A thyristor, also called a silicon controlled rectifier (SCR), is a 4-layer device that acts like a diode, that is, conducts only one direction; but, it doesn't conduct at all unless triggered during the forward half cycle. Hence, it is the device used in light dimmers, where the timing of the gating voltage controls how much of the half cycle it conducts.
More: once the forward half cycle ends, the reverse voltage across cathode and anode shuts it off automatically and it will not conduct on the next forward half cycle unless it gets another trigger pulse.
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Old TV literature, New York World's Fair, and other miscellany
Last edited by old_tv_nut; 03-20-2017 at 11:36 AM.
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