Abstract: An improved method and apparatus for handling the large load currents which occur with overloads, short circuits, and momentary overcurrents such as in starting motors or cold incandescent lamp filaments. The method involves turning the load current off when an overcurrent is detected, and then back on again before the end of the half-cycle in which the overcurrent occurred. This allows more current to flow during the half-cycle without the need to increase the peak current capability of the power-handling components. With an incandescent lamp load, this results in more rapid lamp brightening without the need for larger, more expensive components. Several embodiments are disclosed which respond to different features of the power line voltage cycle, including a very low-cost microprocessor circuit and power supply.

Abstract: 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.