Since the birth of wide band gap (WBG) devices, it has brought an exciting wave to power conversion applications. But under what circumstances does it make sense to switch from silicon to wide band gap technology? So far, silicon-based power devices such as shielded gate MOSFETs, super junction devices, and IGBTs have been widely used in the industry. These devices continue to improve in terms of quality factor (FoM), coupled with advancements in topology and switching mechanisms, enabling engineers to achieve higher system efficiency. Perhaps the most common reason why engineers insist on continuing to use silicon wafers is their extensive knowledge and experience in this area. However, in some cases, the performance requirements of next-generation power supplies, inverters, and photovoltaic systems make WBG device applications the first choice.
In medium voltage applications, Infineon’s OptiMOS can provide the industry’s better quality factor. Applications that require 100-200V MOSFETs, such as switching power supplies (SMPS), inverters, and battery-powered motors, are already using these high-frequency optimization devices. However, as artificial intelligence (AI) coprocessors and other edge computing applications that require huge currents become more and more widely used, requirements are put forward for improving power supply efficiency and transient load response capabilities. CoolGaN can provide FoM and zero reverse recovery charge significantly better than any similar medium voltage silicon device, which makes it a perfect choice for half-bridge circuits. Due to its crystal plane growth characteristics, the package can realize the innovative mechanism of top heat dissipation. In a 54V input/12V output step-down converter, the CoolGaN-based design can provide 15A current and achieve a peak efficiency of over 96.5% at a switching frequency of 500 kHz. This is a 1% increase in efficiency over the equivalent OptiMOS 5 100V at a switching frequency of 100 kHz.
High-voltage applications in the 400-650V range will also benefit from CoolGaN devices. The efficiency improvement achieved by using higher switching frequencies can increase power density. This feature is becoming more and more valuable in space and weight. Communication and server power supplies Is particularly important. A complex Pareto analysis of 3kW/12V power supply shows that CoolGaN technology can provide 0.7% higher efficiency than super junction CoolMOS devices at a power density of approximately 67W/in3. One thing to note here is that the first-generation GaN devices are currently at the beginning of their technology roadmap. Studies have shown that in terms of on-state resistance per unit area, we are still an order of magnitude away from its theoretical limit.
TRENCHSTOP IGBT has long been the main force for applications requiring 1200V switching, and has become an important product for applications such as photovoltaic inverters, SMPS and automotive inverters. Like MOSFETs, each new generation of devices further improves the trade-off between VCEsat. However, with the emergence of silicon carbide (SiC) technology, solid trench MOSFETs such as CoolSiC have obvious advantages in conduction and switching losses, and are quickly gaining acceptance in the above-mentioned applications. The hard-switching totem pole power factor correction circuit (CCM PFC) is an example. CoolSiC can usually operate at a temperature of about 100°C, and the relatively flat RDS(on) with temperature changes means that a 94mΩ device can achieve 99% efficiency in a 3.3kW CCM totem pole PFC.
In general, CoolGaN and CoolSiC can provide better FoM, and can achieve higher efficiency than similar silicon devices. However, these are not the only factors that need to be considered. Price is also very important, as are the risks associated with the adoption of new technologies. Both GaN and SiC have different driving and operating characteristics. In order to fully realize the potential of these technologies, new topological architectures or control technologies may be needed.
For totem pole PFC in applications such as servers, both SiC and GaN devices can be used. Since the RDS(on) temperature dependence of SiC devices is very low, it can be used first for CCM control, while GaN has advantages in resonant totem pole applications. In traditional boost PFC, silicon MOSFETs can achieve ideal system efficiency at a lower cost than WBG devices, so silicon MOSFETs are still the best choice. When power density is very important, especially under light load conditions, CoolGaN has lower gate drive loss, making it a better choice, while CoolSiC is the second best choice for high-frequency applications in servers and telecommunications. This is especially true for LLC design. In the field of automotive applications, we expect that applications such as on-board chargers, DC-DC converters, and main inverters will increasingly demand SiC MOSFETs.
Designers like more options to make the best design. In order to meet these needs, Infineon is developing a variety of WBG devices to supplement its industry-leading silicon technology, allowing system designers to retain certain silicon technologies while maintaining certain silicon technologies. Can improve product design. However, when the time is right, the WBG solution will be able to push the power supply design to unprecedented high efficiency and high power density.
