Whole-cycle control of AC power to small electric heaters

Abstract

When a triac is used to control the flow of AC power to a heater, burst control is preferred to phase-angle control, but cannot be used if the thermal system reacts quickly to changes in heat input. This paper describes an arrangement which allows zero-voltage triggering of the triac, so avoiding the problems associated with phase control, but is usable with plants whose thermal time-constants are as short as 5 s (with 50Hz supply) or less. Its hardware requirements are no more than those of burst or phase control. Schematic circuits are given for use with both digital and analogue control systems.