Figure of merit for selecting super-junction MOSFETs in high efficiency voltage source converters

Silicon super-junction MOSFETs have very low on-state resistances and fast switching characteristics. However, their use in voltage-source converters is hindered by the poor reverse recovery performance of their body drain diode and an adverse output capacitance characteristic. These both act to increase the overall switching loss. The on-state resistance and output capacitance characteristics of super junction devices are both related to the area of the silicon die. As this increases, the on-state resistance decreases but the output capacitance increases. A figure of merit is evaluated with both predicted and experimental results using a 400-V, DC-DC synchronous buck-converter operating over a range of output currents and switching frequencies.