A thyristor continues to conduct even after the gate pulse is removed. What is the main reason for this behavior?
The device latches ON after triggering
A thyristor, or silicon-controlled rectifier (SCR), is a four-layer PNPN semiconductor switch that is turned ON by a brief pulse of gate current.
Internally it behaves like two interconnected transistors whose outputs feed each other, forming a regenerative positive-feedback loop.
Once the anode current rises above the holding value, this feedback drives both internal transistors fully into conduction and sustains the current by itself.
Because of this internal latching action, the gate loses all control after triggering, so the device keeps conducting even when the gate pulse is removed.
It does not act like a fuse; a fuse breaks the circuit, whereas the thyristor stays closed, and it turns OFF only when the anode current falls below the holding current.
It also does not need continuously increasing gate current, and the reverse-biased-junction idea does not apply, since it is the latched forward conduction, not a blocking junction, that keeps it ON.
Hence, the answer is The device latches ON after triggering.
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