Pulsed-duty characterization of turn-off for a population of SCRs and the effect of variation on equalization circuit design

Turn-off characteristics of silicon-controlled rectifiers (SCRs) drive the design of snubber circuits for single devices in power converters. Turn-off characteristics also drive the design of equalization circuits for series-connected devices in power converters. For single devices, the important characteristics are peak recovery current, recovery time, and recovered charge. These characteristics are also important for series-connected devices, but it is the variation in these characteristics that define the equalization requirements. In fact, these variations are used to determine the size and power dissipation of the equalization circuit. A population of SPCO 402b pulse-rated silicon controlled rectifiers was tested and recovery characteristics were measured. The differences in recovery characteristics were tabulated and discussed. A method of equalization circuit design based on circuit variations was discussed and circuit design trades are made in light of the variations in recovery characteristics.