Automotive Applications of GaN Power Semiconductors

EV charging is one of many use-cases for GaN technology

The automotive industry is undergoing the biggest change in its history, as it shifts from internal combustion engines (ICE) to electric power. While the electric powertrain is a well-proven technology by now, there’s continued pressure to achieve greater range and faster battery changing – raising the bar of what’s expected of power electronics components.

Silicon is the incumbent semiconductor material for power applications, but in our cars, it’s being replaced by wide bandgap (WBG) materials that offer improved efficiency and greater power density.

The two most commonly used WBG materials are gallium nitride (GaN) and silicon carbide (SiC). Although it offers excellent performance, GaN is typically only suited for applications up to around 650 V. 

Where higher voltages are needed, such as in a typical traction inverter, then silicon or SiC is often more suitable, although the technical limits of GaN continue to expand as new devices are developed.

For these low and medium voltage applications, GaN offers higher efficiency compared to silicon. This is due to multiple factors, including GaN devices’ higher switching frequencies, its zero reverse recovery losses, and its lower drain to source on-state resistance (R_DS(on)) than silicon, which reduces conduction losses.

In power applications, the most common GaN device is the lateral high electron mobility transistor (HEMT). In this article, we will explore some of the most common automotive applications for GaN HEMTs and field-effect transistors (FETs), and why GaN’s advantages make it a preferred choice – specifically, its excellent efficiency and high power density.

GaN applications in electric vehicles

In an electric vehicle (EV), GaN is typically found in the onboard charger (OBC), which converts AC power from the grid into DC that can charge the battery. This is for charging from a standard or low-power AC outlet, for example plugging into a regular socket at your home. An OBC is typically rated between about 1.2 kW and 7 kW for single-phase versions, and up to around 22kW for less common three-phase options.

GaN devices can also be used in EV fast charging systems within rapid, high-voltage DC charging stations often found in public locations. These can deliver power up to around 100 kW in a typical installation, enabling an EV to charge its battery from 10% to 80% in something like 30 minutes¹. So-called ‘ultra-rapid’ chargers can go even faster, with power ratings of up to 350 kW and charging from 10% to 80% in 20 minutes or less, depending on the car’s capabilities.

Another application is the EV’s on board DC/DC converter, where GaN’s efficiency and high power density are key. For all these automotive applications, GaN-based devices also need to deliver excellent reliability, and to meet the stringent requirements of automotive quality standards such as AEC-Q101.

While the discussion in this article is focused on EVs that only contain an electric powertrain, with no conventional diesel or petrol engine, the same principles also apply to hybrid vehicles, including mild hybrids, conventional hybrids (HEVs), and plug-in hybrids (PHEVs).

GaN semiconductors in OBC design and V2G

Let's take a closer look at one specific application: the onboard charger (OBC). This device is crucial for converting AC power from the grid into DC to charge the EV's battery. OBCs can be designed as unidirectional, for charging only, or bidirectional, which allows for vehicle-to-grid (V2G) capabilities, enabling the car to feed power back to the grid.

An example of a high-efficiency OBC design is shown in Figure 1, consisting of a ‘Totem-Pole’ PFC stage, followed by an isolated ‘CLLC’ DC-DC conversion stage².