Gallium nitride (GaN) is changing the way engineers approach power conversion, enabling higher switching frequencies, greater efficiency, and higher power density than conventional silicon MOSFETs in many applications. But where does GaN really outperform silicon, and when does it make engineering and economic sense to adopt it? In the first episode of EPC GaN Q&A LIVE, EPC CEO Alex Lidow answers engineers' questions about GaN versus silicon, covering voltage ranges, switching losses, power density, transient response, PCB layout, parasitic inductance, gate drive, reliability, cost, and the comparison with silicon carbide. The discussion provides practical guidance for engineers evaluating GaN for next-generation power conversion systems.

1. What is the real advantage of GaN over silicon MOSFETs?

GaN is smaller, faster, lighter, and more reliable, and in most cases it can reduce the overall system size and cost significantly. GaN FETs have significantly lower R_DS(on) than silicon FETs for a comparable die area, as well as much lower switching-related charge and capacitance. This combination enables faster and more efficient switching while maintaining low conduction losses. GaN devices also do not have a body diode, eliminating reverse-recovery charge and the associated losses. These characteristics can enable power converters that are more efficient, smaller, and lighter.

2. At what voltage and power levels does GaN outperform silicon?

GaN can provide an advantage across essentially all voltage and power levels where its characteristics can be exploited. The important question is where GaN stops and silicon carbide begins.

Around 700–800 V and above, silicon carbide becomes increasingly attractive, while below that range GaN can outperform silicon, extending down to very low voltages.

For EPC, the comparison extends from approximately 150 V down to 18 V, where GaN devices show a substantial resistance advantage over silicon devices of comparable size.

Switching performance is also important. At frequencies above roughly 100 kHz, GaN can provide significantly lower switching losses, while also enabling a smaller solution.

EPC's Gen 7 low-voltage portfolio extends the GaN advantage to 40 V, 25 V, and 18 V devices. The supporting technical material also notes that EPC's 100–200 V FETs provide attractive figures of merit for higher-voltage conversion architectures.

3. Why is GaN better than silicon at high switching frequencies?

When a power transistor turns on and off, energy is required to charge and discharge its input and output capacitances. GaN requires significantly less charge than silicon, so less energy is consumed during each switching cycle.

The result is a device that can switch faster, requires less energy to switch, and produces lower switching losses.

GaN has significantly lower C_OSS, which reduces the energy required to charge and discharge the device during each switching cycle. Its lower gate charge also enables sharper and faster switching edges, further reducing switching losses.

4. What are the main differences between GaN and silicon in terms of R_DS(on), gate charge, and switching losses?

GaN benefits from the high electron mobility of the material and its ability to withstand higher electric fields in a smaller device.

This allows the device to be smaller while maintaining low resistance. The smaller device also has lower output capacitance, while the high electron mobility results in very low input capacitance.

The result is a device that requires less charge to switch, has less output charge to charge and discharge, and occupies less physical space.

GaN can therefore combine low R_DS(on) and low gate charge simultaneously. Compared with silicon FETs of similar voltage capability, the lower gate charge also means that less gate current is required to achieve a given switching speed, resulting in lower switching losses.

5. Why can GaN achieve higher power density than silicon?

The GaN chip itself can be much smaller for the same power capability, but the biggest system-level savings often come from the other components in the converter.

Higher switching frequencies allow capacitors and inductors to become smaller. In applications such as motor drives, bulky electrolytic capacitors can in some cases be replaced by much smaller ceramic capacitors.

As the switching frequency increases, the entire system can therefore become smaller.

The lower R_DS(on) achievable in a given die area allows the semiconductor itself to be smaller, while the lower capacitances enable higher switching frequencies and therefore smaller inductors and transformers.

6. How does higher switching frequency reduce the size of inductors and capacitors?

Every switching cycle stores energy in capacitors and inductors. At a higher switching frequency, each individual packet of energy is smaller, so the required energy storage—and therefore the component size - can be reduced.

EPC's motor-drive examples demonstrate this evolution: conventional MOSFET-based designs with large capacitors can be replaced by increasingly integrated GaN solutions using ceramic capacitors and much smaller power stages.

As switching frequency increases, inductors and capacitors need to store less energy and can therefore be made smaller. This reduction in passive-component size contributes significantly to the overall reduction in converter footprint and volume.

7. Is GaN actually more efficient than silicon, or does it depend on the application?

It depends on the application. If GaN is used at a very low frequency, or essentially as a DC pass device, its high-speed switching advantage is largely neutralized.

In those applications, the main consideration becomes on-resistance, and an older silicon MOSFET may provide adequate performance at lower cost.

However, in applications where high switching frequency is important, GaN can provide a significant efficiency advantage.

The actual efficiency depends on multiple factors, including the application, topology, operating conditions, dead time, schematic, PCB layout, gate-drive selection, and the specific FET selected.

8. Does GaN always reduce power losses compared with silicon?

Not always. If you compare GaN and silicon devices with similar on-resistance, GaN will generally provide lower losses when operating above approximately 100 kHz.

At much lower frequencies, such as 20 or 50 kHz, the difference can become much smaller and may be difficult to distinguish.

The reduction in power losses therefore depends on the application and operating conditions rather than being automatic in every design.

9. Can GaN improve transient response in power converters?

Yes. Because GaN allows converters to operate at much higher switching frequencies, the converter can respond to load changes much faster.

With silicon MOSFETs, switching losses can limit the practical operating frequency. GaN can extend operation into the megahertz range, allowing much faster control and transient response.

This is particularly important for demanding applications such as AI processors, where load transients can be extremely fast.

Higher switching frequency can support a higher control-loop bandwidth, which can directly improve transient response in power converters.

10. Is GaN more difficult to design with than silicon? What do engineers need to change?

If GaN is used for high-speed switching, engineers need to pay much more attention to parasitic elements, particularly parasitic inductance.

At low switching speeds, PCB parasitics may have relatively little influence. At very high switching speeds, however, they can become a dominant part of the circuit performance.

The solution is better PCB layout discipline and careful control of parasitic inductance.

GaN designs also require appropriate gate-drive considerations. However, many gate-driver ICs are specifically designed for GaN, and careful layout of both the gate loop and power loop is particularly important for minimizing parasitic inductance.

11. What are the main PCB layout and EMI challenges when designing with GaN?

One of the most important PCB considerations is common-source inductance. Excessive common-source inductance can oppose the gate-drive signal, slowing the device or causing ringing.

Power-loop inductance is also critical because it can produce voltage overshoot during fast switching.

Both forms of parasitic inductance can contribute to EMI, particularly when they generate ringing.

Because GaN enables very fast switching edges, the power loop and gate loop should be kept extremely tight, with decoupling capacitors placed close to the switching devices. Excessive parasitic inductance can cause voltage spikes and ringing.

12. Why are parasitic inductances more critical with GaN?

The fundamental relationship is V = L × di/dt. Because GaN can switch current extremely quickly, the di/dt can become very large.

Even a very small parasitic inductance can therefore generate a significant unwanted voltage.

For example, with 1,000 A changing in one nanosecond, even one nanohenry of parasitic inductance would generate 1,000 V. This illustrates why engineers need to push parasitic inductance down to extremely low levels in very high-speed designs.

The faster switching speed and lower capacitances of GaN make parasitic inductance more influential than in slower silicon MOSFET designs.

13. What gate-driver voltage should be used for an EPC GaN transistor?

For EPC GaN transistors, approximately 5 to 5.25 V is the ideal gate-drive voltage for turn-on.

For turn-off, 0 V should be used.

This recommendation is specifically for EPC GaN transistors and should not automatically be generalized to GaN devices from other manufacturers.

The supporting EPC technical material specifies 0 V for OFF and approximately 5–5.5 V for ON. For EPC GaN FETs, negative gate voltage is not required or recommended, and gate voltages significantly above approximately 5 V provide little additional benefit.

14. What are the key differences in degradation mechanisms and long-term reliability between GaN and silicon?

GaN has been extensively studied for reliability because engineers need to understand the material and its degradation mechanisms before adopting it in demanding applications.

As a wide-bandgap semiconductor, GaN has strong chemical bonds in its crystal lattice and is less sensitive to certain temperature-related effects than silicon.

The most important considerations for long-term reliability are operating within the specified voltage and current limits and managing thermomechanical stress.

Thermomechanical stress between the device and the external environment can eventually become a wear-out mechanism, so the thermal and mechanical mission of the device needs to be considered during the design.

The EPC technical material further explains that EPC GaN FET wear-out does not continuously increase with temperature in the same manner as some conventional expectations might suggest. It emphasizes observing datasheet limits and considering thermal cycling when designing for long operating life.

15. What are the main disadvantages of GaN, and where is silicon still the better choice?

There are applications where engineers may choose silicon simply because they do not need the additional performance provided by GaN.

If an application does not benefit from higher switching frequency, higher efficiency, or higher power density, the additional performance of GaN may not justify changing an existing design.

Technically, a key disadvantage of GaN is the higher voltage drop during reverse-current conduction, which can increase dead-time losses. Silicon can therefore remain attractive in applications where high efficiency or power density are not important, particularly when very low cost is the primary consideration.

16. Is GaN worth the higher cost compared with silicon, and when does it make economic sense to switch?

GaN is worth the cost when the additional performance provides a meaningful advantage. If a legacy design already meets its requirements, there may be little reason to change it.

If performance is important - for example, to gain market share through better efficiency, smaller size, or higher performance—GaN can provide that additional capability.

If the application is primarily cost-driven, engineers need to evaluate whether the system-level advantages of GaN justify the investment.

EPC's technical material emphasizes that GaN FETs are not necessarily more expensive than silicon MOSFETs in every comparison. More importantly, engineers should evaluate the complete system cost, including heatsinks, PCB size, capacitors, inductors, chassis size, and potentially improved reliability.

17. How can GaN reduce the overall Bill of Materials (BOM) cost?

Even if the GaN FET itself costs more than a comparable silicon device, the system can become less expensive because higher switching frequency allows smaller passive components.

Smaller inductors and capacitors can reduce both component cost and the overall size of the PCB and system.

The overall BOM should therefore be evaluated at the system level. Increasing switching frequency can reduce the size and cost of magnetics and can also reduce the number or size of capacitors required.

18. How should engineers select the right GaN transistor for a converter?

For a given converter, there can be multiple suitable EPC GaN devices. Engineers can narrow the selection using an EPC device-selection calculator, evaluation boards, and simulation. The choice should be based on the requirements of the converter and the relevant device characteristics.

19. How does GaN compare with silicon carbide, and when should an engineer choose GaN instead?

Silicon carbide begins to have an advantage at approximately 750 V and above because its vertical device structure is well suited to higher-voltage operation.

GaN has important advantages at lower voltages because its lateral structure allows low on-resistance as well as the integration of additional functions.

This integration makes it possible to create highly integrated motor drives and power stages that are difficult to achieve using conventional silicon or silicon carbide devices.

In general, below approximately 650 V, GaN can be the better choice, while above that range silicon carbide becomes increasingly attractive.

20. Can GaN replace silicon MOSFETs in all power converters?

According to the supporting EPC technical material, GaN can potentially replace silicon MOSFETs in a very broad range of power converters. However, some applications may continue to use silicon for several years, particularly low-speed linear regulators, pass elements, ultra-low-cost products, and applications where high performance is not required.

Maurizio Di Paolo Emilio, Director of Global Marketing Communications at EPC