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Experiments were conducted to study the high energy, high di/dt pulse-switching characteristics of SCR's with and without the amplifying gate. High di/dt, high-energy single-shot experiments were first done. Devices without the amplifying gate performed much better than the devices with the amplifying gate. A physical model is presented to describe the role of the amplifying gate in the turn-on process, thereby explaining the differences in the switching characteristics. The turn-on area for the failure of the devices was theoretically estimated and correlated with observations. This allowed calculation of the current density required for failure. Since the failure of these devices under high di/dt conditions was thermal in nature, a simulation using a finite-element method was performed to estimate the temperature rise in the devices. The results from this simulation showed that the temperature rise was significantly higher in the devices with the amplifying gate than in the devices without the amplifying gate. From these results, the safe operating frequencies for all the devices under high di/dt conditions was estimated. These estimates were confirmed by experimentally stressing the devices under high di/dt repetitive operation.

A study of thyristor performance at low temperatures is presented. A 1200-V, 560-A inverter thyristor is evaluated for its forward breakover voltage and forward conduction voltage drop. Actual and computed values in terms of the temperature reduction from 25 to -180 degrees Celsius are compared. Results show a negative temperature coefficient for the forward breakover voltage and a larger value of forward voltage drop at 90 K than at room temperature.

Certain applications for pulse power require narrow, high current pulses for their implementation. This work was performed to determine if MOS controlled thyristors (MCTs) could be used for these applications. The MCTs were tested as discharge switches in a low inductance circuit delivering 1[micro]s pulses at currents between roughly 3 kA and 11kA, single shot and repetitively at 1, 10, and 50 Hz. Although up to 9000 switching events could be obtained, all the devices failed at some combination of current and repetition rate. Failure was attributed to termperature increases caused by average power dissipated in the thyristor during the switching sequence. A simulation was performed to confirm that the temperature rise was sufficient to account for failure. Considerable heat sinking, and perhaps a better thermal package, would be required before the MCT could be considered for pulse power applications. Index Terms--High power, power semiconductor switching, reliability, repetitive pulsing.

A method is described for analyzing skin impedance data and applied to the determination of a steady-state electrical model for intact human skin. An algorithm is presented for the analytical procedure, Bode analysis, and a sample impedance function is obtained. Bode plots are employed to synthesize a passive equivalent circuit from sample measurements of "black box" skin impedance magnitude and phase angle, and representative values for the circuit elements are presented. [ABSTRACT FROM AUTHOR]