A high-power light-activated thyristor

Abstract

A 2000V, 800A light-activated thyristor, suitable for use in high power circuitry of the type required by the electric utility industry is described. Unlike a conventional thyristor which is turned on by an electrical signal to the gate electrode, this device is turned on by an optical pulse, from a solid state light-source, that is conveyed to the silicon device via a light pipe. The key design objectives were to create a device structure capable of being fired by a low energy light pulse in a reliable manner, while maintaining a short and uniform delay time and a dV/dt rating in excess of 300V/µsec. A design approach is described that has resulted in a better understanding of the physics of firing a high power thyristor with a small light energy. Considered are gate amplification, the area of illuminated silicon, the duration of the light pulse and the conductivity type and the surface preparation of the light sensitive area. Evaluation data shows that a light pulse with only 0.3 µJ of energy can be used to fire the thyristor, reliably and with low switching loss, with uniform delay times of < 1 µsec and turn-on times of < 3.5 µsec. A quantity of these devices is being produced for use in an experimental power electronics system.