drip feeding their constraints, don't forget to send them the bill

author: owiecc
author_rank: Frequent Contributor
timestamp: November 12, 2015, 10:45:59 pm
content: Quote from: poorchava on November 12, 2015, 07:16:09 pmBecause their output characteristics look more like a MOSFET than a BJT.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2015, 10:54:22 pm
content: I really don't have much left to say then, aside from a meme along the lines of this one:http://memegenerator.net/ZoidbergIf you don'tknowhow to use MOSFETs, you can learn that.Just trying to use something, that's not suited to the task anyway, is idiocy.And anyway, you seem to forget you're talking abouttrusting hFE to protect a commercial product.Talk about terrible!Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 13, 2015, 01:05:23 am
content: BJT?Big Jug Triode. Ah yes!www.radiovilag.hu/images/811A.pdfThis thing can swallow lightning strikes, the only way this will end up in the rubbish is with a hammer.

author: poorchava
author_rank: Super Contributor
timestamp: November 13, 2015, 01:14:50 am
content: Quote from: Someone on November 12, 2015, 10:40:27 pmNot trying to farm out work. I've been working on that project for a year an a half and we just found ourselves in a deep shit. I'm trying to gather different ideas.Obviously the Ib*hfe is not the only current limiting mechanism. There are 3 other protection mechanisms in place plus obvious stuff like fuse, sparkgaps and TVS diodes. Don't you worry.

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2015, 01:47:14 am
content: In these kind of situations it is good to take a step back and get a good grip on what the failure mechanism is. This starts with determining what the worst case scenario is and how to create a test setup which can mimic this worst case condition. From there you have a better understanding what kind of component you need and you can test in a more controlled / reproducable way.Either way in your case it seems you are exceeding the safe operating area of the transistor you have choosen. Finding a suitable transistor will require going through lots of datasheets and compare the SOA limit graphs. Still it seems BJT is not likeley to be found so you might have to reconsider using a MOSFET.

author: dacman
author_rank: Frequent Contributor
timestamp: November 13, 2015, 03:08:24 am
content: http://www.nteinc.com/specs/2600to2699/pdf/nte2679.pdfhttp://www.nteinc.com/specs/2500to2599/pdf/nte2588.pdfhttp://www.nteinc.com/specs/2500to2599/pdf/nte2592.pdfhttp://www.nteinc.com/specs/2500to2599/pdf/nte2593.pdf

author: poorchava
author_rank: Super Contributor
timestamp: November 13, 2015, 05:55:39 am
content: Thanks a lot. The NTE2679 seems like it could do the job.

author: Tim F
author_rank: Regular Contributor
timestamp: November 13, 2015, 06:09:18 am
content: I've always wondered about the reliability of TO220 packages in high voltage applications. Is the creepage distance between adjacent legs not extremely marginal?

author: Srbel
author_rank: Frequent Contributor
timestamp: November 13, 2015, 06:58:20 am
content: I was wondering about the same thing.

author: amyk
author_rank: Super Contributor
timestamp: November 13, 2015, 07:40:31 am
content: Quote from: Alex Eisenhut on November 13, 2015, 01:05:23 amI'm glad I wasn't the only one to think of tubes when I saw the requirements. High voltage, low current is their speciality.

author: oldway
author_rank: Super Contributor
timestamp: November 13, 2015, 08:57:50 am
content: If such a solution should be comercialy possible, the best choise would be the PL509 tube still produced by TESLA.http://www.ges.cz/en/electron-tube-pl509-tesla-GES08201816.htmlIn my opinion, it is the safest way to deal with 1KV 0.1A with linear control.But I know it is not a possible comercial solution.

author: nctnico
author_rank: Super Contributor
timestamp: November 13, 2015, 10:31:04 am
content: Quote from: poorchava on November 13, 2015, 05:55:39 amI doubt it. There is no SOA graph in the datasheet and this transistor is intended for switching/pulsing applications.

author: richard.cs
author_rank: Super Contributor
timestamp: November 13, 2015, 12:02:52 pm
content: Quote from: oldway on November 13, 2015, 08:57:50 amI would agree that it may actually be the best solution but he seems to have tight space constraints. I didn't know the PL509 was still in production... interesting. And he gets an additional "free" current limit - you'll never get more than a couple of amps of cathode emission. Commercial viability is dependent on his size, vibration and cost requirements, together with if he can manage a floating 12 W cathode supply.I've been through all this designing my high voltage bench supply, came up with a viable but quite tweaky (and possibly fragile to transients) design with series-stacked bipolars, but eventually settled on a valve pass element.

author: poorchava
author_rank: Super Contributor
timestamp: November 13, 2015, 12:13:32 pm
content: Yep, tube is not an option. This is a handheld device powered from AA batteries.Sent from my HTC One M8s using Tapatalk.

author: richard.cs
author_rank: Super Contributor
timestamp: November 13, 2015, 12:32:40 pm
content: Then if you must have linear operating bipolars at that voltage then stacking them in series is pretty much your only choice to avoid second breakdown related failures.

author: rsjsouza
author_rank: Super Contributor
timestamp: November 13, 2015, 12:39:02 pm
content: Quote from: nctnico on November 13, 2015, 10:31:04 amI agree, and to add another reason: the 1.5kV is an absolute maximum rate, which is usually not suitable for continuous operation - i.e., it is the maximum the device can tolerate before destruction.I saw many other BJTs that have 1.5kV of absolute maximum, including the famous BU208/BU508 (widely used in horizontal deflection TV sets), but in continouos mode they are less tolerant.

author: oldway
author_rank: Super Contributor
timestamp: November 13, 2015, 12:41:31 pm
content: Quote from: poorchava on November 13, 2015, 12:13:32 pm450V 0.1A = 45W from AA batteries ?450V coming from an external rail....EL34 should be possible: heating 6.3V 1.5AMax anode voltage: 2000VStill in production.With a high power external rail with DC voltage up to 750V, there is a high concern with safety.I do not trust in fuses in such conditions.Semiconductor's solutions seem not beeing reliable nor safe.Safety has a price...9W heating losses !

author: dom0
author_rank: Super Contributor
timestamp: November 13, 2015, 03:49:53 pm
content: Using a depletion mode FET like that is a really clever idea. If you don't mind I'll steal it if I ever need it

author: Ian.M
author_rank: Super Contributor
timestamp: November 13, 2015, 04:25:48 pm
content: +1. .asc file annotated with the orignal explanation and saved.

author: Ian.M
author_rank: Super Contributor
timestamp: November 13, 2015, 05:11:21 pm
content: There was a typo in your part no. You had IHTH in the description and IXTH on the schematic. It looks like it should beIXTH2N170D2.For the TO-247 package, that's nothing that hasn't been solved already. Large area high quality sheet mica under it and an insulated clamping bar across it. The TO-268 would be more interesting to heatsink safely . . . .

author: SeanB
author_rank: Super Contributor
timestamp: November 13, 2015, 05:30:22 pm
content: Quote from: DiligentMinds.com on November 13, 2015, 04:54:43 pmIf you ever took apart a high power semiconductor device like a half bridge there is an aluminia ceramic inside with solder pads top and bottom. As these devices are available in ratings up to 2kV and often guarantee 3kV isolation to the case they might work if you can find them or have some made. Take some aluminia insulators and screen print silver ink on them then bake again.

author: Ian.M
author_rank: Super Contributor
timestamp: November 13, 2015, 05:41:45 pm
content: I wonder how thick an alumina layer the aluminium core circuit board manufacturers can deposit with any of their standard processes? Worst case, it may still be worth using one as a heat spreader and mount it on an insulating layer with generously dimensioned top hat insulating bushes on the bolts attatching it to the real heatsink. Splitting R3 and putting a TVS diode to ground might also be worthwhile to save the input driver in case of MOSFET failure, and that whole lot could go on the aluminum core PCB.

author: oldway
author_rank: Super Contributor
timestamp: November 13, 2015, 06:33:24 pm
content: QuoteYour design is very interesting but when you are dealing with DC up to 700Vdcwith potential to supply hundreds of amps, things can go very bad if something wrong happen.Sincerely, I would never risk to pick up 700V on a high power rail with an handheld instrument relying on a simple mosfet for my safety.

author: dom0
author_rank: Super Contributor
timestamp: November 13, 2015, 06:37:38 pm
content: How about Keratherm green (86/37)? 26 kV/mm, that is, 8 kV breakdown for the standard 0.22 mm thickness. The other Keratherm foils are pretty good, too, but you probably need the 0.5 or 1 mm thickness with them, or need to stack multiple foils.

author: SeanB
author_rank: Super Contributor
timestamp: November 13, 2015, 06:42:12 pm
content: Don't need the nitride, just the regular aluminia sheet will do. Not like you are going to have to handle 1kW of power through a 1cm square here , it would be hand held, for about 2 seconds before turning into a flamelight.wonder if you can get old unused ceramic PLCC packages, as you have both the solderable pad inside and contacts spaced around to solder the pins to. Good heat dissipation there already, even on it's own. Most were quite happy handling 5W of power from the internal chip though you did tend to cook the SRBP boards they were soldered to. The chips were Nokia, made for first generation satellite pay television.

author: poorchava
author_rank: Super Contributor
timestamp: November 13, 2015, 06:56:14 pm
content: QuoteRelax, the enclosure is designed specially for HV applications. There is a really large creepage from anything HV to any place the user can touch. It's a proven design that went through many safety qualifications. The enclosure also guarantees blast containment should anything go wrong and is IP67 rated.Sent from my HTC One M8s using Tapatalk.

author: oldway
author_rank: Super Contributor
timestamp: November 13, 2015, 08:02:59 pm
content: You should also have in serie with the input :- a fuse for 1000V dc...It must be specified for DC because DC is more difficult to interrupt than AC.- a current limiting power resistance.- a diode to protect against reverse polarities.

author: dom0
author_rank: Super Contributor
timestamp: November 13, 2015, 09:19:15 pm
content: Series resistance is sometimes not a good idea, because it can increase the trip time of the fuse significantly (approximately proportional to current squared).

author: poorchava
author_rank: Super Contributor
timestamp: November 13, 2015, 10:00:11 pm
content: Fuse is adequate. 32x6mm HRC with adequate voltage rating. Reverse polarity is not possible, since the transistor and the rest of the circuit is behind a diode bridge (ultrafast 1.2kV diodes). The is also a massive inductor to slow down any sudden current inrushes.Sent from my HTC One M8s using Tapatalk.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: November 13, 2015, 11:29:12 pm
content: redesign it with a tube because i like designs that have as many weird technologies in them as possibleit needspeltier coolerslaserfluidicstubeshvmicrowavesdspexplosive bolts

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 13, 2015, 11:53:13 pm
content: Quote from: sarepairman2 on November 13, 2015, 11:29:12 pmTunnel diodesCryotronsParametronsCore memoryBackward wave oscillator