Phase-fired controller

[1] It works by modulating a thyristor, SCR, triac, thyratron, or other such gated diode-like devices into and out of conduction at a predetermined phase angle of the applied waveform.

Phase-fired controllers take their name from the fact that they trigger a pulse of output at a certain phase of the input's modulation cycle.

To achieve a "boost"-like effect, the PFC designs must be derated such that the maximum present at the input is higher than the nominal output requirements.

To account for this, a phase-fired control must be able to provide some degree of extra voltage to draw the same heating current through the element.

In modern, usually high-power, equipment, the transformer is replaced with phase-fired controllers connecting the load directly to the mains, resulting in a substantially cheaper and lighter system.

For industrial ovens and furnaces the input is often the national grid AC, which is itself electrically referenced to ground.

With many high-power items of equipment running from three-phase 415 V[clarification needed], high-current inputs and having any enclosure or framework present earthed (grounded), this is a serious risk that must be carefully assessed.