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Last week, I compared Tesla design to Apple. Since then, it has become widely known that Elon Musk tried to sell Tesla to Apple in 2013. This has created considerable interest in Apple's autonomous vehicle project and Apple's progress with lithium batteries. However, it has not created considerable interest in Jony Ive's possible work for Ferrari nor in the progress of power transistors. I wrote about gallium LEDs and transistors in Dec 2017 and, specifically, GaNFET (Gallium Nitride Field Effect Transistor). I thought that it would be a good idea to check progress. Well, holy cr*p.
On Mon 9 Nov 2020, a Texas Instruments press release announced power transistors which can switch 4kW (more than 600V, more than 6A) at 2.2MHz and, due to the 30mΩ resistance, do this with 99% efficiency. Indeed, cables may warm more than the 12mm×12mm transistors which require, at most, 40W heatsink. My calculations may be wrong but a homebrew, all wheel drive, six wheel vehicle, with 16 phase electric motors and these 4kW GaNFETs, can do a standing start quarter mile (400m) in less than 10 seconds. By 1980s standards, this is supercar performance. And from 2021 Q1, it is now possible to make this at home or a local makerspace.
The price for these transistors is US$8.34 each for the lowest grade and US$14.68 each for the highest grade if purchased in quantities of 1000 or more. If you don't have US$8340 or so, there is an evaluation module for US$199.
I'm not sure of Moore's law applies to individual transistors but this is now the upper bound for 4kW power transistors. Unfortunately, many of the problems which I previously identified remain. Gate leakage is mitigated with an integrated driver, although (my estimate) leak of 30-50mW is probably not a huge concern when switching 4kW. The major problem is that the technology is in transition and therefore it still uses silicon as a substrate. The mismatched atom size is a hinderance to the efficiency of gallium nitride transistors and LEDs. Expect at least double improvement when this moves to a gallium nitride substrate. Therefore, expect 10kW switching at 5MHz or more.
Switching this amount of energy under software control is extremely dangerous and may cause equipment to not just smoke but spontaneously explode. I strongly recommend safeguards, such as hardware interlocks, watchdog timeouts, disallowing field firmware upgrades and control protocols which fail in a safe manner.
As I've previously noted, in less demanding applications, such as quadcopters, it is desirable to remove a heatsink entirely. This leads to a moderate step change because a subset of designs no longer expend energy to keep a heatsink aloft. This provides an otherwise unmodified design with more range and more flight time. The advantage is also compounding if a design is made smaller.
Anyhow, autonomous supercars, quadcopters and spontaneous explosions. What could possibly go wrong?
(Score: 4, Interesting) by Rich on Tuesday December 29 2020, @05:44PM
Had a look at the TI datasheet. I found the most impressive thing was the packaging: it's a diddly 12x12mm^2 QFN. Other than that, the integrated drive and overcurrent support is a very welcome feature for spec'ing them, if you read all the discussions on how to properly do gate drives for high power mosfets. It also looks (on a first glance) like it can generate its own high side control power, which again makes things more clean and easy.
I hadn't looked much past the IRF3205 so far. Checking Mouser, the older GaN FET competition seems to be from Transphorm and Nexperia, both have a classic gate drive, higher internal Rdson resistance (72 and 50 mOhm vs 30 for the TI), and cost about half (TI $14 at 1000, Nexperia $7). There's a new Transphorm TP65H035G4WS in TO247 with 650V and continuous drain at 25C of 46.5A (30kW...), pulse drain 240A around $8@1000. Mighty. (Hmm 46.5A at 41 mOhm: 71W loss, sinkable from that case,and in half bridge mode it's only half the effort).
BUT there seem to be IGBTs with two or three times the current rating at 650V. But I think they might switch slower, so the PWM drive for BLDC motors doesn't work as well and the losses become a problem. And there is also SiC technology. I'm mostly foreign to all that high power stuff, so can someone in the know enlighten us?