Power control system with improved phase control

摘要

An improved phase-controlled power control apparatus includes a semiconductor switching element for varying the effective power delivered to a load from the power lines. The conduction angle of the semiconductor power switch element is varied from a nominal angle to compensate for changes in power line voltage and for changes in load current. The amount of load current flow is continuously compared to the power line voltage to detect any overcurrent condition, even very close to the zero-crossing of the power line voltage. The shape of the transition from load current on to load current off (or vice versa) in controlled to minimize audible noise from the load. The load current can be shared between a plurality of compatible power control sections.