Why choose SiC?
To prove that your choice of SiC as the preferred power semiconductor for switch mode design is correct, please consider the following prominent features. Compared to standard or super junction MOSFETs or even IGBTs, SiC devices can operate at higher voltages, frequencies, and temperatures. Most of the power loss of other devices does not exist in SiC devices, so the efficiency of SiC devices can reach over 90% in most applications. Initially, SiC devices were more expensive than other MOSFETs or IGBTs. Nowadays, the price of SiC devices has significantly decreased, making it an attractive alternative solution.
Comparison between SiC and GaN
SiC and GaN devices both belong to the wide bandgap (WBG) category of devices, which are steadily replacing standard Si MOSFETs. They can operate at higher frequencies, making GaN devices more widely used in RF power applications. SiC devices are generally capable of withstanding higher voltages, currents, and powers than GaN devices. SiC devices have faster switching speeds and higher efficiency, making them suitable for switch mode power supply applications. In addition, SiC MOSFET contains a bulk diode.
Performance Considerations
An important characteristic of SiC is that its thermal conductivity is more than three times that of Si or GaN. Products based on SiC can operate at much higher temperatures (+175 ° C), while the conduction loss remains relatively stable throughout the entire temperature range. Another performance factor is that RDSon is extremely low, approximately 15 m Ω or less; Even at high operating voltages, it can achieve this specification level. This greatly reduces power loss, thereby improving efficiency.
The following important tips can help you create SiC semiconductor based switching power supplies when designing new power electronics products, providing higher power at a smaller size and lower cost.
01 Topology selection
In addition to standard half bridge and full bridge circuits, there are two other topologies widely used in SiC devices. These two topologies are bidirectional converters and Vienna rectifiers. The bidirectional architecture is essentially a buck boost type DC-DC converter that can be configured to provide two different voltage buses and exchange power as needed. This architecture is very suitable for vehicles with two battery buses, and all electric and mild hybrid vehicles have two battery buses. Ideally, these two buses can charge each other. There are currently commercially available ICs for implementing bidirectional converters.
Another topology is the Vienna rectifier, which is increasingly being adopted in designs. It is a three-phase, three-level PWM controlled bridge rectifier. Its main application is power factor correction (PFC) in high-power AC to DC power supplies.
02 Determine voltage and current requirements
In over 90% of current applications, SiC devices can replace IGBT. Nowadays, few new designs adopt IGBT. IGBT can withstand high voltages up to approximately 1900 V, but its switching speed is slow. SiC devices can cope with high voltage and current levels, but the switching speed is much faster. The upper limit of voltage that SiC transistors can withstand is 1800 V, making them a good replacement for IGBT. SiC not only has a higher switching frequency to improve performance and efficiency, but also allows for the use of smaller packages.
03 Attention Gate Driver
Compared to other MOSFETs, SiC transistors require a larger gate driving voltage. A typical SiC transistor requires a gate voltage of 15 V to 20 V to conduct and -3 V to -5 V to turn off the device. However, most SiC suppliers have already addressed this requirement through special gate driver ICs, making it easy to design using SiC devices.
04 Use modules as much as possible
The module is a complete pre wired MOSFET circuit, with optimized packaging for size and thermal performance. For example, a three-phase bridge module used to drive three-phase motors. It connects to other architectures to create DC-DC converters or three-phase rectifiers. The module integrates SiC MOSFET and SiC diode to ensure low conduction and switching losses. This architecture achieves high efficiency and excellent reliability in power products.
The module includes a temperature sensor (such as a thermistor) to monitor heat levels and provide some type of circuit protection or temperature control. Modules can significantly shorten design time and achieve smaller packaging. The ideal goal of the new design is to use 90% modules and 10% other discrete components.
05 Find reliable suppliers
When using complex devices such as SiC transistors and circuits, having a supplier who can not only supply products but also provide design solutions, information, and assistance can be beneficial.