How to unlock the potential of SiC MOSFETs in power electronic systems

Silicon carbide (SiC) MOSFETs offer numerous benefits over traditional silicon-based transistors in high-power electronic systems. The superior performance characteristics make them ideal for a wide range of applications, from electric vehicles (EVs) to solar photovoltaic (PV) arrays, motor drives, battery energy storage systems (BESS), and industrial automation and Industry 4.0 equipment, as shown in Figure 1. 

When specifying SiC MOSFETs, it is important to understand the parameters that influence the performance. These parameters are explained in reference to the NSF040120L4A0, a state-of-the-art 1,200 V SiC MOSFET from Nexperia.

Fig. 1: SiC MOSFETs offer efficiency and thermal management advantages in various applications

Understanding essential parameters specified in the datasheet 

When designing a power electronic system, it is crucial to understand the datasheet parameters of SiC MOSFETs, as the specifications directly impact power losses, system efficiency, and junction temperature. 

The key parameters are:

1. On-resistance: this influences conduction losses. A lower on-resistance means higher efficiency. But on-resistance increases with temperature. This also varies with gate-source voltage and drain current.
2. Total gate charge: the total charge required to switch the MOSFET from the off to the on state. This affects both power consumption in the gate-drive circuit, and delay time.
3. Gate-charge ratio: important for switching stability and mitigating Miller turn-on effects.
4. Threshold voltage: the gate voltage at which the MOSFET begins to conduct. This affects delay time and safety margins.
5. Switching energy: this determines the switching losses during transitions between the on and off states. Lower switching energy results in higher efficiency.
6. Thermal resistance and thermal impedance: these affect the thermal management of the SiC MOSFET, which is important for maintaining performance and longevity.

Conduction performance

On-resistance is the crucial parameter which affects conduction losses. The designer needs to take into account the degree of drift in the on-resistance value as junction temperature increases. 

For the NSF040120L4A0 SiC MOSFET, Nexperia provides detailed graphs in the datasheet which show how on-resistance varies with both temperature and current. An understanding of these variations helps engineers to optimize designs for different operating conditions.

Switching performance

Switching performance, governed by parameters including the gate-source threshold voltage, total gate charge, gate-charge ratio, and switching energy, determines the suitability of a SiC MOSFET for applications that require fast and efficient switching. The turn-on and turn-off processes of a SiC MOSFET involve complex interactions between these parameters. 

For instance, during turn-on, the gate-source capacitor charges until the threshold voltage is reached, initiating current flow and commutation.

Thermal management

Thermal performance, expressed in the thermal resistance and thermal impedance parameters, is of crucial importance in high-power applications. SiC MOSFETs cycle between on and off states, causing periodic heating and cooling. Designers must consider the average junction temperature, and the ripple effect caused by the duty cycle and pulse frequency. Accurate thermal modeling ensures reliable operation within safe temperature boundaries.

Practical application example

A bidirectional buck converter example illustrates the application of these parameters as shown in Figure 2. By iterating through calculations of power losses and junction temperatures, engineers can estimate the steady-state performance of the NSF040120L4A0 in real-world applications.

Fig. 2: A bidirectional buck converter based on the use of NSF040120L4A0 SiC MOSFET from Nexperia

SiC MOSFETs in Industry 4.0 and industrial automation equipment

The advent of Industry 4.0, characterized by the integration of smart technologies and automation in manufacturing processes, demands highly efficient and reliable power electronics. The use of SiC MOSFETs helps to meet these demands due to the superior thermal conductivity, high switching speeds, and reduced power losses. These characteristics make the SiC MOSFETs suitable for use in industrial robots, automated production lines, and smart grid applications.

In industrial automation, precision and efficiency are very important: SiC MOSFETs enable the development of more compact and energy-efficient motor drives. In addition, the robustness of SiC MOSFETs ensures long-term reliability, reducing maintenance costs and downtime in industrial settings.

Conclusion

SiC MOSFETs such as the Nexperia NSF040120L4A0 offer substantial benefits for high-power applications and support progress in the fields of Industry 4.0 equipment and industrial automation. Understanding and using important datasheet parameters correctly can enable engineers to design efficient and reliable power electronic systems based on SiC devices. 

As SiC technology continues to evolve, its adoption will likely expand, driving forward advances in energy efficiency and system performance across various industries.