Video narration
How can a brief gate pulse start a current that keeps flowing after the pulse ends? Like a momentary START button on a self-holding relay, one press begins a state that continues after you let go. A thyristor, or SCR, works similarly-but only when forward-biased, with voltage favoring current from anode to cathode. A suitable gate current triggers it. Inside, conduction reinforces itself. This regenerative feedback rapidly turns the thyristor into a conducting path, allowing the main current to flow. The gate pulse starts conduction; it does not sustain it. The main current must rise enough for the device to latch. Once latched, removing the gate signal does not turn it off; current through the device keeps it conducting. To turn it off, anode current must fall below the holding current-the minimum current that keeps it on through the device.