■ WBG, Increased Developer Adoption for Higher Switching Frequency and Power Density

Silicon power devices such as MOSFETs and IGBTs have proven to operate reliably in power applications over a long period of time. Their low price point and wide range of products on the market provide designers with a wide range of choices. It is also a familiar technology that power engineers have accumulated a lot of experience using for a long time.

So silicon devices are widely used for various purposes, but recently, design engineers are increasingly turning to wide bandgap (WBG) devices such as SiC or GaN. Wide bandgap devices can operate at higher switching frequencies than silicon, achieve higher efficiency, and enable higher power density. Therefore, the size and weight of power supplies can be reduced. Alternatively, the output power can be increased for a given form factor.

Figure 1 shows applications suitable for using Si, SiC, and GaN devices in power supplies.

■ Cost and efficiency

WBG devices are more expensive to purchase than silicon devices, but they achieve higher efficiency, which reduces power consumption and minimizes cooling needs, thus saving costs over their lifetime. Another benefit is that they reduce shipping costs by reducing the size of the power supply.

Therefore, it is important to carefully consider whether the total cost of ownership (TCO) savings from using WBG devices for your target application sufficiently offsets the higher initial purchase price of silicon devices. This calculation will vary for each use case. This is because things like required voltage, available space for power supplies, and cooling requirements will all be different.

For example, in a data center, power efficiency can be improved to reduce electricity usage and cooling requirements. This cost is a significant portion of the overall operating cost. In fact, one customer improved power efficiency from 97 percent to 97.8 percent by switching from silicon to WBG. This means that it takes about three years to offset the initial higher purchase price, but the power supplies have a lifespan of six to seven years. Therefore, it can be clearly seen that switching to WBG is more beneficial.

■ Real-world examples of wide band gap applications
○ Extremely compact 240W charger

Figure 2 shows a practical application example: an extremely compact charger providing two USB ports for portable consumer devices.

Recently, the EU has tightened environmental regulations to reduce electronic waste, requiring the use of universal USB-C chargers for consumer devices. These chargers must provide enough power to charge multiple devices simultaneously. It must provide an output voltage ranging from 5 V to the maximum voltage defined by the USB-PD specification, 48 V. In addition, it must be able to operate using different AC mains power sources around the world, ranging from 90 VRMS to 265 VRMS.

The USB-C cable is rated at 5A, so a universal charger with a maximum output voltage of 48V should be able to provide up to 240W. This is significantly higher than the 65W output power that USB chargers can provide today.

To achieve this, thermal management of the converter design is important, since only passive convection radiation and convection can be used to dissipate heat. Since WBG devices enable higher power densities and therefore smaller converter sizes, it is important to ensure that the surface temperature does not exceed the maximum temperature, which is typically specified as 70 C.

To meet these requirements, a three-stage approach to converter design is required to handle a wide input and output voltage range. Very high switching frequencies must be used to minimize the size of passive components and thereby achieve a compact design.

Looking at the charger design in Figure 3, the PFC stage consists of two interleaved totem pole stages, the DCX stage (DC transformer) operates continuously at the resonant frequency, and the DC/DC stage consists of two buck stages.

This design features Infineon's CoolGaN™ GIT (gate injection transistor) technology.w.infineon.com/cms/kr/wide-bandgap-semiconductors-sic-gan?utm_source=e4ds&utm_medium=referral&utm_campaign=202301_ap_kr_pss_pss.ppwbg_p&utm_content=e4ds+media-jan-mar&utm_term=tech+articles+series-wbg" target="_blank">CoolGaN™ IPS (integrated power stage) is used. CoolGaN GIT applies p-GaN gate to hybrid drain HEMT. GIT HEMT is used in half-bridge configuration, matching drivers are used for all HV sockets, and CoolGaN™ Schottky gate (SG) HEMT 100 V is used for buck stage.

The entire system can deliver the required 240W from each of the two USB-C outputs, achieving an outstanding power density of 42W/inch3. This is significantly higher than the 16W/inch3 to 20W/inch3 achievable with typical mobile phone chargers today.

■ Data Center Power Supply

Another important application, as mentioned earlier, is data center power supplies . The demand for data center processing capacity is rapidly increasing worldwide due to things like cloud services, artificial intelligence (AI), and cryptocurrencies. As a result, data centers are investing in high-efficiency power supplies to reduce server power consumption and cut costs.

Typically, high-efficiency power supplies for servers consist of a bridgeless PFC stage, such as a totem-pole stage, and a resonant DC-DC stage, such as an LLC converter. Center-tapped transformers are commonly used for 12 V output systems, while full-bridge rectification is a good choice for 48 V output.

Figure 4 shows the efficiency and power density of different server power supplies that deliver 7 kW at 54 V output. The all-GaN design achieves the best results in both efficiency and power density.

○ Extremely compact high-power DC-DC server power supply

Figure 5 shows another power supply module for data centers. With a single board size of 89.5mm x 66.0mm x 13.5mm, it delivers 1.5kW and achieves a power density of more than 300W/inch3. Efficiency is 92.3 percent at 10 percent load and 96.7 percent at 50 percent load.

In fact, what you see in Figure 5 is two modules combined in an IPOP (input-parallel output-parallel) configuration and sharing a single transformer core. In this configuration, these modules deliver 3kW output power with 250A output current at 12V, achieving a power density of 345W/inch3.

The snake core transformer used in this module enables ideal current sharing between phases and modules, and reduces core losses by having two modules share the transformer core with a single flux path.

■ WBG benefits should be carefully considered in terms of total maintenance costs

Today's power supply applications require extremely high efficiency and power density over wide input and output voltage ranges.

WBG semiconductors such as GaN and SiC initially cost more than silicon devices, but their lower power consumption and compact size help reduce total system cost over their lifetime.

Therefore, as we have seen in this article, the advantages of WBG devices should be carefully considered not only from a technical perspective but also from a total maintenance cost perspective.

Visit Infineon's WBG technology page to learn more about Infineon's complete portfolio of wide bandgap products and solutions designed to meet the efficiency and power density requirements of advanced high-power applications.

※ author
Dr. Gerald Deboy, Distinguished Engineer, Infineon Technologies