Summary. Phone and laptop chargers are switch-mode power supplies that convert 100–240 V AC mains power into low-voltage DC power at several voltage levels. Two metrics that determine the experience are efficiency (the portion of electrical energy converted into heat) and power density (power per unit volume). This review selectively examines how the Gallium Nitride (GaN) material affects these two metrics: from the physical properties of the wide-bandgap semiconductor, through the switching-loss mechanism in a quasi-resonant flyback circuit, to the figures for two 65 W reference designs published by Texas Instruments and STMicroelectronics. The results show that the main advantage of GaN is enabling higher switching frequencies to shrink the transformer; the practical increase in efficiency is much more modest than it is often advertised to be. The final section explains how to read charger specifications and compares several OH-Tech GaN models based on published specifications.
Keywords: GaN, Gallium Nitride, charger, power density, USB Power Delivery, PPS, quasi-resonant flyback, switching loss.
1. Problem statement
A charger is a switching power supply. The mains power is rectified and chopped into pulses at frequencies ranging from tens to hundreds of kilohertz, then passes through an isolation transformer before being rectified again into DC at the output. Each time the transistor turns on or off, some energy is lost. This lost energy becomes heat on the charger's casing, which is why high-power chargers are often large and hot.
Current design pressure comes from two directions. Legally, Directive (EU) 2022/2380 requires phones, tablets, headphones, and many handheld devices to use USB-C ports from 28/12/2024, and extends this requirement to laptops from 28/4/2026 [1]. Technically, the USB Power Delivery 3.1 (2021) standard raises the power ceiling of a single port from 100 W to 240 W [2]. A shared port brings a shared expectation: one charger must handle everything from headphones consuming a few watts to laptops consuming tens of watts, without being bulkier than what users are accustomed to carrying.
The question of this article is: what does GaN change at the physical level, and how many measurable benefits do those changes deliver at the charger level?
2. Physical basis of the material
Silicon has a bandgap of 1,12 eV, while GaN is around 3,4 eV (sources report 3,39–3,44 eV) [3][5]. The wide bandgap enables the material to withstand stronger electric fields before breakdown: 3,3 MV/cm in GaN compared with 0,3 MV/cm in silicon, approximately 11 times higher (Table 1).
| Specifications | Silicon (Si) | GaN |
|---|---|---|
| Bandgap width (eV) | 1,12 | 3,44 |
| Critical breakdown field (MV/cm) | 0,3 | 3,3 |
| Electron mobility (cm²/V·s) | 1.000–1.400 | 1.500–2.000 (in two-dimensional electron gas) |
| Electron saturation velocity (×107 cm/s) | 1 | 2,2 |
| Thermal conductivity (W/cm·K) | 1,5 | 1,3–2,2 |
Table 1. Some material parameters of Si and GaN. Source: EDN [3]; the range of values depends on the device structure and the literature source.
The significance of the breakdown field is clearly reflected in the Baliga figure of merit. For an ideal unipolar device, the specific on-resistance of the drift region (the voltage-blocking region) is Ron,sp = 4VB2 / (ε · μ · Ec3), where VB is the breakdown voltage, ε is the dielectric constant, μ is the mobility, and Ec is the critical breakdown field [4]. Because the critical field is raised to the third power, (3,3 / 0,3)3 ≈ 1.331. The ε · μ products of the two materials are nearly equal, because GaN has a lower dielectric constant than silicon but higher mobility. Result: at the same withstand voltage, the GaN drift region can theoretically conduct roughly 103 times better.
This number is only a theoretical approximation for the ideal drift region. Actual devices are also subject to channel resistance, contact resistance, and packaging, so the practical improvement is many orders of magnitude lower [5]. The important design implication is that, with a 650 V withstand voltage rating (a level commonly used for grid voltages up to 265 V AC, with a peak of approximately 375 V, plus reflected voltage and spikes), a GaN transistor can have a significantly smaller chip area than a silicon MOSFET with the same resistance. A smaller chip means lower parasitic capacitance, and parasitic capacitance is the main source of switching losses in Section 3.
Commercial GaN components are typically AlGaN/GaN HEMTs. At the interface between the two layers, the polarization effect creates a two-dimensional electron gas (2DEG) with a density on the order of 1013 cm-2 without requiring doping, providing a mobility above 2.000 cm²/V·s [5][6]. This lateral structure also enables gate driver and protection circuits to be integrated directly on the same chip, as in the integrated LMG3624 GaN transistor in Texas Instruments’ reference design [8].
One disadvantage is worth noting: the thermal conductivity of GaN (1,3–2,2 W/cm·K) does not exceed that of silicon (1,5 W/cm·K). GaN chargers run cooler because they generate less heat, not because they dissipate heat better [3].
3. From materials to power supply: switching loss and frequency
In a quasi-resonant flyback (QR) converter, the main switching-loss component occurs at transistor turn-on. The energy stored in the output capacitance Coss is dissipated as heat each cycle: PCoss = ½ · Coss,er · V2 · fsw [8]. This loss is directly proportional to switching frequency, so with silicon, increasing the frequency always comes at the cost of heat.
Texas Instruments' 65 W reference design provides a specific example: the energy-equivalent output capacitance of the GaN transistor is only 29 pF when the voltage transitions from 400 V to 0 V, resulting in a loss of ½ × 29 pF × (400 V)2 × 150 kHz ≈ 0,348 W at 150 kHz, equivalent to approximately 0,53% system efficiency. In practice, the figure is even lower because the circuit switches at a voltage “trough” below 400 V [8]. STMicroelectronics' documentation compares 650 V/225 mΩ GaN with 650 V/230 mΩ silicon MOSFET: the energy Eoss is approximately 1,7 µJ for GaN and 3,7 µJ for MOSFET, corresponding to 0,24 W and 0,52 W at 140 kHz [9].
Those energy savings can be “reinvested” in higher frequencies. The benefit of doing so lies in the transformer, which accounts for most of the charger’s volume. The familiar design equation for the core area product is Ap = Pt · 104 / (Kf · Ku · Bm · f · J) [7]. When power, flux density, current density, and window factor remain constant, Ap is inversely proportional to frequency f. In principle, doubling the frequency allows the core size to be halved. In practice, the reduction is smaller because flux density Bm must be reduced as frequency increases due to core loss. Texas Instruments documentation describes exactly this consequence: GaN’s high-frequency operation enables smaller inductors, smaller cores, and fewer primary turns [8].
4. Data from reference designs
Table 2 summarizes the published data of three 65 W boards from two component manufacturers.
| Criteria | TI TIDA-050072 (QR flyback) | ST EVLVIPGAN65PD (QR flyback) | ST EVLONE65W (ACF) |
|---|---|---|---|
| Power | 65 W | 65 W | 65 W |
| Switching frequency | 76–163 kHz | up to 140 kHz | up to 250 kHz |
| Dimensions | not specified in the document | 69 × 20 × 35 mm | 58 × 32 × 20 mm |
| Power density | 25,29 W/in3 | 22,1 W/in3 | 28,7 W/in3 |
| Full-load efficiency | 94,09% (115 Vac); 94,32% (230 Vac) | meets CoC Tier 2 and DoE Level VI | not specified in the document |
Table 2. Published data for 65 W reference designs using GaN. Source: Texas Instruments [8], STMicroelectronics [9]. ACF: active clamp flyback. ST density is calculated for the board without a casing.
There are three observations. First, at the same 65 W power, power density varies from 22 to nearly 29 W/in3, and the differences between the boards mainly follow switching frequency. ST concluded that active-clamp flyback (ACF) using GaN delivers nearly 30% higher power density than resonant flyback due to operating at a higher frequency [9]. Second, in terms of efficiency, ST found that a “conventional” QR flyback using GaN is 3–4% more efficient than QR flyback using silicon, while GaN QR efficiency is comparable to GaN ACF under most operating conditions [9]. Third, 94% efficiency at full load, along with standby power of only 30 mW at 115 Vac in a Texas Instruments design [8], is a less discussed but important metric for an always-connected charger.
To illustrate what a few percentage points of efficiency mean, consider the following illustrative calculation (not a measurement of a specific product). At an output power of 65 W, a charger with 90% efficiency dissipates 65 × (1/0,90 − 1) ≈ 7,2 W of heat; a charger with 94% efficiency dissipates 65 × (1/0,94 − 1) ≈ 4,1 W, about 43% less. At 30 W, those two efficiency levels correspond to approximately 3,3 W and 1,9 W.
5. Implications of reading charger specifications
Power is the product of voltage and current. A USB Power Delivery charger advertises a list of voltage levels along with the maximum current (usually 5, 9, 12, 15 and 20 V), and the device selects the level it needs. The “45 W” rating is usually only achieved at 20 V × 2.25 A; at 5 V, all PD chargers supply only 5 V × 3 A = 15 W. A device that supports only 5 V will not charge faster, even when plugged into a 45 W charger. PPS (Programmable Power Supply) mode allows the device to request a voltage within the 3.3–21 V range in 20 mV increments and a current limit in 50 mA increments, reducing the voltage conversion inside the device and helping it run cooler [2].
GaN also needs to be used in the right place. At power levels of 20 W and below, absolute losses are already small (at 90% efficiency, only about 2,2 W), so the savings from GaN are also small. Consistent with that assessment, the 20 W models in the OH-Tech lineup (OH-K20 and SR-GZ01) explicitly state in their specifications that they do not use GaN. According to the author, the advantage of GaN becomes increasingly apparent as power increases, from the 30 W range upward. Table 3 lists the currently available GaN models.
| Product code | Maximum power | Ports | Highest PD level on USB-C | Protocol / notes |
|---|---|---|---|---|
| OH-K30 | 30 W | 1 × USB-C | 20 V / 1,5 A | PD 3.0, PPS, QC 3.0 |
| OH-K26 | 35 W | 1 × USB-C | 20 V / 1,75 A | USB-C output according to PD profile |
| SR-GZ03 (Syron) | 35 W | 1 × USB-C | 20 V / 1,75 A | USB-C output according to PD profile |
| OH-K27 | 45 W | 1 × USB-C + 1 × USB-A | 20 V / 2,25 A | USB-A port: 5 V/3 A, 9 V/2 A, 12 V/1,5 A |
| OH-K28 | 67 W | 1 × USB-A | Not applicable | SuperVOOC, VOOC, Mi Turbo, SCP, FCP, QC 3.0, AFC |
Table 3. Some GaN chargers from OH-Tech and Syron. The data is based on the manufacturer's published specifications; the author has not independently tested them.
All five models list overvoltage, overcurrent, and overheat protection in their specifications, along with a 12-month warranty. Specifically, OH-K28 delivers 67 W through the USB-A port using proprietary fast-charging protocols from various smartphone manufacturers, so this output is only achieved when the device supports the corresponding protocol. The remaining models use USB-C with USB PD and support a broader range of devices, including phones, tablets, and laptops whose power consumption is within the charger’s capacity. The charger is only one link in the chain; the included cable must also withstand the corresponding current. Standard cables support 3 A, while 5 A cables must feature an E-Marker chip; this topic is analyzed in the article From USB-A to USB-C: 30 Years of Charging Cables and How to Choose the Right One.
6. Limitations
- Data source. The efficiency and power density figures come from the component manufacturers’ reference documentation (Texas Instruments, STMicroelectronics). This is useful technical documentation, but it is also promotional material for the components, with measurement conditions selected by the manufacturer.
- No independent measurements. The article does not present measurement results on OH-Tech products. All product specifications are published specifications.
- Simplified model. The analysis in Section 3 considers only losses due to output capacitance. Conduction losses, transformer core and copper losses, secondary rectifier losses, and EMI filtering requirements also affect the final result.
- Illustrative figures. The calculations in Section 4 use two assumed efficiency levels (90% and 94%) to show the order of magnitude, not measurements.
- Benefit claims. The article was prepared by OH-Tech and mentions OH-Tech’s own products.
7. Conclusion
The core benefit of GaN in chargers is not that it “runs cooler magically.” It lies in a chain of cause and effect: a wide bandgap, low parasitic capacitance, low switching loss, higher frequencies, smaller transformers, and higher power density. The efficiency improvement is real, but only on the order of a few percentage points, and most of the value manifests as a smaller, more compact charger at the same power output. For buyers, the right way to assess it is to look at the power output at 20 V, supported protocols (PD, PPS), protection layers, and included cable, rather than looking only at the two letters “GaN” on the packaging.
Frequently Asked Questions
What is GaN?
GaN stands for Gallium Nitride, a semiconductor compound of gallium and nitrogen with a wide bandgap of approximately 3,4 eV. In chargers, it is used as a switching transistor instead of silicon MOSFETs.
Are GaN chargers really cooler than silicon chargers?
At the same power, GaN chargers generally generate less heat due to lower switching losses; the difference depends on the design. However, GaN chargers are often smaller, resulting in less heat dissipation area, so the casing temperature is not necessarily lower.
What power rating should I choose for a GaN charger?
Choose a power rating equal to or higher than what the device requires; the charger will only supply what the device requests. GaN makes a clear difference from around 30 W upward, when absolute losses and transformer size become significant. At 20 W and below, the advantage is small.
What is PPS, and do I need it?
PPS (Programmable Power Supply) is a mode of USB PD that allows a device to request voltage in the range of 3.3–21 V in 20 mV increments and current in 50 mA increments. Some phones use PPS to fast charge with less heat. If your device supports PPS, choose a charger labeled PPS, for example OH-K30.
Which cable should be used with a 45 W or higher charger?
At 20 V, the 45 W charger’s output is 2,25 A, within the 3 A limit of a standard cable. For a cable required to carry more than 3 A (up to 5 A, or 100 W at 20 V), the cable must have an E-Marker chip compliant with USB Type-C.
Which GaN chargers does OH-Tech offer?
The current lineup includes OH-K30 (30 W), OH-K26 (35 W), SR-GZ03 (35 W), OH-K27 (45 W) and OH-K28 (67 W), as well as GaN charger-cable kits such as OH-B30C. Prices are available upon quotation; contact OH-Tech or a dealer for consultation.
References
- European Commission. The EU common charger (Radio Equipment Directive, Directive (EU) 2022/2380). single-market-economy.ec.europa.eu.
- USB Implementers Forum. USB Power Delivery Specification, Revision 3.1 (2021); the PPS scope according to USB-IF’s “USB Power Delivery” presentation.
- Shaukat, A. (2024, April 10). GaN vs SiC: A look at two popular WBG semiconductors in power. EDN. edn.com.
- Baliga, B. J. (1982). Semiconductors for high-voltage, vertical channel field-effect transistors. Journal of Applied Physics, 53, 1759–1764. doi:10.1063/1.331646.
- Millán, J., Godignon, P., Perpiñà, X., Pérez-Tomás, A., & Rebollo, J. (2014). A survey of wide bandgap power semiconductor devices. IEEE Transactions on Power Electronics, 29(5), 2155–2163. doi:10.1109/TPEL.2013.2268900.
- Lidow, A., de Rooij, M., Strydom, J., Reusch, D., & Glaser, J. (2019). GaN Transistors for Efficient Power Conversion (3rd ed.). Wiley. ISBN 978-1-119-59414-7.
- McLyman, W. T. (2011). Transformer and Inductor Design Handbook (4th ed.). CRC Press. ISBN 978-1-4398-3687-3.
- Texas Instruments. (2023, November). 65-W, GaN-based USB PD 3.0 USB Type-C adapter reference design (TIDA-050072, TIDUF57). ti.com.
- STMicroelectronics. (2023, October 18). Benefits of GaN in QR flyback. Presented at Digital We Days 2023, Würth Elektronik. we-online.com.
