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So GaN chargers seem to offer more power in a more compact form-factor.

However, I've been unable to find more information that "they use GaN rather than Si". Which tells me precisely nothing.

What components use this new material and what about it makes it superior in this use case?

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    \$\begingroup\$ They use GaN switching MOSFET transistors which allow higher frequencies and have lower weight for the same power. Higher frequency means smaller lighter transformers/inductors. \$\endgroup\$ Dec 3, 2022 at 14:54
  • \$\begingroup\$ See en.wikipedia.org/wiki/Flyback_converter for more details of why the transistor and transformer are important. \$\endgroup\$ Dec 3, 2022 at 14:57

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Without getting too deep into the details, GaN is what's called a wide-bandgap semiconductor, which gives it a few advantages over silicon. (There is actually another major wide bandgap semiconductor, silicon carbide (SiC), but for reasons I won't go into now it's primarily used for very high-power applications, not low-power phone chargers.)

GaN FETs* can be much smaller for the same current and voltage handling capabilities as Si ones, which has a major advantage: it drastically lowers the FETs' parasitic capacitance, which means you can run them at much higher frequencies without significantly worse losses. This higher operating frequency means you can use smaller magnetics to achieve the same efficiency, or higher efficiency with the same magnetics. (You can also use smaller capacitors when the frequency is higher, but the magnetics--inductors and transformers--are the largest components in a switching converter.)

You may also choose to make the GaN FETs the same size as the silicon ones, to get lower on-resistance and thus higher efficiency that way--most commonly, though, you'll target a balance of the two effects, with both a lower on-resistance and a higher frequency of operation.


*An aside of minor importance: GaN FETs, as they currently exist, are not MOSFETs. Your typical GaN "MOSFET" is actually a low-voltage high-current Si MOSFET in cascode with a high-voltage high-current GaN HEMT. I won't go into what exactly an HEMT is because I don't fully understand it myself, but it's a type of transistor only possible with GaN and other semiconductors with similar structure. HEMTs are kind of like JFETs in that they're always depletion mode devices, so a cascode is used to "convert them into enhancement mode" so they can be driven like normal MOSFETs.

HEMTs aren't necessarily used just because they're "better" than MOSFETs (whether they are or not is arguable); rather, no one has yet worked out how to economically manufacture MOSFETs on GaN. We might not be too far off from that, but we're not quite there yet.

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