Solid State Spark Gap Replacement Switches

Improvements in solid state high voltage switching technology now make it feasible to replace triggered spark gap switches, used in many medical and commercial applications to switch tens of kilovolts and thousands of amperes, with compact solid-state switches. We have developed a multi-stage high voltage solid-state switch that is triggered by a single 10 V isolated trigger pulse to only one stage, thereby reducing the size and decreasing the triggering complexity of the switch. The switch uses small 5300 V thyristors capable of 14 kA peak currents and >25 kA/mus rate of current risetimes. The short turn-on delay, less than 200 ns, makes the switch suitable for crowbar applications. This paper will include a description of the solid-state switch and triggering system, as well as show data from a 24 kV system using both the spark gap and the solid-state replacement switch to discharge a 0.15 muF capacitor at 1.5 pps. The switch current has a ringing discharge with a peak forward value of 10 kA and a quarter cycle time of 500 ns. The overall size of the solid state switch, including the fins required for convective cooling at several pps operation, is 2"times4"6.5". These switches are used commercially in Lithotripters, a medical system that effectively treats renal and urinary calculus by fragmentation of kidney and ureteral stones