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Description
Commercially available, low dI/dt (0.4 kA/µs), silicon thyristors have previously been investigated as fast, high-power, switches. Fast switching is achieved by applying a steeply rising (dV/dt > 1 kV/ns) overvoltage pulse across the thyristor’s main electrodes: fast turn-on occurs when the voltage amplitude is twice the static breakdown voltage. Under such conditions, the thyristor goes into the conductive state within ~200 ps. Current rise rate up to 130 kA/µs, limited by the discharge circuit, was obtained for commercial thyristors with impact-ionization triggering mode. GTO like thyristors, comprising of highly interdigitated gate and cathode structure, similarly to a GTO, are used at CERN for an emergency beam dump system. These devices, the 5STH-20H450002 (4.5 kV, 18 kA/µs), were developed by ABB semiconductors. Nevertheless, a new principle of operation such as impact-ionization triggering can enhance dI/dt capability and reduce turn-on delay time. This work reported in this paper is aimed at studying the operation of the GTO like thyristors triggered in impact-ionization wave mode. A SOS generator providing a dV/dt of several kV/ns was used as a source of triggering pulses. Under such triggering conditions a thyristor switching time of approximately 200-300 ps was observed. Maximum discharge parameters were obtained for two series connected thyristors at charging voltage of 10 kV, and capacitor stored energy of ~300 J: peak current of 43 kA, dI/dt of 115 kA/µs, FWHM of 1.5 µs. The switching efficiency was 92%.
