IGBT-based switching modules for laser applications

This paper presents the design of IGBT-based switching modules for a nitrogen gas laser. First, the CC-topology, which drives the laser, is discussed and simulated. Simple models of the laser tube and the switch are presented. The comparison of the simulation with experimental data shows good accuracy. The results are used to discuss the influence of the parasitic inductance and the capacitances on the laser tube behavior. Cascades with an 11-cell series connection based on different IGBT-chips (1700 V and 1200 V) have been built up and measured. The focus of the design is the high speed synchronous switching of all switching cells. Therefore, the design of a pulse transformer-based gate drive and a symmetrization network is presented. The module equipped with the four parallel 1200 V/35 A-IGBTs per cell produces the highest switching power. Among the variants, the switch peak current is up to 700 A at blocking voltages of up to 13.2 kV in the real environment of the nitrogen laser. The switch current slope reaches up to 30 A/ns and the laser tube current up to 1.8 kA. The variant with 1200 V/35 A-IGBTs produces an output energy which is about 15 % higher compared to the former MCT-based switch. Furthermore, a modified CCtopology for lower blocking voltage is investigated. The IGBT-based switches are able to replace the MCT-switches in this application. Between the different switches a tradeoff has to be done between high output energy and the effort for the assembly.