What is GaN, and why are new chargers so much smaller?
Gallium nitride is a semiconductor material replacing silicon in the switching components of power supplies — and its properties allow chargers to be considerably smaller, cooler and more efficient at the same output.
How a charger works. Mains electricity is converted to low-voltage direct current by switching it on and off extremely rapidly and smoothing the result. The speed of that switching determines how large the other components — particularly the transformer and capacitors — need to be. Faster switching allows smaller components, which is the key relationship.
What gallium nitride changes. Compared with silicon, GaN has a wider bandgap, allowing it to:
Switch much faster, permitting dramatically smaller magnetic components.
Handle higher voltages in a smaller device.
Waste less energy as heat, because switching losses are lower.
Tolerate higher temperatures.
The compounding effect. Less waste heat means less cooling and less spacing required, which allows tighter packing, which shrinks the enclosure further. This is why the size reduction is much larger than the component difference alone suggests.
What this means practically:
A GaN charger delivering high wattage can be a fraction of the size of an older silicon equivalent, and noticeably lighter.
Multiple ports at high combined output become feasible in a portable device, which is why one small GaN brick can replace a laptop charger and two phone chargers.
Less heat, which is better for the charger and for whatever it is next to.
Slightly better efficiency, so marginally less electricity wasted.
What to check when buying:
Total output versus per-port output. A charger rated at a high total frequently cannot deliver its maximum from one port while others are in use, and the split when ports are shared is the specification people overlook.
Supported protocols — USB Power Delivery is the standard, and proprietary fast-charging schemes may be needed for particular phones.
Safety certification, since uncertified high-power chargers are a genuine hazard.
SiC (silicon carbide) is a related wide-bandgap material used more in high-power applications such as vehicle charging.