When selecting high-power switching devices for power conversion, there were only two choices in the past, silicon MOSFETs or IGBTs, but the latest applications such as AC-DC converters, inverters, DC-DC converters, etc., have reached thousands. At the V level, it is necessary to consider products such as SiC that are more resistant to high pressure. For high-voltage switches, SiC MOSFETs offer significant advantages over traditional silicon MOSFETs and IGBTs, supporting high-voltage rails over 1,000 V, operating at hundreds of KHz, and even surpassing the best silicon MOSFETs.
It is worth noting that SiC devices can meet new requirements, but their circuit requirements are different. Specifically, they have special gate drive requirements, and ON Semiconductor has solved this problem with its SiC gate driver family, bringing the benefits of SiC MOSFETs to today’s demanding power supplies, especially automotive electrical systems and Electric cars, etc.
SIC Application target
SiC transistors are suitable for almost any switch mode power supply. Their superior characteristics make them more obvious in automotive electrical systems, such as AC-DC power supplies with power factor correction (PFC), DC-DC converters, and car chargers (OBC). ), inverters, LiDAR and circuits for all-electric or self-driving vehicles.
Some non-automotive applications include motor drives, photovoltaic (PV) inverters, PV chargers, uninterruptible power supplies (UPS), and network and server power supplies. All of these applications benefit from the increased efficiency of SiC design.
Power design engineers have realized that SiC transistors are indeed the best choice for new switch mode designs, and while they may be a bit more expensive than alternatives, they offer even more advantages. The following are the advantages of SiC compared to MOSFETs and IGBTs:
- High withstand voltage. Most SiC devices are capable of handling voltages from 650 to 1700 V, and they can replace some IGBTs in high voltage applications.
- High current capability with versions over 100 A.
- Switching faster and at speeds up to 1 MHz.
- Ultra low on-resistance up to hundreds of milliohms.
- Better thermal conductivity means that the temperature rise is minimal for a given power dissipation.
- Lower turn-off losses, lower conduction losses and lower gate charge.
- Smaller physical size.
- AEC-Q101 compliant automotive grade certification.
SIC Typical Equipment
The ON Semiconductor SiC MOSFET is ON Semiconductor’s NTHl080N120SC1 (Figure 1).
ON Semiconductor’s SiC FETs are available in a TO-247 package. The main features include:
- The maximum drain voltage is 1200 V.
- The maximum continuous current is 31 to 44 A, depending on the ambient temperature.
- Typical on-resistance “110mΩ.
- Recommended gate – source voltage is -5 to +20 V.
- Power consumption is 58 to 348 W, depending on the ambient temperature.
- TO-247 packaging.
Designed with SiC
Design using SiC transistors is different from design using conventional silicon MOSFETs and IGBTs. The main difference is related to the requirements of the door drive. When using a standard enhanced MOSFET, you can rest assured that the MOSFET is fully turned on when the gate threshold voltage (VTH) is exceeded. VTH ranges from a few volts to a maximum of about 10V.
For driving SiC MOSFETs, the gate-to-source threshold VTH must be in the range of 20 V to ensure a good current path between the source and drain. But that’s not all. To turn off the device, a negative voltage of -3 to -10 V is required on the gate. In the early days, SiC’s drive design was paired with discrete components and has now become an integrated IC.
ON Semiconductor’s NCP51705 is a universal driver IC that can be paired with ON Semiconductor or other brands of SiC devices that provide separate output stages for independent on and off regulation. Source and sink capability is 6 A.
The NCP51705 also provides a 5V power rail that can be used to power external circuits such as opto-isolators. The IC’s protection features include biased undervoltage lockout monitoring and thermal shutdown based on the driver junction temperature.
Car design example
Electric vehicles (EVs) and hybrid vehicles (HEVs) require OBCs for high voltage AC to DC and auxiliary batteries. Figure 2 shows a simplified diagram of such a system. The standard bridge rectifier converts AC power to DC voltage and is power factor corrected. The full-bridge DC-DC converter provides an input to the resonant flyback converter that regulates the voltage to a higher level and rectifies it to the final DC charge that charges the main battery. Current battery voltages range from 300 to 900V, and separate circuits generate low voltage (12 V or 48 V) for battery charging for all other electrical and electronic components, such as vehicle lighting and infotainment.
The DC-AC inverter in the EV that drives the main vehicle motor is also an application area for SiC. IGBTs are now used in many designs and can also be replaced with SiC devices.
IGBTs used in EV motor drive inverters can now be replaced with SiC MOSFETs.
PFC and DC-DC converters are the primary targets for SiC applications because of their high voltage, high current and high speed switching capability.
As a conclusion, in addition to voltage, current and switching speed advantages, SiC devices can operate at high temperatures and are extremely rugged with low turn-on and switching losses. High thermal conductivity also makes SiC an ideal choice for high power applications with good heat dissipation. In this regard, ON Semiconductor’s SiC MOSFETs offer high efficiency, higher power density and smaller system size.