35 KV transistor ? - Page 1
Forum section: electronics / projects

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 05, 2014, 02:18:30 pm
content: Does such a thing exist?

author: penfold
author_rank: Frequent Contributor
timestamp: September 05, 2014, 02:48:32 pm
content: I'm sure that they have been made before, but they're certainly out of the bounds of commercial silicon. 35 kV is the sort of niche area that's mostly covered by vacuum tube technologies. Transistors can be rigged in series to provide that kind of voltage rating and are commonly used in multilevel converters in that fashion.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 07, 2014, 07:47:22 am
content: Quote from: penfold on September 05, 2014, 02:48:32 pmWhen you say rigged in series you mean something like this?To handle 35kV I'd need ~ 35 times 3 transistors? (!) Is that sane? Is there a better way?It seems there are engine ignition systems that use only one coil and no distributor/delco. How do they do to route the coil's 35kV secondary circuit to the proper spark plug?Thank you!

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2014, 08:00:08 am
content: Quote from: GeorgeOfTheJungle on September 05, 2014, 02:18:30 pmSounds like a 35kV transistor is a possible solution.But you'll get a better response stating what your problem is.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 07, 2014, 08:11:25 am
content: Quote from: tggzzz on September 07, 2014, 08:00:08 amThank you. The thing is single coil, multiple cylinder engine ignition systems: how do they do it (without a mechanical delco/distributor)?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 07, 2014, 08:20:54 am
content: No, transistors much over 10kV are impossible with known useful semiconductors*, and even those are tricky (not to mention unavailable).Perhaps diamond could best 20kV, but so far it seems it can't be doped usefully.I don't know if germanium was ever fabricated in higher voltages, but it would probably go up in the hundreds with modern processes (I expect the leakage current would be uselessly high, though).Silicon tops out just under 5kV. Diodes, IGBTs, SCRs and other big power devices are available up to 4400 or 4600V, IIRC.GaN isn't available in high voltages yet, which I'm not sure if it's because of processing or fabrication or what. It's primarily used in RF applications anyway, where voltages are always low.SiC is the current leader in breakdown voltage, I think. I've read papers about 10kV MOSFETs/IGBTs, though I haven't seen an actual production device for sale.Other materials (GaP, GaAs, InP, the various mixtures of related compounds; and more exotic ones like ZnO, etc.) should be similar, comparable to bandgap or something like that.Currently, the only known way to handle extremely high voltages in a single device is through a vacuum. Vacuum tubes for high voltage operation and power amplification have been built up to 30kV, although arguably particle accelerators count as high power controlling devices, extending well beyond the megavolts in equivalent voltage.Practical applications with high voltage requirements (e.g., HVDC power conversion) use large stacks of devices.Tim

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 07, 2014, 08:25:51 am
content: @admin: thanks for deleting the two (you know which) msgs. Yeah, it's much better so.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 07, 2014, 09:15:42 am
content: Quote from: T3sl4co1l on September 07, 2014, 08:20:54 amVery interesting, thanks a lot.So for this application, the ignition system of a say 8 cylinders engine, it seems to me it doesn't make much sense to use a single coil and tens of transistors per spark plug, isn't it?Perhaps the guy who told me that there are ignitions that use a single coil (and no mechanical distributor) is mistaken.A coil+primary driver transistor per cylinder seems to be the only sane way to do it... or not? What do you think?Thank you!

author: G7PSK
author_rank: Super Contributor
timestamp: September 07, 2014, 09:21:15 am
content: You can get silicon carbide mosfets rated to 1200 voltshttp://www.cree.com/Power/ProductsAnd IGBT to 6500 voltshttp://www.pwrx.com/summary/IGBT/IGBT.aspx?gclid=Cj0KEQjwhLCgBRCf0fPH043IlJwBEiQAf8P8U22UmKTqz-oWnEaxuJwEAk-wO6VTeh3znxCtXJ6kUfsaAsHN8P8HAQYou would not need so many of these in series.The usual thing with single coil no distributor engines is the wasted spark system where all the plugs get sparked at the same time but only one cylinder fires this has even been done on V8 engines by Buick.

author: penfold
author_rank: Frequent Contributor
timestamp: September 07, 2014, 09:28:29 am
content: There have been some solid state ignitions released, I had a Ford Escort Mk6 that had something that looked dubiously like a solid state distributor, it wasn't bulky enough to be a 4 way ignition coil (could have been though i suppose) but in that kind of case, if you were to ensure that one of the n transistors that you were using to commute the spark was always switched on, then none of the transistors ever sees 35 kV, they only ever see either nothing or the voltage dropped on the 'on' transistor, and therefore don't need a particularly high rating.I presume that this kind of method was a bit of a flash in the pan because I've not seen anything like it since, and most modern vehicles I have seen have been using a single ignition coil per spark plug, much easier to control and allows some redundancy

author: Richard Head
author_rank: Frequent Contributor
timestamp: September 07, 2014, 09:42:26 am
content: The single coil per cylinder with a driver transistor for each coil seems to be the way its going these days. This also eliminates the mechanical distributor which helps offset the additional cost of the individual coils. At present the switching transistor is normally located either in the ECU or in a separate module mounted on the firewall/engine. I expect this will change and it'll be located with the ignition coil module above each spark plug. This will dramatically reduce the EMI generated by the ignition system.

author: tautech
author_rank: Super Contributor
timestamp: September 07, 2014, 09:53:30 am
content: Quote from: Richard Head on September 07, 2014, 09:42:26 amThis was done in Jonsered chainsaws 30 Yrs ago.They moved away from it because of plug connection problems caused by the vibrating mass even though the coils where tiny, about 1/2 size of a matchbox.But in an auto motor, bolt them down.

author: Zero999
author_rank: Super Contributor
timestamp: September 07, 2014, 10:07:35 am
content: It's possible to use one coil per two cylinders but it means both spark plugs will need to be fired, even though only one cylinder is ignited. My two cylinder motorbike has one ignition coil and two cylinders.

author: SeanB
author_rank: Super Contributor
timestamp: September 07, 2014, 11:17:22 am
content: Coil per cylinder is about the best, or a single coil for two cylinders, which halves the number of coils but needs coil wiring, or a single large module with them all moulded in. There have been multicoil modules with 2 coil packs inside to fire a 4 cylinder engine, and these were both reliable and cheap, but the EMI was harder to tame, and you could not have a high power spark ( or multiple sparks per firing that a single coil pack can do) easily.Coil per plug can however be hard, just ask any VW owner of a 2001 or later VW with coil per cylinder engines and the coils that would almost always start to fail just at 40000km, just out of warranty. Bosch eventually had to recall the entire lot and replace them for no charge with an improved design, after there were enough documented failures. Thankfully my VW is using a single coil and distributor, and aside from cleaning every service it works fine.Removing the distributor allows a lot of reduction during assembly, as you lose an entire shaft, pulley, seals and a lot of extra precision boring of the castings. You also lose a lot of precision castings and machining in ther distributor as well, and make assembly easier as it all is then self aligned and needs no adjustment during first run, so makes the computer setup easier.

author: coppice
author_rank: Super Contributor
timestamp: September 07, 2014, 01:11:05 pm
content: Quote from: T3sl4co1l on September 07, 2014, 08:20:54 am30kV isn't very high for some types of vacuum tube. I used to work with 55kV TWTs, and that wasn't considered an exceptionally high voltage.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: September 07, 2014, 01:36:19 pm
content: How about going back to one of the original replies - what is it you are trying to do .Now your off to ignition systems , there is no transistors making KV for ignitions , its done with coils - primary 12v inducing current into a secondary coil making high voltage , solid state systems where running 50 - 70 KV using carbon impregnated synthetic conductors with thick silicone jackets .Like mentioned there would be transistors in the primary side for controlling , but none in the secondary HV side .So again to get direct replies to what your doing - tell us what you are doing ?

author: amyk
author_rank: Super Contributor
timestamp: September 07, 2014, 01:41:30 pm
content: Keep in mind that 35kV will also produce quite a bit of x-rays in vacuum tubes...

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: September 07, 2014, 01:49:20 pm
content: Quote from: G7PSK on September 07, 2014, 09:21:15 amBut, wow, haven't you seen the dimensions of these monsters?

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2014, 01:59:23 pm
content: Quote from: GeorgeOfTheJungle on September 07, 2014, 08:11:25 amThat is a statement of an application domain, not a statement of what you are trying to achieve, not what problem you are having, not what you have done to look for an answer.It might help if you readhttp://www.catb.org/esr/faqs/smart-questions.html#examples

author: DanielS
author_rank: Frequent Contributor
timestamp: September 07, 2014, 02:28:27 pm
content: Quote from: Hero999 on September 07, 2014, 10:07:35 amSome cars, like my 1.5L 2003 Hyundai Accent, use one coil pack per two cylinders too.The extra spark during the exhaust stroke is not necessarily a bad thing with modern long-life plugs: it helps burn off residue that might accumulate on them.

author: nuno
author_rank: Frequent Contributor
timestamp: September 07, 2014, 02:41:43 pm
content: Quote from: DanielS on September 07, 2014, 02:28:27 pmMy 1999 Ford Fiesta MK4 also has 1 coil per 2 cylinders. And the original 1996 MK1 version does it also (same engine).

author: N2IXK
author_rank: Frequent Contributor
timestamp: September 07, 2014, 02:54:40 pm
content: CPII/Eimac offers high voltage switching tubes up to 150 kV as "off the shelf" items:http://www.cpii.com/product.cfm/9/22/81At very high voltages, the tubes are usually operated in oil or SF6 gas to prevent external arcing across the surfaces of the envelope.