New "B-TRAN" Power Switch - Opinions? - Page 1
Forum section: electronics / projects

author: sandalcandal
author_rank: Unknown
timestamp: July 02, 2021, 05:18:17 am
content: Edit:Initial analysis and findings here.I've been made aware recently of this company:https://www.idealpower.com/technology/I wanted get info I might have missed, opinions and insights using publicly available information before I get locked down by NDAs.Their claim is a new form of bi-directional switch for power applications which has significant benefits in reducing losses.Key patent, 2013 filing, 2015 granted:https://patents.google.com/patent/US9209713B2/enPreview info sheet here:http://www.idealpower.com/wp-content/uploads/2021/05/BTRAN-Information-Sheet-V1.1.pdfThe switching energy loss looks less than stellar. 6mJ at 600V, 50A, 25°C. By comparisona similarly rated 3rd gen SiC MOSFET from Wolfspeedhas 0.71 mJ at 800V, 33A. Thoughan older 2nd gen SiChas 2.1mJ at 800V 40A. This is their first gen device so perhaps there are significant improvements to be made especially if they do their planned switch to SiC.Switching delays are also quite high.As with any completely new semiconductor device, I expect there to be initial reliability and manufacturing consistency issues. There will also be work figuring out nuances and working out how to get the best out of it.Initial public release of info on their new device is 2015https://ir.idealpower.com/press-releases/detail/550/ideal-power-releases-white-paper-exploring-the-benefits-ofhttps://solarbuildermag.com/news/power-semiconductor-switch-ideal-power/2015 white paper (image below):https://d1io3yog0oux5.cloudfront.net/idealpower/media/b875ed3ec8918b61ec0accd94b1f01fe.pdfFirst 3rd party validation of their device in 2016 apparentlyhttps://ir.idealpower.com/press-releases/detail/567/ideal-power-reports-semiconductor-fabricator-successfullyhttps://www.pntpower.com/ideal-power-report-successfully-tested-b-tran-transistor/Their first inventor in patent and CTO William C. Alexanderhttps://www.crunchbase.com/person/bill-alexanderhttps://ieeexplore.ieee.org/author/37662754200Their other inventor Richard A. Blanchardhttps://ieeexplore.ieee.org/author/37718316900

author: magic
author_rank: Super Contributor
timestamp: July 02, 2021, 07:05:16 am
content: The drawing you posted looks like some sort of symmetric, biderectional bipolar transistor.So, for example, why wouldn't it have slow turnoff due to charge storage like other BJT/IGBT?BTW, their IGBT and MOSFET drawings are utterly wrong, not enough layers

author: sandalcandal
author_rank: Unknown
timestamp: July 02, 2021, 07:38:35 am
content: Quote from: magic on July 02, 2021, 07:05:16 amYeah those drawing are completely whack.

author: magic
author_rank: Super Contributor
timestamp: July 02, 2021, 07:57:45 am
content: Ask them for an application note showing example circuits and how they benefit in terms of efficiency. They ought to have some idea about that or they wouldn't bother?The whitepaper is only a survey of the markets potentially interested in SMPS technology, nothing more than investor bait.

author: sandalcandal
author_rank: Unknown
timestamp: July 02, 2021, 08:17:09 am
content: Quote from: magic on July 02, 2021, 07:57:45 amThey also have a disproportionate amount of material on investor relations and their stock prices compared to technical/engineering material which seems worrying considering their lack of actual product in the market.I don't think they'd be smart approaching actual people for sales and samples if it was a scam however.I'll probably get that info (app notes and reference designs) later but it will be under NDA and might have document tracking so still trying to discuss what I can with publicly available info.Which whitepaper are you talking about? The new Jan 2021 on their website is a pretty useless look at applications but the 2015 one I attached has technical details along with switching transients. I still need to go over it in detail but my familiarity with semiconductor design (as opposed to application) is a bit lacking.

author: magic
author_rank: Super Contributor
timestamp: July 02, 2021, 09:56:39 am
content: Sorry, I downloaded the new paper from their website.The old one is here, btw, so no need to waste Dave's bandwidth with their junkhttps://d1io3yog0oux5.cloudfront.net/idealpower/media/b875ed3ec8918b61ec0accd94b1f01fe.pdfIt's definitely obfuscated or written for dummies or both. I now start to see that by "switch" they mean the gate-channel structure, so the P at the bottom of the MOSFET is the drain and the N on top is the body and the "switch" is the P channel induced within the N body which essentially connects the drain to the source. Similar story with the IGBT, which as drawn by them is of the "P channel IGBT" variety (behaving like a PMOS), extinct nowadays.In that light, their drawings kinda make senseTheir device doesn't appear to have integrated field effect "switches" on its surfaces, apparently both sides of the base are just brought out of the package for external drive.The trick appears to be that you can drive it like a BJT for very low Vce(sat), of course it takes some small auxiliary power supply to feed the base current into it. Then you short the bottom of the base to the emitter (with an external FET?) which shuts down minority carrier injection and you wait until the base is cleared of stored charge and behaves like an ordinary chunk of P- silicon (resistor). Without minority carriers current flows no more through the collector and you just turn off the top base drive and the device is off.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 02, 2021, 05:37:21 pm
content: GE (yes, satan's earthly representative) claimed to have invented a bididrectional Sic back in 2016http://www.semiconductor-today.com/news_items/2016/jun/rensselaer_290616.shtml

author: magic
author_rank: Super Contributor
timestamp: July 02, 2021, 09:10:15 pm
content: That's a biderectional IGBT and its forward voltage can never be lower than a diode drop, as in any ordinary IGBT.These guys would give you access to the internal N layer on both sides of the device, so you could pull current from it as from a normal PNP base and enjoy a high side switch with 200mV saturation voltage. (Note that the devices they showed so far are NPN, though).That being said, it is perhaps possible that some of the switches necessary for driving a BTRAN (see below) could be integrated on die as MOSFETs embedded in the structure, like in IGBT. But the driving process is still more complex than for IGBT and lowest forward voltage is only achievable with connection to that internal layer.

author: sandalcandal
author_rank: Unknown
timestamp: July 04, 2021, 06:14:54 pm
content: I had to go back and review some basic semiconductor theory here so someone please correct me if I make mistakes.Iffy Whitepaper Explanations/DiagramsI found the explanations of conventional devices and Ideal Power's B-TRAN given in their 2015 white paper strange and confusing. As magic mentioned, the diagrams don't really show a complete structure instead they show a sort of truncated representation of the main conduction path and the very important control structures have been replaced by abstracted switches. The diagrams and explanations do very little in the way of illustrating the drift regions and charge carrier flows which are typically important to understanding device function. This unconventional explanation I guess obfuscates a full understanding of how their device actually functions but still gives them some ability to explain the differences in their device compared to a conventional MOSFET or IGBT.Attempted Reading of the Patent(s)Fortunatelythe key patent is publicand gives much better details without obfuscation but some details such as semiconductor manufacturing optimisations and embodiments go well above my head. I'm also going to just assume and consider an NPN device to make this easier for now.Principle of Operation with Equivalent CircuitAbove is a an equivalent circuit schematic from the patent with some annotations added by me to make the example operation a bit clearer, the patent itself has a series of schematics illustrating operation but hopefully one drawing is enough to give a basic idea with my simplified explanation. The device itself is in the dotted box and operation of the device is achieved by operating the external switches with bias voltages. A positive bias from T1 to T2 is applied in this example.1. OffIn the "off" blocking state, the low-side base (B2) and low-side terminal "emitter" (T2) are shorted by the switch 314B. This ensures no current flows in the lower PN junction (diode) 312B i.e. no minority carriers are available. Voltage is blocked by the upper PN junction 312A.2. Diode-OnThe first phase of turn-on described is as the "diode-on" where the high-side terminal "collector" (T1) and high-side base (B1) are shorted by the switch 314A. This shorts T1 into the middle "base" node/resistor/region and forward biases the lower PN junction 312B which starts injecting the the base/drift region with minority carriers.3. Transistor-OnThe second phase of turn-on and the primary operational state for conduction is described as the "transistor-on". The high-side PN base-"collector" junction 312A is forward biased by closing the switch 316A and simultaneously opening the switch 314A. This further injects minority carriers into the base/drift region thus lowering further lowering conduction loss. This is somewhat similar to BJT saturation (I think?). Note: this current is opposite to the main conducted current, thus will reduce the "collector" current.4. Pre-Turn-OffBefore turning off, the device accelerates the actual turn-off be doing a what is described as the "pre-turn-off". The high-side base-"collector" bias is removed by opening the switch 316A and closing both B-T shorting switches 314A and 314B thereby bypassing both junctions and removing charge carriers.1. OffFinally to return to the complete "off" blocking state, the high-side B1-T1 switch 314A is opened and the voltage is blocked by the upper PN junction 312A.The complicated control scheme reminds of some weird reverse driving techniques I vaguely recall hearing about being done to improve BJT speed.Basic doping structureAbove is a drawing from the key patent showing an example doping structure for the B-TRAN. It looks to me like a NPN BJT transistor but with an unconventional symmetrical doping structure and a very large, stretched out drift region; I guess that's to be expected given the full descriptive name of the device used in marketing material and the patents "Bi-Directional Bi-Polar Junction TRANsistor". From this you might guess it behaves like a BJT with poor gain and poor high frequency performance but high voltage handling and the preview datasheet/information sheet seems to reflect that.Control TimingThe timing of the operation phases also needs to be carefully controlled to achieve optimisation. They have patents on drivinghere (US9742395B2)andhere (US10211283B2). I would need to read and analyse more but I would think optimal drive currents and timings will vary depending on current levels (carrier densities) within the device which will complicate control/drive circuitry that much more.Parasitic Turn-OnThere is also additional externals components to prevent parasitic turn-on/breakdown due to AC transients consisting of a Schottky diode in series with a JFET or resistor across each base-terminal pair. The system is described bya patent here (US10497699B2).PROSLowest On-State Loss at High CurrentThe funky structure and driving method means that once the transistor-on phase is achieved the device has very low losses at high currents. Lower loss than MOSFETs or IGBTs. Similar to a BJT with very low Vce(sat) but the drive current subtracts from the "collector" current instead of adding to the emitter current like a more conventionally driven BJT.High Voltage*The device has quite high voltage rating, advertised as on par with IGBTs. This seems plausible due to the very large depletion layer/drift region in the construction/operation of the device. *If the given rating is actually achieved with reliability and ample margin remains to be proven at this stage. The device may require other aspects of performance to be reduced to achieve the advertised voltage rating with reliability but at the same time it may not or even have improvements that allow performance improvement without sacrificing blocking voltage reliability...who knows at this point.A minor PRO, it is not really relevant with modern IGBTs but the lack of 4-layer structuring means latch up is not possible.CONSExternal SwitchesAFAIK the switches and driving circuitry are all external to the chip/device/package. In order to perform the diode-on phase, another external switch between the base and terminal (emitter/collector) pins is required which can withstand the full switched voltage AND the initial turn-on current. Similarly for the pre-off phase, the switch must also take over the complete switch current and then turn off that current flow. This is only for a short transient so a high pulsed power switch could be used butthe switching losses are essentially being offloaded onto the control switches. I wonderis the loss from the control switches accounted for in their advertised switching loss energy figures?High Drive CurrentThe device has a very low current gain. From the information sheet.hFE(sat) = 3(typical). Looking at output characteristic curves, to achieved the rated 50A at T_c = 25°C, a base current of ~12A is required. This drive current is only across ~0.8V compared to the the >600V switched voltage so the switched power is still much larger than the drive power but there is still considerable on-state driver loss. As mentioned before, I'm guessing this low gain is likely due to the very large base/drift region which current is to be amplified in. Also a reminder this drive current passes through the device in the opposite direction to the main conducted current so results in lower net current on the driven "collector" terminal.Likely Higher Overall CostsIt is implicit for a new technology with small production volume from a small supplier that cost will be relatively high unless there are major innovations allowing cost reduction. However, in this case there are increased costs of the control switches and the floating drive circuitry and floating power supplies required for the control scheme employed by this device. I believe a system implementation using B-TRAN will have a significantly higher total system cost compared to an equivalent IGBT implementation.UNKNOWN/UNDECIDEDBidirectional SwitchingI'm not really sure what application benefits from the symmetry of this device. The only thing that comes to mind is applications when switches are used as solid state blocking elements, e.g. SSR, a battery protector or power supply cut-off; one of the demonstration applications shown is a DC circuit breaker. The lack of integral diode means that an external/co-packaged diode must be used for inductive switching but that being said, you typically do not want to use the body diode of an IGBT or MOSFET for high efficiency freewheeling anyway. I would assume that better performance could be achieved using a similar driving regime but limiting to unidirectional application and optimising an asymmetric structure. I can't really think of any power conversion topologies that benefit from a bidirectional switch?Device Switching PerformanceDoing a limited comparison to~6 year old IGBT with equal voltage rating but double the current handling and significantly higher power ratingusing only datasheet values, it can be seen that switching performance at 25°C is apparently worse. Switching speed and switching energy losses are all worse. That being said, the B-TRAN is still a pre-release "zeroth" gen device so significant improvements could be made?Double Sided Doping ProcessThe double sided structure conceived for the B-TRAN seems to have required the development of some doubled sided doping processes. I feel like this should result in higher production costs and packaging complexity but could maybe result in better wafer utilisation?Initial Opinions (Conclusion)The B-TRAN is a very unconventional BJT designed and optimised to operate with a very unconventional and complex drive system which aims to enable BJT-like loss at higher blocking voltages whilst attempting to minimise sacrifices in switching performance. The low BJT-like loss and blocking voltage seems to have been achieved but I'm not convinced the overall switching performance is preferable to that of an IGBT. The somewhat complicated switching sequence effectively passes the switching loss plus extra junction recovery energy onto external "control" switches, the B-TRAN itself can be considered a low loss, on-state bypass for an alternative set of switches in this regard.Definitely not a device suited to what I do/need. I need high levels of power but I also need high switching frequency in order to reduce size, weight and cost (of passives). The very high inherit switching losses of the device plus the switching losses in the control switches makes it very unsuitable for even "medium" frequency (>10kHz).The only niche the B-TRAN seems to fit in is between IGBTs and electromechanical relays. High current handling is better than IGBTs but switching performance looks to be equal if not worse than IGBTs particularly with the much more complex drive requirements (with high driver loss and driver cost) in order to approach IGBTs switching performance. I imagine lower losses (per $) can still be achieved using electromechanical switches but electromechanical relays suffer limited cycle count lifetime unlike the B-TRAN. I would NOT say the B-TRAN is 100% more reliable or longer life than an electromechanical switch however due to the complex drive circuitry and potential for failures there.I think the B-TRAN is ideally suited to applications where low frequency switching or constant cycling of very high current, power is required.From what I currently have garnered, it is not (yet) competitive with other modern semiconductor switches used for power conversion.

author: magic
author_rank: Super Contributor
timestamp: July 04, 2021, 07:47:44 pm
content: That figure 3A is confusing as hell.Nice writeup and it mostly agrees with my impression.Quote from: sandalcandal on July 04, 2021, 06:14:54 pmI missed the part about shorting out the lower junction. I suppose some voltage would still be blocked without it (by the upper junction), but the short prevents β-multiplication of leakage current. Like Vceo vs Vces in traditional BJT.Quote from: sandalcandal on July 04, 2021, 06:14:54 pmThis is equivalent to diode-strapping traditional BJT. They probably do it to avoid exposing the base drive auxiliary PSU to full rail voltage during turn-on. Trying to avoid the diode phase would be all sorts of fun, methinks.Quote from: sandalcandal on July 04, 2021, 06:14:54 pmI think saturation is prevented by carefully choosing base drive PSU voltage. For instance, if it's zero, then you have the diode behavior as above. If it's 300mV, then collector can go 300mV less than Vbe and only 1/β of load current experiences full Vbe voltage drop (and the energy delta is provided by the drive PSU). But you can't push too far because at some point the upper junction starts to conduct meaningful current and in extreme case it could outright short out the drive PSU.And yes, I botched my yesterday description of the turn-off process a little

author: sandalcandal
author_rank: Unknown
timestamp: July 05, 2021, 01:40:26 pm
content: Thanks for having a read and the comments, magic.Quote from: magic on July 04, 2021, 07:47:44 pmTrying to deliver 12A of controlled current at 0.3V to 0.8V withminimum additional lossesin the drive circuitry sounds like it will be an additional non-trivial complexity in the driver circuitry design.

author: heuristocrat
author_rank: Newbie
timestamp: June 22, 2023, 08:05:41 pm
content: I went through this thread from 2021, and I am curious if anyone has kept track of it or taken a fresh look? Since then, it seems that the company has made some progress and is moving into manufacturing at one or two approved fabs.It does sound like some of the benefits they tout don't consider the related support and driver circuitry. Maybe this device could have an advantage for some applications, but there are so many monster suppliers in this category; why would we need to work with a small company like this?