Comparative electrothermal analysis between SiC Schottky and silicon PiN diodes: Paralleling and thermal considerations

In power modules with high current ratings where several devices are required for parallel connection, electrothermal balance between the parallel devices is a very important consideration. This paper investigates the impact of electrothermal imbalance between parallel connected devices on the thermal stability of the parallel pair. Under investigation are parallel connected 600 V silicon PiN and silicon carbide Schottky diodes. The electrothermal imbalance between the parallel devices was introduced by setting different initial junction temperatures and using different thermal boundary conditions i.e. different case temperatures. The effect of the diode technology on the thermal stresses of the complementing transistor is also assessed. The results show that silicon PiN diodes operate at lower junction temperatures because of the higher zero-temperature coefficient points in the forward current characteristics, however, the complementing MOSFETs are more thermally stressed since the reverse recovery of the diode causes current overshoots in the complementing transistor. It is also shown that SiC Schottky diodes exhibit more electrothermally stable operation under electrothermal imbalance when connected in parallel. Parallel connected SiC Schottky diodes with different initial junction temperatures and different thermal boundary conditions (case temperatures) exhibit better temperature convergence/stability compared to silicon PiN diodes. The temperature convergence in parallel SiC Schottky diode pairs is due to the lower Zero-Temperature Coefficient (ZTC) point compared with the PiN diode pairs, which means more equal current sharing in parallel SiC diodes.