Superfast Thyristor-Based Switches Operating in Impact-Ionization Wave Mode.

The process of triggering thyristors by an overvoltage pulse with a short rise time was investigated. Low-frequency commercial thyristors of tablet design with diameters of silicon wafers of 32–56 mm and an operating voltage of 2–2.4 kV dc were used in the experiments. An external overvoltage pulse was applied across the thyristor main electrodes, which ensured a voltage rise rate from 0.5 to 6 kV/ns within a few nanoseconds. Under such conditions, the thyristor closing process occurred due to initiation and propagation of a fast ionization front across the semiconductor structure. The time of switching the thyristor from the blocking state to the conducting state was within 200–400 ps. The thyristor-based switches operated in this mode were tested in two discharge circuits. In the first circuit, an assembly of nine 2-kV and 40-mm thyristors connected in series switched a 2- \mu \textF capacitor, which was charged to a voltage of 20 kV and to a resistive load of 0.17~\Omega . The following results were obtained: discharge current amplitude of 45 kA, maximum current-rise rate of 134 kA/ \mu \text{s} , current rise time (0.1–0.9 level) of \sim 0.4~\mu \text{s} , pulse duration (FWHM) of \sim 1~\mu \texts , and switching efficiency of 0.85. In the second circuit, the switch contained two 2.4-kV and 56-mm thyristors connected in series. A 400- \mu \textF capacitor, which was charged to a voltage of 5 kV, was switched to a resistive load of 0.026~\Omega . The following discharge parameters were obtained: discharge current amplitude of 114 kA, maximum current-rise rate of 32 kA/ \mu \texts , current rise time (0.1–0.9 level) of \sim 5~\mu \texts , pulse duration (FWHM) of \sim 20~\mu \texts , and switching efficiency of 0.96. [ABSTRACT FROM AUTHOR]