SLUAB11 November 2025 AMC23C12-Q1 , TMCS1126-Q1 , UCC21750-Q1
To analyze the mechanisms of an SCT 1, the half-bridge model is shown in Figure 2-1. The two SiC MOSFETs SHS and SLS are controlled by a gate driver unit (GDU), respectively. Furthermore, two capacitors provide energy for the converter: the capacitance CC provides the needed energy for the current commutation between the two SiC MOSFETs SHS and SLS, while the capacitance CB is used as bulk filter at the output of the converter. The inductances Lσ,C and Lσ,B represent the sum of parasitic inductances of capacitors, MOSFETs and PCB traces. A common circuit breaker SB connects the high-voltage battery Ubatt to various power electronic devices.
In the event of a short circuit, it is crucial to isolate the fault to avoid further damage, such as fire hazards. Using the breaker SB to disconnect the fault disrupts the operation of other functioning devices connected to the battery. One idea is to incorporate an additional mechanical or electronic fuse in each converter; however, this approach increases costs, which is not great in the price-sensitive automotive application. Consequently, there is a pressing need for a reliable and cost-effective short-circuit protection scheme to prevent thermal incidents.
Two of the short-circuit detection methods utilize an additional current sensor. As discussed in the Section 1.3, the current sensor is placed between the two capacitors CC and CB.
For the measurement, two SiC MOSFETs SHS and SLS form the half-bridge topology. The drain and source pins of the MOSFET SLS are soldered together to make sure a low impedance short circuit to simulate SCT 1 on MOSFET SHS. At time t0, the GDU of MOSFET SHS gets the turn-on command and the gate-source voltage of high-side SiC MOSFETs uGS starts to increase.
The current slope diSC/dt is dependent on various parameters such as stray inductances and capacitances of the SiC MOSFETs [16]. The current iSC reaches the peak at the time t1 and decreases afterwords. The decreasing current can be explained due to the self-heating of the SiC MOSFET die, caused by losses and therefore increasing drain-source resistance [16].
Even though the current continues to decrease, more and more energy is dissipated in the SiC MOSFET as the drain-source voltage of high-side SiC MOSFETs uDS stays high. Hence, the MOSFET keeps continuously increasing the temperature. At time t2, the SiC MOSFET reaches the critical junction temperature and gets damaged in a low impedance state. As the current iSC is not limited by the drain-source resistance anymore, iSC starts to increase again. From now on, the short circuit cannot be isolated by the MOSFETs and as long as the battery provides energy, this short circuit is a potential risk of fire and smoke hazards. Therefore, there is a need for short-circuit protection to prevent damage to the MOSFETs. Current sensing methods such as shunt-based detection and hall-effect sensor- based detection, along with the voltage sensing method like the desaturation method, are selected as protection methods for analysis.