Implementing GaN in power electronics design: key factors

Power electronics play an increasingly vital role in our era of rapid technological progress, powering everything from advanced communications networks to electric vehicles. As electricity demand surges and sustainability concerns grow, optimising power efficiency has become paramount. Wide bandgap semiconductors, particularly gallium nitride (GaN), are emerging as a game-changer in this field.

GaN power electronics offer significant advantages over traditional silicon-based solutions. They enable faster switching speeds, higher power density, and improved charging experiences, all while minimising heat generation and reducing device sizes. These benefits are driving a projected 60% annual growth in the GaN power electronics market, expected to reach $2 billion by 2025.

However, harnessing the full potential of GaN in power electronics is a complex undertaking. Designing GaN-based systems requires meticulous attention to modelling and simulation, addressing intricate physical effects ranging from thermal management to electromagnetic interference (EMI).

This article demonstrates good practices for design leaders seeking to position their teams at the forefront of wide bandgap semiconductor innovations. Here we will explore five key considerations that every power electronics engineer should address in GaN-based design processes: model and schematic design, board parasitic elements, EMI mitigation, thermal management strategies, and power module optimisation.

The challenges in accomplishing high-speed GaN applications

The widespread adoption of GaN in power electronics has revolutionised design rules, particularly for switched-mode power supplies (SMPSs). GaN transistors enable SMPS designs to achieve efficiencies exceeding 90% in high-frequency applications, significantly surpassing silicon-based alternatives. Moreover, GaN's wide voltage range adaptability makes it ideal for SMPSs that must accommodate fluctuating input voltages. This allows power electronics designers to further miniaturise devices while maintaining exceptional efficiency and switching speeds across a broad spectrum of input and output voltages.

However, GaN's superior switching speeds introduce new design complexities. The heightened voltages and faster switching edges associated with GaN lead to increased voltage spikes, unwanted electromagnetic interference (EMI), and more harmonic content in signals and noise at higher frequencies. Consequently, traditional "cut-and-try" design methods, effective for low-speed designs, become impractical for GaN-based power electronics due to several critical factors:

• Escalating prototyping costs: Building and maintaining physical prototypes in the lab has become increasingly expensive. Overstress can easily damage these prototypes, and rectifying flaws in intricate systems can be a lengthy and costly process, potentially taking months and costing millions of dollars.
• Extended time-to-market: Troubleshooting hardware bugs can be a time-consuming endeavour, often exceeding acceptable timelines for designers. Even minor modifications, such as adjusting trace dimensions, can necessitate weeks of re-spins.
• Limited testing capabilities: Comprehensive testing scenarios are challenging to achieve with physical prototypes. Injecting certain faults can damage the prototypes, while other types of defects may be impossible to introduce for testing purposes.

These challenges underscore the need for innovative design methodologies that can effectively address the complexities of GaN-based power electronics, mitigate risks, and accelerate time-to-market.

The key GaN SMPS considerations

• Prioritise accurate models and schematic design: The foundation of any SMPS design lies in the accuracy of its underlying models and the effectiveness of the schematic design tool. These initial stages are crucial for establishing a robust design framework.
• Mitigate board parasitics with post-layout simulation: Many design tools primarily focus on schematic-level simulations, which often overlook the real-world impact of circuit board parasitics. Post-layout simulation at the board level is essential for identifying and addressing these parasitic effects, minimising the need for expensive and time-consuming design revisions.
• Proactive EMI mitigation: Electromagnetic Interference (EMI) is a crucial factor in GaN-based SMPS design. Transistors controlling switching signals inherently generate EMI, which can be a major concern depending on the application and industry standards. Detecting and addressing EMI issues early in the design process is vital to avoid costly EMI validation tests and ensure compliance with increasingly stringent EMI and Electromagnetic Compatibility (EMC) regulations.
• Efficient thermal management: Modern power supplies are particularly sensitive to heat generated in semiconductor switches. Higher temperatures lead to increased losses and reduced efficiency in these components. Traditionally, SMPS design engineers relied on manual calculations using complex mathematical equations and spreadsheets, a time-consuming and error-prone approach. This method often overlooked critical factors like airflow patterns and ambient temperature, resulting in less accurate thermal estimates.
• Comprehensive power module design and simulation: Power modules have become ubiquitous in various applications, including electric vehicles, high-speed trains, and renewable energy systems. These modules handle a wide range of power levels and high currents, often utilising multiple parallel power transistors. Effective power module design necessitates careful consideration of layout effects, such as current balancing among branches and switching losses, to ensure optimal performance and reliability.

The integration of GaN into power electronics design presents a promising avenue for achieving higher efficiency, power density, and miniaturisation in various applications. However, this transition requires careful consideration of key factors such as accurate modelling, post-layout simulation, EMI mitigation, thermal management, and power module optimisation.

While GaN offers significant advantages, it also introduces complexities due to increased switching speeds and voltage spikes. Traditional design approaches often fall short in addressing these challenges, leading to costly prototyping, extended time-to-market, and limited testing capabilities.

By adopting a comprehensive and proactive design methodology that prioritises the aforementioned key considerations, engineers can overcome these obstacles and unlock the full potential of GaN in power electronics. This will not only drive innovation but also contribute to a more sustainable and efficient energy landscape.