Power semiconductor devices-examination of subcycle surge current ratings as needed for fuse selection

It is well recognized that subcycle Irms²t ratings for high power semiconductor devices and current limiting fuses are not equivalent because the former are based on single half sine waves while the latter are based on near triangular waves as associated with current interruption. Also the difference becomes more pronounced for thyristors as opposed to rectifier diodes due to the finite spreading rate of the turned on region which produces additional heating effects. Although the published characteristics and application data from fuse manufacturers are usually adequate, the circuit designer may find difficulty applying this information to that of the power semiconductor device. This paper examines concepts for determining reliable subcycle surge ratings including proof testing the highest power “state of the art” thyristors and makes recommendation for improvement and economizing of testing