---
title: "GaN vs silicon"
question: "Why are USB-C chargers going GaN?"
url: "https://nearfieldnotes.com/videos/gan-vs-si/"
site: "Near Field Notes"
video: "https://nearfieldnotes.com/media/gan-vs-si/full.mp4"
duration: "2:02"
date: "2026-11-04"
note: "https://nearfieldnotes.com/notes/gan-vs-si/"
---

# GaN vs silicon (video)

Why are USB-C chargers going GaN?

2:02, with sound. [Read Note 11](https://nearfieldnotes.com/notes/gan-vs-si/) for the full answer, with figures, conditions and sources.

## Transcript

Same 65 W, same maker. So why is the GaN charger 43% smaller?

Inside each is a flyback converter, built around one switch.

In a typical silicon design, it chops 170 V about 66,000 times a second.

Every flip turns a little energy into heat. µJ per flip × flips per second = watts. In a sealed box.

Swap only the switch. Silicon: 1.7 µJ of heat per flip. GaN: 0.4 µJ.

Why such a big difference?

GaN holds about 10x the volts per µm. So 650 V fits in a far smaller switch, with less charge to move.

To turn on, silicon's gate takes 27 nC at 12 V. GaN's takes 2 nC at 6 V.

That's 0.32 µJ every flip, against 0.01 µJ.

With the same driver, silicon's drain is down in 13 ns. GaN's, in 3 ns.

The biggest piece is the charge stored on the drain. Silicon holds 94% of it below 25 V.

So even at the 80 V valley, it dumps 1.4 µJ into itself. GaN dumps 0.4 µJ.

Bigger chargers put two switches on one leg. Silicon's body diode must be emptied first: a 49 A spike, ~1,000 µJ a flip.

GaN has no body diode. 15 A, 18 µJ.

The catches: a gate rated to just 7 V, a 3 V drop running backwards, and no avalanche rating.

That's why many GaN chips come with the driver built in.

Back in the charger, GaN can flip 4x as often for the same switch heat.

A quarter of the energy per flip means a smaller transformer.

The bulk capacitor gets no help from GaN. It carries the charger between the wall's peaks, 120 times a second.

GaN got cheap, the driver got built in, and USB-C made one small charger worth buying.

---

Source: https://nearfieldnotes.com/videos/gan-vs-si/