High Voltage Thyristor Switch For Pulse Power Applications

Investigations were made to replace spark gaps by thyristors as main switches for electromagnetic launching applications. Experiments with different kinds of thyristors showed that reverse blocking thyristors with optimized turn-on capability are ideal candidates for pulse power applications. They have an interdigitated gate structure, which enables a high current rate (> 700 A/ps), and a sufficient current capability (Imax = 90 kA). Since the blocking voltage of the used device is limited to 3.0 kV several thyristors have to be put in series to apply the switch at the operating voltage of 10 kV. In order to avoid a serial configuration of thyristors a 11 kV-thyristor device has been developed, by stacking thyristor chips one upon the other and surrounding the whole stack by a common housing. This device has the same current and current rate capability as an ordinary serial configuration of thyristors, whereas the volume and the inductance are strongly reduced. Due to its compactness and a newly developed gate unit with a high current rate and a dispersion less than 50 ns there is no requirement to protect the newly developed device by a snubber circuit (saturable reactors, freewheel diode, etc.). The compact thyristor stack was applied as main switch to a 50 kJ-capacitor. Together with a diode crowbar switch, also based on multichip technology, and an inductance, a pulse forming unit for electromagnetic launching applications has been built and tested successfully.