Advanced semiconductor switches for EM launchers

Abstract

Electric launchers may be energized by switching pulses of variable magnitude and time from a pulsed alternator or a pulse forming network. In order to achieve the desired muzzle energy, the switches must withstand the action of the current pulse: the square of current integrated over time. High pressure spark gap switches and vacuum switches of various architectures have been utilized in most of the launcher development programs. Advances in semiconductor technology hold a promise of replacing these large and bulky switches with solid state switches which may become leading candidates for future combat systems applications. The US Army Research Laboratory has been testing and evaluating solid state switches of various types for several different applications. One type of semiconductor switch that was tested and evaluated is a thyristor that is 125 mm in diameter made by Silicon Power Corporation (SPCO). When a thyristor with this large diameter is turned on, it is necessary to develop and spread plasma uniformly and quickly across the wafer. This ensures that the current from the anode to the cathode is uniformly distributed, and not concentrated in local hot spots where an excessive current density could cause overheating and damage. This plasma spread can be controlled by the design of the gate structure and the triggering technique. Thyristors with different gate structures were tested and compared. The experimental findings of the turn-on characteristics and the maximum current capabilities for each design are presented. The status of futuristic wide band gap semiconductor switch technology is also reviewed.