Which power supplies are recruited by Gate 2019

How GaN semiconductors reduce the size, weight and costs of electric cars

The EV (Electric Vehicle) category typically includes battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs); in the following this article also includes hybrid electric vehicles (HEVs). EVs inspire the design and development of other electrical systems to replace previous mechanical systems. These include, for example, air conditioning units (transition to compressors with BLDC or three-phase motors), vacuum and pneumatic controls (transition to electronic control modules), drive-by-wire systems (transition to electromechanical actuators), parking brakes (transition to electrically operated Brake calipers) and drive wheel systems (transition to end-to-end electrification). The semiconductor content per vehicle is to increase by at least 50 percent by 2025.

As a result, such systems require electronic components, including numerous semiconductors. The use of suitable battery management techniques also entails additional semiconductor areas.

Systems require more energy

The vehicle systems are usually based on circuits with low and medium voltage silicon MOSFETs (≤150 V), fed by a 12 V battery. The industry is currently replacing 12 V batteries with higher voltage batteries (24 and / or 48 V) to meet increased energy demands without increasing cable size and wiring costs. On the one hand, this results in a reduction in the weight of the copper wire and, on the other hand, an improvement in the efficiency of the drive.

Image 1: The nationwide power supply for electric vehicles is to be expanded further in the future. Silicon Labs

As a result of the electrification of the drive wheel, a car currently has to accommodate a second high-voltage battery with a voltage of 250 to 450 V and supporting electronics. In the future, this battery could be converted to a higher voltage, provided that the necessary electronics are available. The nationwide power supply for electric vehicles also needs to be improved in the short to medium term (Fig. 1).

Electrification leads to "GaN-ification"

Perhaps even more than in vehicles with a combustion engine, every gram counts for EVs in order to achieve the highest possible efficiency. Control of costs also plays an important role so that the overall system costs can keep pace with the price pressures of the market, even after the integration of additional features.

Essentially, the new EV systems with established semiconductors such as HV-Si-MOSFETs, IGBTs and SJ components (superjunction) are difficult to support. Instead, the industry is turning to wide-bandgap technologies: silicon carbide (SiC) and gallium nitride on silicon (GaN-on-Si).

Both disruptive technologies have their place in EV electrification. SiC offers a higher reverse voltage, a higher operating temperature (SiC-on-SiC) and higher switching speeds than Si-IGBTs and is therefore suitable for traction inverters.

Table 1: Overview of different semiconductor types with regard to target voltage, costs and possible applications. Silicon Labs

GaN-on-Si switches are now beneficial for a wide range of power systems ranging from a few kW to 10 kW, such as built-in AC / DC chargers (OBCs), DC / DC auxiliary power supply modules (APMs), or heating - and cooling devices (Table 1). Compared to Si, GaN offers lower switching losses; faster, RF-like switching speeds, higher power densities, better heat budgets and - especially important for EVs: a reduction in overall system size, weight and costs.

Figure 2: GaN uses a system topology with a bridgeless totem pole PFC, in contrast to a conventional boost CCM PFC. Silicon Labbs

In addition, with GaN, engineers can also use a system topology (Figure 2) that takes advantage of these properties, namely bridgeless totem pole power factor correction (PFC). As the power requirement increases, the advantages inherent in GaN become more apparent here.

Further development in procurement and qualification

The transition of the automotive industry to vehicle electrification not only changes the type of technology used, but also redefines the description of an automotive supplier. So far, tier 1 suppliers have mainly manufactured mechanical systems. You have started developing electrical systems as needed, but the demand for higher intelligence and innovation opens up opportunities for unconventional providers.

The automotive industry must meet the standards set by the Automotive Electronics Council (AEC). Switching power supply ODMs need a network of suppliers of suitable semiconductor modules and active components that is committed to complying with these standards. AEC-qualified GaN components currently exist for the most important sub-areas: the power switching device and the gate driver pairing.

Transphorm offers an AEC-Q101-qualified GaN-FET, the TPH3205WSBQA-FET for 650 V with an on-resistance of 49 mΩ in a TO-247 package. Compared to Si technologies, these transistors guarantee all of the primary GaN advantages: up to four times faster switching speeds, which reduces losses at voltage and current transitions, and up to 40 percent higher power density. They also reduce the overall system size, weight and costs (depending on the application).

While FETs from Transphorm can be combined with most commercially available gate drivers, SMPS-ODMs and Tier 1 systems can work with the isolated half-bridge gate drivers Si827x from Silicon Labs. These drivers are AEC-Q100 qualified and meet the standard requirements for quality and documentation for semiconductors in the automotive industry.

HV GaN power supplies are currently in use in the power supply industry: Because GaN devices switch at RF speed, high-speed gate drivers with high common mode transient rejection (CMTI) are crucial for optimizing the performance of the Transphorm GaN FET. For this purpose, the Si827x drivers have a CMTI specification of at least 200 kV / µs - the highest currently available for isolated drivers.

A look into the future

Whether innovation, transformation, evolution or revolution: The EV movement is turning an established industry on its head that has hardly seen any substantial changes in more than three quarters of a century. From redesigning consumer experiences to completely redesigning the internal support systems, from recruiting new suppliers to increasingly focusing the energy supply on quality and reliability - these shifts are driving EV acceptance further. Should it be possible to make electrification more cost-effective in the future while at the same time experience with system design grows, this could be the starting signal for a wave of many new innovations.

(aok)