What makes an automotive mosfet "automotive"? - Page 1
Forum section: electronics / beginners

author: Molenaar
author_rank: Regular Contributor
timestamp: July 26, 2015, 12:13:58 am
content: Some mosfet are classified as automotive, but what makes them that?Say I want to switch an ignition coil using a microcontroller, would any 500+ V fet do, if things like a small RDSon are taken care of? Or would an "automotive" certified mosfet be neccessary?I understand that automotive microcontrollers are supposed to be more rugged, but a normal 500+ V mosfet should be rugged enough anyway, if it is in a mechanically strong package.

author: Psi
author_rank: Super Contributor
timestamp: July 26, 2015, 12:21:10 am
content: Usually an automotive part will have a wider operating temperature range, maybe -40 to +125C instead of 0 to 85C.They can also be tested more rigorously by the manufacture to make sure they conform exactly to the specs. (a non-automotive part might only have one part per batch tested fully and not every part)Automotive parts sometimes have transient protection built-in, so they can withstand short spikes well above their rated voltage without damage.They almost always come off exactly the same production line as the non-automotive version.It really depends on your country but most places don't have any legal requirement for all automotive electronics to use automotive rated components.However, to list your product as complying with automotive qualification xyz on the product packaging you need to met the requirements of that standard.To switch a 12V load on/off in a car you dont need a 500V mosfet. Anything above maybe 60V would be ok because there should be other protection that will clamp any spikes to ~40V (like a 26V TVS diode which will clamp spikes to 39V).However things do get a bit more complicated with ignition coils because the whole purpose is to generate high voltage ringing on the primary side.Perhaps in that application a 500V mosfet would be a good idea, if you can handle the higher Rdson value.But you still have to clamp high voltage spikes in your device from escaping onto the cars 12V power rail, even if internally there's 100V ringing going on inside your device.

author: c4757p
author_rank: Super Contributor
timestamp: July 26, 2015, 12:40:03 am
content: QuoteThe ability to move under its own power, obviously. Lighter ones will do this if a sufficiently high power is dissipated in them in a short period of time.

author: langwadt
author_rank: Super Contributor
timestamp: July 26, 2015, 01:20:38 am
content: Quote from: Molenaar on July 26, 2015, 12:13:58 amfor an ignition coil you want to use something with a voltage clamp, something like this:http://www.onsemi.com/pub_link/Collateral/NGP8203N-D.PDFthe clamp protects the ignition coil by dissipating the energy in case the ignition cable is loose or something like that

author: Psi
author_rank: Super Contributor
timestamp: July 26, 2015, 01:33:18 am
content: yes a mosfet/IGBT with built in clamping protection would be a good idea

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 26, 2015, 03:30:43 am
content: The ones that specifically say "automotive", and are aimed at ignition and stuff, are usually some kind of pre-cooked transistor with the gate resistor (relatively large, to limit risetime) and protection zeners included. As such, they're no good at all for general switching purposes, which you have to look out for.If that's precisely what you're doing -- ignition -- they're perfect for the job: just slow enough to save on EMI without sacrificing voltage or whatever. That does assume you use a conventional iron cored ignition coil, that doesn't need a fast risetime.Tim

author: Neverther
author_rank: Regular Contributor
timestamp: July 26, 2015, 05:29:18 am
content: Like in post above, there are designated components for driving ignition coils.For example some megasquirt versions use VB921ZVFI, go look up the datasheet to see all the features it has built in vs normal mosfets.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: July 26, 2015, 07:56:09 am
content: I think the fact that component is used in ignition system does not by itself makes it "automotive". "automotive" tag is more like to ensure that it meets liability requirements. Another one would be "medical". Since ignition system may not be part of safety systems it does not have to be "automotive" - paradoxical huh?There is one more theory that I myself was always curious about: I think it also has something to do with "life cycle" - there should be guarantee that components will be available as longs as cars it is part of are in active use. Is it this true or just some kind of MYTH?Wikipedia article on automotive electronics explains it pretty goodhttps://en.wikipedia.org/wiki/Automotive_electronics

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 26, 2015, 09:14:33 am
content: Automotive components in most cases are ordinary industrial series products,and NOT specifically designed for automotive.(You have to account for the price pressure in automotive also!)The suppliers have to prove that these components for automotive use have to fulfill the tests according the AEC-Q standards, for discrete semiconductors, that is AEC-Q101 (Rev -D). You may find them here:http://www.aecouncil.com/AECDocuments.htmlFor MOS-FETs, you may find additional requirements in the AEC-Q101-4 "Miscellaneous Test Methods"General specification requirements are, for example, full operation temperature range of -40..+85°C for Interior, -40..+125°C for Power Train , and up to 175°C in special application (mostly bare die).Vibration, temperature shock, solderability, etc. are contained within the AEC-Q documents.Additionally, the suppliers have to warrant these requirements and are fully held liable for damages.. which could easily ruin a supplier.That's the really severe aspect of "automotive components.They can either fulfill that by setting up an automotive grade quality management system (which is also strictly required for any automotive supplier), or additionally by designing more robust parts, using additional development methods.Also, they might use more reliable / better manufacturing sites for automotive parts.For example, automotive resonators or X-TALs are mostly manufactured in Japan, instead of China.Frank

author: HighVoltage
author_rank: Super Contributor
timestamp: July 26, 2015, 09:35:34 am
content: One of my OEM clients was using an ON semiconductor automotive ignition IGBT and it was guaranteed to do the job perfectly. It turned out the failure rate was over 1% after one year and it became a nightmare. The IGBT manufacturer was switched to Fairchild. Failure rates dropped immediately and right now there are no known failures in this production line with the automotive IGBT.In this particular case, the peak current was 8A and the clamping voltage reached 400 Volts and the stored energy was around 60 mJNothing very special and still dramatic failures.So, sometimes it is labeled "automotive" it is fulfilling all requirements on the datatsheet and still fails the harsh power train requirements under the hood.

author: Molenaar
author_rank: Regular Contributor
timestamp: July 26, 2015, 11:24:43 am
content: I forgot to include this in the OP, but this is meant as a one-off project to improve the ignition of my old Mercedes W108 250S by using a wasted spark design. Six cylinders, so three coils driven by a microcontroller (TI TMS570LS1224). I'm more of an (embedded) software guy, so please forgive me any rookie hardware mistakes. However, I'm quite sure it should be easy to improve on the cheap/crappy velleman kit which I currently use, that, in turn, has beaten the original point-driven ignitionQuote from: Psi on July 26, 2015, 12:21:10 amI am aware of the extended temperature range and was planning to use a HV diode to block spikes from the coil propagating back, as well as a flyback diode to dissipate them.Regarding the RDSon, the STP45N65M5 has a RDSon of 0.078 ? (max), which should be OK if combined with coils in the 1+ ? range, although I might go for IGBT's after all, since they're much cheaper and the diode style voltage drop becomes increasingly attractive with lower coil resistance, which might ease coil selection and leave more tuning options (air cores?) open.Quote from: langwadt on July 26, 2015, 01:20:38 amI'm not sure I understand the implications of a loose ignition cable, except of course bad engine control. I would assume the end of the cable would just spark over and that's that, but if that's not the case, power might be transformed back to the LV side, where it would be dissipated by the flyback diode. Voltage/current sensing would enable detection of this, so the microcontroller can cut the power and switch off the two affected cylinders. Am I overlooking something?Quote from: T3sl4co1l on July 26, 2015, 03:30:43 amI'm a bit worried about the relatively slow turn off of IGBT's vs mosfets (SL9V3040: 2.8 us (typ) vs STB45N65M5: 9.3 ns (type)). I try to be as agnostic to the ignition coil as possible; wouldn't this impede the creation of powerful sparks if I would go the air coil route?Quote from: Dr. Frank on July 26, 2015, 09:14:33 amSince this would be for personal use anyway, I don't think this would be that big of an issue for me.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 26, 2015, 11:47:46 am
content: Quote from: Molenaar on July 26, 2015, 11:24:43 amYou will not notice a difference between a fast MOSFET and an ignition IGBT. The slowest part in your system will always be the reaction of the ignition coil itself and is more depending on your selection of coil. If you want really good performance gain on your old W108, install 6 coils and use those that have already the complete circuit inside the coils, including all the protection circuit and a heat sink. And, if you sill want to send only 3 signals out from your microcontroller, you hook up two coil input signals in parallel. Do not use waste spark, if you are looking for some gain in spark performance.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2015, 11:59:59 am
content: If you are still using the stock Bosch plugs ( forget the platinum ones, they are useless) buy Lodge gold or silver, and get the highest power ( lowest resistance and inductance) coil that will fit in the regular ignition system, probably a ballasted one. That, along with low resistance inductive leads, will increase spark energy by a whole lot, at the expense of replacing plugs at every service as there will be no electrode left, and having to change rotor for the same reason. You will be buying rotor caps as well every so often as the electrodes wear back into the housing.

author: Molenaar
author_rank: Regular Contributor
timestamp: July 26, 2015, 12:18:58 pm
content: Quote from: HighVoltage on July 26, 2015, 11:47:46 amThanks for the suggestion, I might indeed go with plug top coils. Since most coils are meant for specific car models, could you recommend one?This microcontroller is very much overkill and has more than enough pins available to control all coils separately, so no problem there.Quote from: SeanB on July 26, 2015, 11:59:59 amMy goal is to improve both spark timing and strength, so I would like to replace the mechanical distributor.Aside from performance goals, it is also for fun and to learn

author: poorchava
author_rank: Super Contributor
timestamp: July 26, 2015, 12:47:57 pm
content: Automotive mosfets are qualified for high temperature operation. The they are also very often rated for withstanding certain fault conditions like avalanche breakdown energy, which may happen for example during load dump event. Also the package must be tested for resistance to delamination, moisture ingress, temperature shocks and such.Sent from my HTC One M8s using Tapatalk

author: HighVoltage
author_rank: Super Contributor
timestamp: July 26, 2015, 01:18:48 pm
content: Quote from: Molenaar on July 26, 2015, 12:18:58 pmI would not use a Plug Top Coil for this engine. That would be very weird - kind off. If I remember right, this engine had the spark plugs in an angle and there is not much space for adding top plug coils. Although there are plenty of coils available, one comes to mind that will fit your application the best. It is an OEM coil for a high power outboard engine but it works extremely well. Without promoting myself, I have worked with the OEM coil manufacturer on this coil design and construction a long long time ago. It is so stable, it is being used in the automotive OEM field now, even for 10l Truck engines.There are some significant differences to other coils:1. You have a seperate secondary ground connection to be connected to engine ground.2. The input is a differential input with separate Engine Control Unit ground, which you can connect to your micro controller ground without any disturbances3. It has a 3rd ground connection just for powering the circuit.Probably best to buy here:http://www.aemelectronics.com/?q=products/ignition-components/high-performance-coils/high-output-igbt-inductive-smart-coilMake sure to use some inductive spark plug wires with low resistance, as SeanB has pointed out and if you can, use pure silver conductor spark plugs.You will not recognize your old engine after this modification.I used this coil with another large OEM truck manufacturer in Europe for a lean burn engine with a Lambda of 1.5No other "normal" ignition was capable of igniting this engine under full load. And this engine is in production now with this coil, just slightly modified.

author: langwadt
author_rank: Super Contributor
timestamp: July 26, 2015, 03:17:05 pm
content: Quote from: Molenaar on July 26, 2015, 11:24:43 amyou can't have a flyback diode then it won't work, the turns ratio on an ignition coil is only ~1:100 so you have to let the primary flybackto a few hundred volts to get the ~20kV on the secondary.The point of the clamp is that if there is a loose cable the secondary voltage might rise to the point of sparking inside the coil

author: Molenaar
author_rank: Regular Contributor
timestamp: July 27, 2015, 08:16:58 pm
content: Quote from: HighVoltage on July 26, 2015, 01:18:48 pmLooks promising, although I was not anticipating spending ~450 euro's on coils alone, without even taking into account the MCU board, although it would be a bit less with the passive coils.Could you suggest a decent but maybe not high performance part for comparison?To put it into perspective, the previous owner drove it without the vacuum system properly working, so especially idle it runs relatively rough, so I think high performance coils might be a step too far given the cars current state.Quote from: langwadt on July 26, 2015, 03:17:05 pmI meant a flyback diode at, let's say, 100 V below the breakdown of the mosfet/IGBT, but maybe it's overkill to use a dedicated diode for that. The body diode might suffice.

author: McBryce
author_rank: Super Contributor
timestamp: July 27, 2015, 08:33:01 pm
content: Quote from: Alexei.Polkhanov on July 26, 2015, 07:56:09 amIt's not a myth. Automotive parts have to be available for 10 years after the cars EOL. But this is only applied on an OEM Part No. level, so only the Tier one supplier is obligied to guarantee this. If the module is small and cheap, the supplier sometimes just guesses how many are going to go wrong from the previous 16 years of replacements data. Then they pre-produce the stock to cover the time so that the machines can be packed away. The machines and all drawings need to be preserved for that time too though.On the original question. In some cases automotive parts can also have physical differences, especially the solder area (thicker pins, alternative package). The vibration tests are more extreme for these.McBryce.

author: langwadt
author_rank: Super Contributor
timestamp: July 27, 2015, 08:59:33 pm
content: Quote from: Molenaar on July 27, 2015, 08:16:58 pmThen you'll just have to find room for another diode big enough to handle the energy, it makes more sense to use either a mosfet/igbt that is avalanche rated or clampedThe simplest option is to use one of the numerous coil packs or coil on plug that include the driver and just need 5V gate drive

author: Molenaar
author_rank: Regular Contributor
timestamp: July 28, 2015, 10:38:46 am
content: Quote from: langwadt on July 27, 2015, 08:59:33 pmThe simplest option is to buy a modern car instead of an oldtimer. But where's the fun in that?I think I'll opt for designing the driver myself while using air core coils, unless someone can convince me it would really be much more efficient to just buy the complete package.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 28, 2015, 11:11:49 am
content: There is no problem in designing your own circuits, especially when you use the Fairchild ignition IGBT.If you go that route, use the Bosch ignition coil that was in the old Mercedes 190E (Engine M102 / M103) because that coil has the most energy of all the older type coils. This Bosch development was years ahead of the competition in the early 80s and tons of research papers have been published on this coil. It is a closed core coil with an air gap of course and really good built quality. The good thing is, you can use original Mercedes spark plug wire connectors and it will look kind of fitting to your car.The other route...If you are looking for a very low cost coil with internal driver and control circuit, take a look at the Golf 4 coil, the last VW with a distributor type ignition.This coil has an aluminum foot/heatsink and delivers also good energy. It is either made new today by TEMEC or BERU and should be easily available in Germany.

author: Molenaar
author_rank: Regular Contributor
timestamp: February 19, 2016, 10:41:47 am
content: Just a follow up post: so I decided to go ahead and design something using the suggestions from this topic (seehttps://www.eevblog.com/forum/projects/ecu-for-a-mercedes-oldtimer-with-ionizing-current-sensing/), such as the Fairchild IGBT and the AEM "dumb" coil. Thanks for all the feedback!