Applications of silicon carbide JFETs in power converters

Silicon carbide (SiC) JFET devices exhibiting normally-off characteristics have become commercially available, enabling their adoption into power supply products. In this paper, the synchronous rectification characteristics of SiC JFETs are investigated and their overall performance in single phase power factor correction (PFC) circuits is measured. Efficiency comparisons in a high efficiency telecommunications power supply demonstrate superior performance of 1200V SiC JFETs compared to 900V silicon MOSFETs. A minimal switch, high voltage PFC topology, requiring 1200V devices, is evaluated; however the slew rate of the SiC JFETs is insufficient to exceed the efficiency of other topologies. Initial testing is conducted in a three-phase cycloconverter application. Different switching behaviour is observed with SiC JFETs than silicon MOSFETs. The effect is shown to be due to the JFET's lower output capacitance which also leads to reduced switching loss. It is concluded that SiC JFETs perform at a similar level to 600V silicon MOSFETs and better than 900V MOSFETs, whilst being a 1200V device. These aspects, coupled with their ability to conduct in either direction make the SiC JFET particularly well suited to cycloconverter applications.