Types Thyristor

electronic symbol light-activated scr (lascr)

photothyristors activated light. advantage of photothyristors insensitivity electrical signals, can cause faulty operation in electrically noisy environments. light-triggered thyristor (ltt) has optically sensitive region in gate, electromagnetic radiation (usually infrared) coupled optical fiber. since no electronic boards need provided @ potential of thyristor in order trigger it, light-triggered thyristors can advantage in high-voltage applications such hvdc. light-triggered thyristors available in-built over-voltage (vbo) protection, triggers thyristor when forward voltage across becomes high; have been made in-built forward recovery protection, not commercially. despite simplification can bring electronics of hvdc valve, light-triggered thyristors may still require simple monitoring electronics , available few manufacturers.

two common photothyristors include light-activated scr (lascr) , light-activated triac. lascr acts switch turns on when exposed light. following light exposure, when light absent, if power not removed , polarities of cathode , anode have not yet reversed, lascr still in on state. light-activated triac resembles lascr, except designed alternating currents.