Burst Triggering the Thyristor Tutorial
The top waveform shows the ac supply.
The middle waveform shows the switch operation.
When the switch is closed, the gate and anode go positive on the first positive half cycle, and the thyristor conducts during this period.
On the next half cycle they go negative and no current flows.
As long as the switch is closed, the thyristor conducts on the positive half cycles only.
When the switch is opened, the thyristor ceases to conduct on the next negative half cycle, and remains non conducting.
The bottom waveform shows the current through the thyristor and lamp.
The current comes in BURSTS.
If the lamp is replaced by a heater, and the switch replaced by a thermostat then it would provide automatic temperature control for an oven.