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Comment by baybal2 | Hacker News Reader

I am not an professional EE, but a person who professionally works on circuits from time to time.

That's absolutely not the case. The higher is the switching frequency, they higher are the switching losses in a MOSFET.

MOSFET is an electrostatic device, the charge needs to both go in, and out from the gate. The more switching, the more current goes through the gate back-and-forth.

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You're talking about different things. A slow FET has a slow rise time. It spends more time crossing through the inefficient region between fully off and fully on. Switching frequency is how often you cross in one direction.

Up to a point, you can decrease total converter loss by trading conduction loss for switching loss by increasing frequency and resizing components. After that point, you start losing efficiency again. There's a sweet spot.

Yes, I see your nickname. That's the case if we go into details.

I think he specifically means high-end, high-frequency power FETs, since all the rage today is about them.

I would add that there is no real need for super-high-end switches in EVs, and component size for them is not a huge premium. There is no shortage of smart inverter topologies which achieve very good size, and efficiency without using any kind of fancy GaN of SiC switches. They will not be as small as them on the lower end, but around 100kw there is virtually no difference.

It's not a detail. It's a more complete picture. Both of your comments are different slices of the same pie.

I don't see anything written above that pertains specifically to any type of FET.

Your last paragraph is a new topic. It's true that Si can be as efficient as SiC and GaN, despite what the marketing usually says. But there are other benefits to new materials. They already support higher voltages with planar technology, and 3D will increase that further. Gate driving will get easier and more rugged.

> Your last paragraph is a new topic. It's true that Si can be as efficient as SiC and GaN, despite what the marketing usually says. But there are other benefits to new materials. They already support higher voltages with planar technology, and 3D will increase that further. Gate driving will get easier and more rugged.

There are 1000V+ silicon switches today which are not as fast, but have for, for example, very good RDSon. 1000V I think is an upper limit one would go for passenger car EV motors.

True, but even GaN will eventually exceed that, and there are other applications that will benefit.

thanks for addressing things with far more patience than i would have.

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