Silicon Carbide  - Page 1
Forum section: electronics / general

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 12, 2021, 02:37:51 pm
content: Just out of curiosity;Have you actually employed SiC devices in a product which is currently produced and sold.In other words, not prototypes or single use lab apparatus?Even though SiC holds lots of performance advantages, I’ve not seen mainstream implementation.... or am I wrong?

author: Siwastaja
author_rank: Super Contributor
timestamp: February 12, 2021, 03:44:40 pm
content: I'm quite sure they are in all modern high-power boost PFC stages.

author: TimNJ
author_rank: Super Contributor
timestamp: February 12, 2021, 05:01:32 pm
content: Mid to high-end power (300 - 600W) supplies with CCM PFC stages have been using them for at least ~3 years, I think. Personally, using SiC for a ~100W CCM PFC stage. (Ordinarily this would be TM/CrM, but need exceptionally low input current distortion.)The power savings is huge!! ST, Toshiba, Cree all have parts I believe.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 12, 2021, 05:26:13 pm
content: You can think about it this way: SiC enables much better utilization of the (expensive) inductor, and/or lower inductor losses, because you can now run in CCM. Before SiC, boost PFCs were often deliberately designed for boundary conduction mode only because the reverse recovery of standard Si diode sucked beyond belief.

author: JohnG
author_rank: Frequent Contributor
timestamp: February 12, 2021, 06:21:29 pm
content: Rumor has it that the Tesla Model 3 uses ST SiC MOSFETs.Also, SiC MOSFETs enable use of synchronous rectification in a boost PFC, because the reverse recovery is so much less than any Si MOSFET body diodes. If it is still too much, you can use an antiparallel SiC Schottky diode, though the extra capacitance might make it a wash. This also works better than with Si because the SiC MOSFET body diode has about 4V drop, and the SiC Schottky only 2V, so nearly all the current goes into the Schottky. For some reason, this is part of so-called "bridgeless PFC", which is not bridgeless, it just replaces the usual AC bridge rectifier with some active half-bridges.Or you can use 600V GaN, which has no reverse recovery.Cheers,John

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 12, 2021, 08:04:12 pm
content: Siwastaja;I believe your reply answers my question, about the reason for SiC perhaps not being used everywhere, like a mobile charger or other lower power stuff.The cost of the magnetic devices is not such as to justify the more expensive SiC devices.However as power increases and the cost of the magnetic components increasing to eyebrow-rising levels, the more expensive SiC can be easily justified.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 13, 2021, 09:44:51 am
content: Power dissipation requires heatsinking which also has a cost.It's a longer trend that throwing more silicon at the problem may be cheaper than throwing more heatsinking at the problem. Classic example being paralleling more power transistors to parallel the RthJ-C values to allow for a smaller heatsink for the same Tj!If you look at the total cost of ownership, then it's even more pronounced as it makes sense to save energy. Manufacturers don't think about this much beyond what the legislators require regarding efficiency.It completely depends on the topology and specs of the product, in some cases SiC diode makes things worse (like an extra low voltage converter; SiC has higher Vf; use classic schottky instead!), in some cases it would not make much difference (a converter running in BCM anyway), in some cases the difference is massive (like a high-voltage boost running in CCM, the reverse recovery losses of the best classical fast/soft recovery silicond diodes can be tens of watts in a few hundred watt converter!)SiC diodes were expensive in 2010, they are not that expensive anymore, if the design really needs it, it will be a no-brainer.SiC MOSFETs seems to be a more recent thing, I haven't looked at them.

author: jbb
author_rank: Super Contributor
timestamp: February 16, 2021, 11:41:26 pm
content: SiC diodes are used in PFC rectifiers.SiC MOSFETs are used in PV inverters (from SMA and others) on the market.I expect there’s quite a bit in power automotive, aerospace and railway.In general, a wide band gap device like SiC (or Gallium Nitride) might be a little more expensive than a Si part. But the SiC parts have better properties, so maybe you can increase the switching frequency and shrink your inductors, transformers and capacitors. That could well save you money on purchasing, assembly and shipping.

author: Circlotron
author_rank: Super Contributor
timestamp: February 17, 2021, 01:02:35 am
content: I worked in an SMPS design lab for 10 years till 2005 and at that time SiC Schottkys were becoming available but not widely used. We were on the cusp of using one in one of our PSUs. I spent a LOT of time messing with lossless resonant snubbers to manage the reverse recovery of normal soft recovery diodes in PSUs up to 3kW size with 450VDC buss. One of the issues with PFC stages was controlling mosfet drain voltage overshoot at turnoff because you would have various inductors and diodes and caps around and in series with the main diode, and of course the length of the associated pcb tracks with their inductance. With a SiC Schottky though you could throw away all that extra paraphernalia and make a simple short and direct connection from the mosfet drain through the diode to the big output caps. Overshoot problem soooo much better. I seem to remember that EMC was somewhat easier too. At the time I remember thinking it was like when 3-phase motor drives moved away from force commutated SCRs with all their additional inductors and capacitors and diodes and instead used IGBTs. Way simpler. As has been stated, if your boost inductor is in CCM then nowadays it’s a no brainer. It would be like using a bipolar power transistor for an SMPS when mosfets are readily available.

author: JohnG
author_rank: Frequent Contributor
timestamp: February 17, 2021, 03:26:37 pm
content: First, the disclaimer: I work for a wide bandgap power semiconductor company. Before that, I worked at another company where I spent a lot of time investigating wide bandgap power semiconductors. It is true that I am biased, but that bias has about 15 years of experience behind it, both good and bad (including the wake up in the middle of the night thinking "Oh $h1t, what the hell did I just do" bad).I think you will see a lot more wide bandgap power semiconductors, and power silicon will be gradually displaced, or maybe not so gradually in some cases. They come with some challenges, which mainly are due to smaller die size and faster switching. These are often brought up as boogie-men, in particular PCB layout and/or power bus design, thermal management and EMI. Indeed, these aspects can be more challenging, but successful products using GaN and SiC are on the market, which means that the challenges can be met and the system performance/cost ratio favors the use of wide bandgap semiconductors in these products.They have also reached a maturity level that makes enough people comfortable. The early days were pretty rough. Threshold drift and bipolar degradation in SiC, dynamic R_ON in GaN, new device structures and attendant process development, material quality, etc. For example, one company's early SiC Schotty diode had field failures that scared a lot of people and set things back several years. Now, though, many of these parts can take more abuse than the Si parts they replace, and there is literally years of reliability data available from more reputable companies.Another issue is cost, as most (but not all) wide bandgap semiconductors cost more. Even if the system cost is less overall, this is really difficult to show without building something. Making prototypes to see if something is commercially viable is a lot harder than building a prototype in grad school. It has to work AND be cost effective. Some companies have done the work, and other companies can do teardowns and cost analysis of the products, saving themselves a lot of work and time (though not all).Just my $0.02,JohnCheers,John