Whether SiC or GaN, they are only supplements to silicon materials rather than substitutes

With the growing number of mobile devices, laptops, and tablets, the demand for low-voltage power adapters has never been greater.

In fact, according to Dr. J. Christopher Dries, president and CEO of UnitedSiC, there are more than 300 million low-voltage chargers in use today, each of which contains a flyback converter.

Because these devices rely heavily on power conversion, designers have been working to improve efficiency and reduce conversion losses generated by traditional switching circuits.

Currently, the low-voltage charger market is still dominated by silicon materials and has been for decades.

"Silicon technology still dominates the market, and if we are to seriously improve efficiency, we need to reduce the heat losses of these devices." explained Aly Mashaly, power systems manager at ROHM Semiconductor Europe.

“It used to be that if you left your laptop on for a few hours it would get really hot, today we are seeing significant improvements due to the increased efficiency of electronic devices. However, as devices become more power hungry, there is also a need to improve the efficiency of low voltage adapters.”

“Currently, low voltage adapters are still mainly driven by MOSFETs,” said Dr. Dries. “This is an affordable solution because consumers don’t want to spend a lot of money on mobile phone chargers. But people also want to improve efficiency, especially in terms of size and weight.”

To help this process, UnitedSiC is developing a SiC product that it believes can compete with similar products and have a cost advantage.

“Many SiC companies are focused on the high power market, such as the 600V and above product market, such as car chargers,” Dr. Dries explained. “But we see an opportunity to bring SiC technology to the low power market. In fact, no one has done this before, and we allow people to spend a little more money but get significant performance improvements in terms of efficiency and frequency.”

Its SiC JFET chip can be co-packaged with the low voltage MOSFET and controller. Dr. Dries said this will create an extremely fast, cascode-based 20-100W flyback product that can significantly save space and have an efficient flyback power supply topology.

These normally-on SiC JFETs are available in a voltage range of 650V to 1700V, enabling simplified startup, zero standby power consumption, and are suitable for the flyback AC-DC application market, including consumer adapters.

According to Dr. Dries, the converter has very low RDSON and capacitance, which allows for a small size while meeting standby power consumption regulations at light load and no load.

SiC JFETs avoid avalanche and short circuit phenomena, so the entire system can be more robust. Since the SiC JFET is in series with the low-voltage MOSFET in the control IC, the source of the normally-on JFET rises to 12V before turning off when the IC starts switching, and the current path through the JFET can be used as the startup power supply for the controller IC. Then, when the converter starts running, the auxiliary power supply from the converter transformer is gated, with no further dissipation.

Some companies are looking to achieve the same effect with the wide-bandgap material of gallium nitride (GaN) because, like SiC, it offers higher frequencies and greater efficiency, enabling “more compact and better adapters”, according to Dr Dries. But so far only a few have been successful.

GaN v SiC

One of those companies is ROHM Semiconductor.

“We believe GaN is the technology to watch,” says Mashaly. “GaN is different from SiC because it conducts laterally, which means it is better suited for low-voltage applications. We believe that in low-voltage applications, GaN will be more efficient than either silicon or SiC.”

However, Mashaly acknowledges that GaN is not yet widely used in this area.

“As far as GaN is concerned, we have seen some efforts in size reduction and efficiency, but it is still early days for the market. The industry is talking a lot about GaN and there is growing interest in its benefits in the low voltage space. However, I don’t see silicon going away and all three technologies (silicon, SiC and GaN) will be competing simultaneously in 20 years.”

“It offers us huge cost and performance advantages while providing our customers with an additional feature set. The standard gate drivers we offer can be driven by existing silicon solutions, so customers who have silicon in their designs today can directly replace the power supply with our products and get higher efficiency,” explained Dr. Dries.

He continued, “If you compare our products to GaN, we have more die per wafer, so while SiC is more expensive than silicon and potentially more expensive per wafer than GaN, the higher number of die per wafer offsets that.” According to Mashaly

, “GaN is about 10 years behind the SiC industry, so the material cost has to come down. We have low voltage devices, such as diodes and silicon MOSFETs, and in the near future we will start to bring GaN devices into the low voltage space.”

“We are always looking for ways to reduce the cost of our devices by removing components that are not needed, such as not needing cooling fans, etc.” Mashaly believed. He continued, “This means that we can afford to use slightly more expensive products, such as GaN, and still end up with a lower total system cost than before.”

Dr. Dries acknowledged that the cost of SiC may be an issue, but he believes that the performance advantages outweigh the cost, and he hopes that in the near future, UnitedSiC will be selling for prices close to 650V silicon chips.

UnitedSiC announced a strategic investment from Analog Devices in March, “They are a great partner. I believe they will be the first of many analog IC companies that want to work with us,” commented Dr. Dries.

Whether it’s GaN or SiC, the motivation for semiconductor companies to turn to wide-bandgap materials isn’t to replace the traditional silicon industry.

“Rather, it’s for different use cases,” Mashaly said. “We’re looking for greener energy, higher efficiency, and that’s why we need to start exploring new materials.”