Silicon, GaN and SiC at 20W
What the materials inside a charger really change — and why, at 20W, the result matters more than the label
Gallium nitride (GaN) and silicon carbide (SiC) are "wide-bandgap" semiconductors that can switch faster and handle higher fields than silicon, which lets designers shrink chargers and cut losses — especially at higher power. At 20W the gains are modest: Apple's own 20W adapter uses a silicon controller with no GaN parts and measured 85.5–89.7% efficient in independent testing. SiC appears in some 45W-and-above chargers; we found no 20W SiC charger on the market. Compare measured results, not materials.
In 30 seconds
- Three materials, three different things. Silicon (Si) is the long-standing standard. Gallium nitride (GaN) and silicon carbide (SiC) are newer, "wide-bandgap" materials. Silicon carbide is not silicon, and it is not GaN.
- GaN's strength is speed. It switches efficiently at high frequency, so magnetics and capacitors can be smaller. That pays off most at 30W and above. 12
- SiC's strength is high voltage. It dominates at 650 V and above in high-power systems; in chargers it has appeared recently in some 45–65W models. No 20W SiC charger was found. 34
- Apple's 20W adapter is silicon. ChargerLAB found no GaN components in its 2023 teardown. 5
- No material makes an iPhone charge faster. Speed is set by the power level agreed and the iPhone's demand.
In three minutes
Why materials matter at all
Inside every USB-C charger, a transistor switches mains-derived high voltage on and off tens or hundreds of thousands of times per second, feeding a small transformer. Each switch event wastes a little energy, and the transistor's resistance wastes more while it conducts. Two things follow:
- Faster, cleaner switching means less loss per cycle, so the charger can switch at a higher frequency — and higher frequency allows a smaller transformer and capacitors.
- Higher breakdown strength means a transistor of a given voltage rating can be smaller with lower resistance.
Wide-bandgap materials improve both. How much that matters depends on power level, voltage, and how well the rest of the design — transformer, layout, control, cooling — is executed.
The materials side by side
Comparison of silicon, silicon carbide and gallium nitride on bandgap, critical electric field, electron mobility and thermal conductivity.
| Property | Silicon (Si) | Silicon carbide (4H-SiC) | Gallium nitride (GaN) |
|---|---|---|---|
| Bandgap (eV) | 1.1–1.12 | ~3.2 | 3.4–3.43 |
| Critical electric field (MV/cm) | 0.3 | 3.0–3.5 | 3.3 |
| Electron mobility (cm²/V·s) | 1,450–1,500 | ~700–900 | ~1,500 bulk; up to ~2,000 in the 2DEG channel of a HEMT |
| Thermal conductivity (W/cm·K) | 1.5 | ~5 | 1.3 |
Values from distributor technical articles (Newark/element14; Richardson RFPD), which differ slightly from each other; ranges are given where they do. 36 Read the table as direction, not precision.
What it means in practice:
- Bandgap and critical field — roughly ten times silicon's for both wide-bandgap materials — allow thinner, smaller, lower-resistance devices at a given voltage.
- GaN's high-mobility channel gives very low switching loss, which is why it is chosen for compact, high-frequency chargers.
- SiC's thermal conductivity — over three times silicon's — makes it strong where heat must leave a device fast, as in electric-vehicle and industrial power.
Where each appears in chargers
| Material | Typical voltage class in chargers | Where it shows up | Evidence |
|---|---|---|---|
| Silicon MOSFETs and integrated silicon switchers | Up to ~800 V | The majority of 5–20W chargers, including Apple's 20W | 57 |
| GaN HEMTs (often integrated with a controller) | 650 V and 700–750 V parts | Compact 20–140W chargers; a dozen 20W-class GaN controller ICs existed by 2023 | 28910 |
| SiC MOSFETs | 650–800 V parts in chargers | Some 45–65W chargers, mostly Chinese brands, since 2025–26; SiC Schottky diodes in power-factor stages of higher-power units | 41112 |
Distributor guidance places SiC at 650 V and above and GaN mainly below 650 V; in practice both appear around 650–800 V in chargers. 324
The 20W reality
Apple's 20W adapter is the clearest reference. ChargerLAB's teardowns found a custom Power Integrations controller — a ZN1461C with a separate protocol chip in 2021–22 units, then a single ZN1535C integrating the switch, controller and protocol in the 2023 A2940 — and "cannot find any GaN components". 5137 It measured 85.52–89.73% efficient at 220 V, with ChargerLAB rating efficiency "average" and the overall product dependable. 14 Size: about 41.5 × 42.5 × 27 mm, 58.5 g. 14
GaN 20W chargers do exist and some are smaller. Spigen's GaN ArcStation Pro 20W weighs 42 g; Xiaomi's 20W uses a JoulWatt controller with integrated GaN at 40.5 g. 1516 But being GaN guarantees neither better efficiency nor cooler running: one independent test of a GaN 20W charger measured wall-to-device efficiency of 79.6–81%. 17 That measurement included the cable and device path, so it is not directly comparable with ChargerLAB's adapter-only figures — which is exactly the point: compare measured results under the same method.
Is silicon carbide sensible in a 20W charger?
Technically, a SiC switch can run a 20W flyback. Whether it is sensible is another matter:
- Voltage: a universal-input 20W charger needs a primary switch rated around 650–800 V — within reach of silicon, GaN and SiC alike. SiC's headline advantage is very high voltage and high power, which a phone charger doesn't need. 3
- Market evidence: ChargerLAB's 2026 survey of SiC chargers from 26 brands found the lowest-power example at 45W. We found no 20W SiC charger. 4
- Where SiC appears instead: as Schottky diodes in power-factor-correction stages above about 100W, where they cut recovery losses. 4
- Labelling caution: "SiC" on a box could refer to a diode, a co-packaged switch or marketing. Only a teardown or the maker's bill of materials shows what is inside.
So, for a 20W iPhone charger, SiC is unusual and offers no established advantage. If a 20W charger claims it, ask what component is silicon carbide, and for measured efficiency and temperature.
So what should you look for?
Not the material on the box. Look for:
- Measured efficiency at your mains voltage, across loads, with a stated method.
- Measured surface temperature after an hour at full load, with ambient stated.
- Size and weight if you travel.
- A verifiable safety registration for the exact model (in India, BIS — how to check).
- Warranty and support you can actually reach.
For engineers
E1. Device structures
- Silicon MOSFET — vertical or superjunction structures dominate 600–800 V switching; in low-power adapters the switch is often monolithically integrated with the controller (Power Integrations InnoSwitch family; Apple's custom ZN parts). 85
- GaN HEMT — lateral device with a two-dimensional electron gas channel; in chargers usually enhancement-mode, frequently co-packaged with the controller (Power Integrations PowiGaN 650/750 V; Navitas NV9586 600 mΩ with QR controller for ~25W; Southchip SC3055 650 V GaN + QR for 20W; JoulWatt JW15158B). 281016
- SiC MOSFET — vertical; in recent 45–65W chargers at 700–800 V, e.g. INGACOM IGC360R075X1P (750 V) in a 45W unit; Si-Power SP9477 co-packages a 700 V / 380 mΩ SiC device with a QR controller. 41112
E2. Topology at 20W
Most 20W USB PD adapters are quasi-resonant (QR) flyback converters with synchronous rectification on the secondary and secondary-side regulation (needed for PD voltage changes), using an optocoupler or a safety-rated isolated digital link such as Power Integrations' FluxLink. 82 Active-clamp flyback (ACF) recovers leakage energy and enables zero-voltage switching at up to 1.5 MHz (TI UCC28782), but commercial ACF parts target ~30–45W and above; Power Integrations' InnoSwitch4-CZ with ClampZero starts at 42W enclosed. 19 Apple's A2940 uses a QR flyback-class integrated design with a Toshiba TPN1200APL (100 V, 9.8 mΩ) synchronous rectifier. 5 Asymmetric half-bridge at 20W: no evidence found.
E3. Why GaN's advantage scales with power
Switching loss scales with frequency, voltage swing and device charge. At low power, conduction loss in a modest-size silicon device and transformer losses can dominate, and a well-optimised silicon QR flyback runs at moderate frequency with acceptable magnetics. As power rises, silicon designs must either grow or accept higher switching loss; GaN's lower charge per switching event lets frequency — and therefore power density — rise without the loss penalty. This is inferred from device physics and supported by where GaN concentrates in the market; we found no controlled 20W GaN-versus-silicon comparison on the same enclosure. 21
E4. Selection criteria ERONIX applies
Topology and device selection for any 20W platform is judged on measured outcomes: average efficiency at 230 V and 115 V; no-load draw; hotspot temperature after 60 min at full load in 25°C and 35°C ambient; EMI margin; transient response; component derating; supply security; and cost at production volume. A well-executed silicon design may outperform a poorly executed GaN one. See 09_SI_GAN_SIC_DECISION.md for the decision record.
Myths
"GaN chargers charge iPhones faster." The iPhone draws what it requests at the agreed power level — ~18–19.5W on any compliant 20W charger. 1418
"Silicon carbide is a kind of silicon." It is a distinct compound semiconductor with very different properties. 3
"Wide-bandgap automatically means more efficient." Only measured results show that; a GaN 20W charger has been measured below Apple's silicon adapter, though on a different method. 1714
"Apple's charger is old technology because it isn't GaN." Apple's 20W uses a highly integrated custom controller and measures well. 514
Questions people ask
Is a GaN charger worth it for an iPhone? At 20W, GaN mainly offers smaller size. Charging speed is the same. At 30W and above — especially multi-port chargers — GaN's size and efficiency benefits become more meaningful.
Are SiC chargers better than GaN chargers? They target different strengths: SiC excels at high voltage and heat; GaN at high-frequency switching. In consumer chargers, both appear mostly at 45W and above. Compare measured efficiency and temperature, not the material.
Does Apple use GaN in its chargers? ChargerLAB found no GaN components in Apple's 2023 20W adapter (A2940). 5 Apple's larger adapters vary; this page covers 20W only.
What semiconductor does Fermi20 use? Fermi20 has a GaN power stage.