By John Wilson, Senior Product Manager, Silicon Labs, and Philip Zuk, Senior Director of Technical Marketing, Transphorm
As the global energy mix transforms to adopt low-carbon energy sources and energy-efficient transportation, pressure mounts for energy efficient cars. Today, the overall Electric Vehicle (EV) market already outpaces the conventional Internal Combustion Engine (ICE) vehicle market growth rate by 10x. The EV market is estimated to own 35 percent share of new vehicle sales by 2040, a remarkable portion of new automotive sales for a market that started mass production less than 10 years ago.
Economics combined with innovations in battery, electronic systems, and system components have played a crucial role in EV growth as the overall automotive industry moves from mechanical-based systems to digital ones. EV manufacturers and designers are embracing digital designs, and Canaccord Genuity projects semiconductor content in EV solutions will increase by as much as 50 percent or more per vehicle by 2025. This paper will examine how galium nitride (GaN) electronics, and to a lesser extent silicon carbide (SiC), are boosting the power output and energy efficiency of electric cars without increasing the cost of the vehicles.
The EV category typically includes battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs). Hybrid electric vehicles (HEVs) may be included, though they have a larger reliance on an ICEs than the electric propulsion system. For the remainder of this discussion, HEVs will be included in the EV definition given the number of electronics required to develop such vehicles. EVs inspire the design and development of innovative electrical systems to replace historically mechanical systems, such as:
Logically, such systems require electronic components, including numerous semiconductor devices. Still more semiconductor sockets emerge due to advanced battery management techniques.
Systems like those listed above typically rely on low- and medium-voltage silicon (Si) MOSFETs (≤ 150V) in circuits powered by a 12V battery. The industry is presently replacing 12V batteries with higher voltage ones (24V and/or 48V) to accommodate the increased power demand without increasing wire size and wiring cost. This replacement process also reduces copper wire weight, improving the drive efficiency.
As of today, drive wheel electrification requires a car to also house a second, high voltage (HV) battery ranging from 250V to 450V along with supporting electronics. (Note: This battery is expected to move to a higher voltage in the future, which will call for newer, advanced electronics.)
Perhaps even more so than with ICE vehicles, every pound matters with respect to EVs. Too much weight and the longevity and quality of the consumer experience degrades.
And, as is true with any product, cost control (ideally, cost reduction) remains a priority. Even as new features are designed in, overall system costs must keep up with downward market pressure on price.
The introduction of all of these new systems greatly increases the number of semiconductors and other electronics as well as the battery power needed. In theory, this translates to more weight and more cost. As a general rule, the cost of a Si transistor switch scales higher with bus voltage increases—the opposite of what vehicle electrification demands. Additionally, performance requirements of some of the new in-vehicle systems call for impractical numbers of Si devices—thereby driving up weight and system size as well as price.
Essentially, the new EV systems are difficult to support with such incumbent semiconductor technologies like HV SiMOSFETs, IGBTs, and superjunction. Instead, the industry is turning toward powerful alternative wide bandgap (WBG) technologies, including silicon carbide (SiC) and gallium nitride-on-silicon (GaN-on-Si).
Both disruptive technologies have their place in EV electrification.
SiC offers higher blocking voltage, higher operating temperature (SiC-on-SiC) and higher switching speeds than Si IGBTs. These capabilities are optimal for traction inverters given their critical need to transfer large packets of energy back to the battery intermittently.
Meanwhile, GaN-on-Si switches provide benefits to a wide array of power systems ranging from the low kWs to 10kW (i.e., AC to DC on-board chargers (OBCs), DC to DC Auxiliary Power Modules (APMs), heating and cooling units, etc.).
|Semiconductor||Targeted Voltage||Cost||Application Examples|
|GaN (low-mediumvoltage)||30 V – 300V
||$||Systems driven by APM’s/LIDAR
|GaN (high voltage)
||650V – 900V||$$||
DC to DC Converters(APM’s)
|SiC||900 V to 1200V+
GaN’s attractiveness lies in several intrinsic attributes outperforming and outranking Si attributes. GaN offers lower switching loss; faster, RF-like switching speeds; increased power density; better thermal budgets; and, important to EVs in particular, overall system size, weight, and cost reduction. GaN also enables engineers to employ a system topology leveraging those attributes: the bridgeless totem-pole power factor correction (PFC). As a totem-pole PFC system’s power requirements increase, GaN’s benefits become increasingly more relevant.
Figure 1: Traditional boost CCM PFC versus GaN-enabled bridgeless totem-pole PFC
The automotive industry’s shift to vehicle electrification not only changes the type of technology used, but redefines the definition of an automotive supplier. Traditional Tier One suppliers started by manufacturing mechanical systems, not electrical systems. These companies have begun developing electrical systems per need, but the demand for smarter, more innovative electrification opens opportunities for untraditional suppliers.
In their simplest form, in-vehicle power conversion systems are basic AC to DC, DC to AC and DC to DC converters. These converters are widely used in numerous markets and applications today including power supplies, telecommunications, and off-board battery chargers. Supplying these systems to the automotive industry is an easy, logical market expansion for switch mode power supply (SMPS) original design manufacturers (ODMs) eager to fill a growing gap in the automotive market. In fact, this new sourcing concept is inevitable given that advanced electrical systems—particularly those using GaN—require extensive expertise developed over decades.
The automotive industry is highly regulated, often requiring sourced components to be the highest quality and reliability as proven by their ability to meet Automotive Electronics Council (AEC) industry standards. The SMPS and ODM will require a supplier network of advanced semiconductor devices and active components committed to meeting those standards.
Regarding GaN, AEC-qualified parts already exist for one of the more crucial electronic subsections: the power switching device and gate driver pairing.
Transphorm offers an automotive-grade AEC-Q101 qualified GaN FET—the 650V TPH3205WSBQA FET featuring an on-resistance of 49 mΩ in a TO-247 package. When compared to silicon technologies, these transistors deliver all of the primary GaN benefits: up to 4x faster switching speeds, reducing voltage and current cross-over losses; up to a 40% power density increase; and, overall system size, weight and cost reductions (metrics dependent on the application).
While Transphorm’s FETs can be paired with most off-the-shelf gate drivers, SMPS ODMs and Tier One suppliers can build systems by using Silicon Labs’ Si827x isolated half bridge gate drivers. These drivers are AEC-Q100 qualified and meet standard quality and documentation requirements for automotive semiconductor devices.
HV GaN power supplies are somewhat unique in the power supply industry: as noted, GaN devices switch at radio frequency speeds. Much faster than incumbent power electronics switching speeds. Given this, effective high-speed gate drivers with high common mode transient immunity (CMTI) are critical to optimizing the Transphorm GaN FET’s performance. To that end, the Si827x drivers have a CMTI spec of 200 kV/μs minimum—the highest CMTI spec available from an isolated driver.
The GaN material’s energy-saving properties and ability to handle high voltage operations without losing power gives designers critical advantages in designing tomorrow’s EV vehicles, including lower switching loss, faster switching speeds, increased power density, improved thermal budgets; and further weight and cost reduction. Even beyond theEV market, GaN-based electronics offers tremendous opportunity to further reduce power consumption in data centers and consumer devices.
Electric car designers have already delivered unprecented innovation since the market’s inception, and the future will bring more change and growth as the digitalization of cars continue. Tomorrow’s EV vehicles will be cooler, faster, and smaller, providing drivers (and autonomous drivers) with amazing performance gains while enabling more ground to be covered with less power and energy.