A Wave of SiC MOSFET Designs Power Up to Strike at High Voltage Applications
As industrial power electronics move towards higher operating frequencies and voltage, silicon carbide (SiC) technologies are emerging to meet the demands of next-generation power electronics.
Silicon (Si) MOSFETs (metal-oxide-semiconductor field-effect transistors) are widely used in almost every electronic circuit, and silicon has been the semiconductor material for transistors.
However, in recent years, SiC has been a contender to replace silicon as a standard semiconductor material in the field of power electronics.
Overview of Si vs. SiC parameters. Image used courtesy of IOP
In this article, let's discuss the differences between Si and SiC in MOSFETs, specifically, and then dive into new products from Power Integrations, Microchip, and STMicroelectronics (ST).
SiC vs Si MOSFETs
With emerging technologies, such as fast electric vehicle (EV) chargers, powertrains, and smart grids, there is a need for switching devices that operate at higher frequencies and can switch efficiently.
This need is where SiC MOSFETs come into the picture, as Si MOSFETs are reaching their operation limits.
All in all, SiC MOSFETs tend to have a lower drift layer (a layer introduced between two heavily doped p or n-layers) but a higher channel resistance, which means that a high gate-source voltage will lower the on-resistance.
Moreover, the gate resistance of a SiC MOSFET depends on the sheet resistance of the gate material and the chip size. As the chip size of a SiC MOSFET is small compared to a silicon device, the gate capacitance of SiC MOSFETs is usually small, which is good for operation at high frequencies, but the internal gate resistance is high.
While high gate resistance negatively impacts the operability at high frequencies, it provides surge protection, making SiC MOSFETs reliable.
Despite some of the drawbacks, there are still more advantages to using SiC for MOSFETs.
Advantages of SiC MOSFETs
In general, SiC devices have a plethora of different advantages over Si.
SiC MOSFETs can operate at higher temperatures, have a higher operating frequency, exhibit low ON-resistance, provide high current density, and present reduced switching losses than Si MOSFETs.
As a fact, wide-bandgap semiconductor devices can switch 100 to 1000 times faster than their silicon counterparts.
As for efficiency, SiC-based solar inverters can achieve efficiency up to 86.5%, and losses get reduced from 13% to 16%. Furthermore, they can operate at a higher voltage range and are thermally stable than Si MOSFETs.
Due to these numerous advantages, SiC MOSFETs are popular in applications like:
- Photovoltaic inverters
- Motor drives
- EV charging
- Smart grids
To address the requirements of such applications, semiconductor companies are developing state-of-the-art SiC solutions, speeding up system development.
"Industry First" High-switcher IC SiC MOSFET
These ICs are based on 1700 V SiC MOSFETs on its automotive-qualified InnoSwitch3-AQ family. The new devices claim to be the "industry's first" automotive-qualified switcher ICs to integrate SiC primary switching MOSFET.
The devices are targeted for 600 V and 800 V applications and deliver an output power of 70
Power supply reference design based on InnoSwitch3-AQ 1700 V switcher IC. Image used courtesy of Power Integrations
The InnoSwitch IC family aims to significantly reduce the number of external components required for implementing a power supply and simplifies system development by reducing component selection challenges. Moreover, it can operate from any voltage between 30 V to 1000 V.
The new ICs incorporate FluxLink technology to provide reinforced isolation up to 5000 VRMS for secondary-side control and direct output voltage sensing for fast transient response and accurate regulation.
They include synchronous rectification and a quasi-resonant (QR) / CCM flyback controller, which provides more than 90% efficiency. The new devices consume less than 15 mW at no-load, making them highly suitable for a wide range of industrial power applications.
Microchip Leverages SiC Capabilities for New Designs
Mersen Power Stack reference kit. Image used courtesy of Mersen and Microchip
Mersen's reference design claims to help system designers with SiC solutions without the need for device selection, testing, and qualification.
Additionally, it provides 16 kW per liter power density and up to 98% efficiency, with up to 20 kHz switching frequency. The reference designs are available in 700 V and 1200 V options, with a current handling capacity of 750 A.
The reference design kit consists of Microchip's 1200 V MSCSM120AM042CD3AG SiC MOSFET and AgileSwitch 2ASC-12A1HP digital gate driver. The kits are predesigned for inverter applications, enabling rapid prototyping and reducing time to market.
ST's Gate Drivers Simplify SiC-based Power Circuits
The final announcement rounding out this article is STMicroelectronics' two new dual-gate drivers, STGAP2HD for IGBTs and STGAP2SICD for SiC MOSFETs, hoping to ease circuit design in high voltage applications.
ST's STGAP2SiCD block diagram. Screenshot used courtesy of STMicroelectronics [Datasheet Download]
The new gate drivers incorporate ST's latest galvanic-isolation technology to provide transient voltage immunity.
The drivers also feature 100 V/ns transient immunity to prevent spurious turn-on in noisy environments, rated for up to 1200 V, claim to deliver a gate control signal of up to 4 A, and specify an input-output propagation time of 75 ns with high PWM (pulse width modulation) accuracy.
The new galvanically isolated gate drivers integrate numerous circuit protection features, including:
- Thermal protection
- A watchdog
- Under-voltage lockout (UVLO) per channel
- Interlocking to prevent shoot-through currents
- An iLOCK pin to turn on two channels simultaneously in dual low-side and half-bridge applications
Thus, with all these features integrated into a single chip, ST's new gate drivers aim to simplify high voltage circuit design.
Moreover, the input pins of gate drivers are TTL and CMOS logic down to 3.3 V compatible, simplifying the interface to a microcontroller or a signal processor.
Future Perspectives of SiC Technology
Overall, power electronics play an essential role in developing increasingly efficient applications like EVs.
As silicon devices exhibit some critical limitations, wide-bandgap semiconductors aim to replace Si devices in high voltage and high-frequency applications.
A new range of more efficient gate drivers and SiC MOSFETs are helping designers to replace Si MOSFETs in power circuits. SiC technology is set to further refine in terms of performance and production to meet the demanding requirements of next-generation high voltage power systems.