GaN vs SiC: AI Power and EV Charger Technology Guide

Introduction: The Wide Bandgap Semiconductor Revolution

Data center and EV growth has driven unprecedented demand for high-efficiency power conversion. As silicon devices near their limits, wide bandgap semiconductors—GaN and SiC—enable next-generation power systems. But which fits where?

This article examines the technical boundaries and application criteria for GaN and SiC in AI server power supplies and automotive onboard chargers (OBC).

Understanding GaN and SiC: Material Properties and Performance

What Makes Wide Bandgap Semiconductors Special?

GaN and SiC offer key advantages over silicon:

• Higher breakdown field: Thinner drift regions, lower on-resistance
• Higher thermal conductivity: Better heat dissipation, higher operating temperatures
• Faster switching: Lower switching losses, higher frequency operation
• Lower switching losses: Better system efficiency

GaN Key Characteristics

Gallium Nitride HEMTs excel in:

• Fast switching (hundreds of kHz to MHz)
• Low voltage applications (≤650V)
• Compact, high power density designs
• Lower gate drive requirements vs. SiC

GaN devices feature low gate charge (Qg) and output capacitance (Coss), enabling efficient high-frequency switching. Lateral structure provides low parasitic inductances.

SiC Key Characteristics

Silicon Carbide MOSFETs are optimized for:

• Higher voltages (1200V, 1700V+)
• High temperature operation (>175°C)
• High current handling
• Superior thermal conductivity (3× vs. silicon)

SiC’s vertical structure enables excellent current density and avalanche capability. Mature oxide technology provides stable threshold voltage and gate oxide performance for automotive reliability.

AI Power Systems: Why GaN Dominates Data Centers

The AI Server Power Challenge

Modern AI accelerators demand extraordinary power delivery. A single NVIDIA H100 GPU consumes up to 700W; next-gen chips approach 1000W. Data centers require power systems that are:

• Extremely efficient (every point matters at megawatt scale)
• Highly compact (rack space is expensive)
• Capable of rapid transients (AI workloads vary dramatically)

GaN in PFC and DC-DC Conversion

GaN devices deploy in two critical stages:

1. Power Factor Correction (PFC)

PFC converts AC input (208V/277V) to regulated DC bus (380-400V). GaN enables:

• Totem-pole bridgeless PFC: Eliminates diode bridge, reduces losses 0.5-1%
• Higher frequencies: 100-200kHz (vs. 65kHz silicon) shrinks magnetics 40-50%
• Better transient response: Fast switching handles AI inference bursts

Manufacturers report 96% to 97.5% efficiency when transitioning from silicon to GaN.

2. DC-DC Conversion

DC-DC steps down to processor voltages (0.7-1.2V at hundreds of amperes). GaN enables:

• Multi-phase buck converters: 500kHz-1MHz enables smaller inductors, faster transients
• Tight regulation: Meets ±1-2% voltage tolerance of AI processors
• Compact size: Critical for blade/1U servers

Why Not SiC for AI Power?

SiC is less optimal for AI servers because:

• Server power operates ≤650V, where GaN has lower switching losses
• SiC’s higher gate charge needs complex drivers, adding cost
• GaN’s high-frequency performance enables compact designs for dense racks
• GaN at 650V is cost-competitive with SiC, especially with reduced passive costs

Automotive Onboard Chargers: SiC’s Stronghold

The EV Charging Challenge

EV onboard chargers (OBC) convert AC to DC for battery packs. Modern EVs need:

• 7kW to 22kW power
• 85-265V AC input (single or three-phase)
• 200V to 800V output
• 15-year reliability across automotive temperatures
• Compact design

Why SiC Dominates in OBC

1. Voltage Requirements

OBCs use 400V or 800V DC link voltages, requiring:

• 1200V devices for 400V systems
• 1200V-1700V devices for 800V systems

SiC MOSFETs offer lower RDS(on) than silicon and better high-temperature performance than GaN. While 650V GaN exists, limited voltage margin makes it unsuitable for automotive robustness requirements.

2. Thermal Performance

Automotive environments demand:

• -40°C to +85°C ambient operation
• 175°C junction temperatures under peak loads
• Continuous thermal cycling

SiC advantages:

• Thermal conductivity: 490 W/m·K vs. 130 W/m·K for GaN
• Operating temperature: 175°C vs. 150°C for GaN
• Cooling: Smaller heatsinks possible

3. System Integration

SiC enables compact OBC designs:

• Vienna rectifier PFC: 98%+ efficiency, reduced EMI
• LLC converters: Efficient zero-voltage switching
• Bidirectional power: V2G/V2H with minimal circuitry

Tier 1 suppliers report power density improvements from 1.5 kW/L to 3-4 kW/L transitioning from silicon IGBT to SiC.

Could GaN Work in OBC?

GaN faces challenges in OBC:

• Voltage margin: 650V GaN provides limited headroom for 400V systems
• Thermal limits: Lower thermal conductivity needs aggressive cooling
• Reliability: Less AEC-Q101 data than SiC
• Cost: SiC pricing has narrowed GaN’s advantage

GaN may suit auxiliary power modules or low-voltage DC-DC converters in EVs.

Efficiency, Cost, and Reliability Trade-offs

Efficiency Comparison

AI Server PSU (650V, 3-7kW)

• Silicon: 95.5-96.5%
• GaN: 96.5-97.5%
• SiC: 96.0-97.0%

Winner: GaN (superior high-frequency performance)

OBC (800V, 11-22kW)

• Silicon IGBT: 94.0-95.5%
• SiC: 96.0-97.5%
• GaN (650V, 400V systems only): 95.5-96.5%

Winner: SiC (voltage capability, thermal performance, reliability)

Total System Cost

System cost includes:

• Semiconductor devices
• Gate drivers and control
• Passive components
• Thermal management
• PCB and assembly

GaN Cost Advantages

• 20-30% smaller magnetics
• Simpler gate drivers
• Reduced EMI filtering
• Smaller enclosures

SiC Cost Advantages

• Usable body diode eliminates antiparallel diodes
• Simpler cooling systems
• Simplified protection circuits
• Improving 200mm wafer pricing

At 100K+ annual volumes, GaN and SiC system costs are comparable in their respective sweet spots.

Reliability Considerations: The 15-Year Question

Automotive applications require 15-year, 150,000+ mile reliability. Key metrics:

SiC Reliability Advantages

• Mature qualification: Widely available AEC-Q101 qualified devices
• Gate oxide stability: Significant quality improvements over past decade
• Field experience: Deployed in EVs since 2014 (Tesla Model S)
• High-temperature operation: Proven stability at 175°C junction temperature

GaN Reliability Challenges

• Limited automotive qualification: Fewer AEC-Q101 qualified devices
• Thermal cycling concerns: Different thermal expansion coefficients
• Threshold voltage stability: Ensuring Vth stability over temperature and lifetime
• Field experience gap: Less automotive deployment history than SiC

GaN reliability in consumer and industrial applications (5-10 year lifetimes) is well demonstrated, making it suitable for data center equipment with typical 5-7 year refresh cycles.

The Decision Matrix: Choosing Between GaN and SiC

Choose GaN When:

• Operating voltage ≤650V
• High-frequency operation (>100kHz) benefits size reduction
• Power density is critical
• Application lifetime is 5-10 years
• Fast transient response is essential
• Controlled temperature environments

Choose SiC When:

• Operating voltage exceeds 650V
• High ambient temperatures expected (>70°C)
• 15+ year lifetime required (automotive)
• Bidirectional power flow needed
• Robust avalanche capability important
• Maximum thermal conductivity beneficial

Application-Specific Recommendations

AI Server Power Supplies

• PFC: GaN (totem-pole bridgeless, 650V)
• DC-DC: GaN (high-frequency multi-phase buck)
• Auxiliary: Silicon or GaN

400V EV Onboard Charger

• PFC: SiC (1200V Vienna rectifier or bridgeless totem-pole)
• DC-DC: SiC (LLC resonant converter)
• Alternative: GaN for low-cost designs with adequate voltage margin

800V EV Onboard Charger

• PFC: SiC (1200V or 1700V devices)
• DC-DC: SiC (LLC resonant or CLLC bidirectional)
• GaN not suitable due to voltage limitations

Future Trends: Where Are GaN and SiC Headed?

GaN Technology Evolution

• Higher voltage: 1200V GaN devices for broader applications
• Integrated solutions: Power ICs with integrated drivers and protection
• Improved thermal performance: Advanced packaging and substrates
• Cost reduction: 200mm wafers and improved yields

SiC Technology Evolution

• 200mm wafer adoption: 30-40% cost reduction
• Trench MOSFET technology: Improved on-resistance and switching
• Higher voltage platforms: 3.3kV and 6.5kV devices
• Improved oxide quality: Enhanced reliability and Vth stability

Market Convergence Points

Both technologies are evolving toward overlapping spaces:

• GaN pushing toward 1200V for more automotive applications
• SiC improving high-frequency performance for lower-power applications

By 2027-2028, the choice may depend more on specific system requirements than absolute voltage boundaries. However, material properties will continue to favor GaN for highest-frequency and SiC for highest-temperature, highest-voltage applications.

Conclusion: Complementary Technologies for Different Applications

GaN and SiC are complementary technologies, each optimized for specific requirements. The dividing line reflects fundamental material properties and system-level trade-offs:

• AI power systems benefit from GaN due to superior high-frequency performance, compact form factor, and excellent efficiency at ≤650V—matching data center power distribution requirements.
• Automotive onboard chargers benefit from SiC due to high-voltage capability, thermal performance, and proven long-term reliability—essential for automotive environments.

For designers, the key is matching device capabilities to requirements rather than following trends. As both mature and costs decrease, the winning approach is hybrid systems deploying each where it provides maximum value—GaN for high frequency and compact size, SiC for high voltage and extreme reliability.

The future of power electronics is not GaN versus SiC, but GaN and SiC together, enabling the next generation of efficient, compact, and reliable power conversion systems.