REVERSE PHASE CONTROL POWER SWITCHING CIRCUIT WITH OVERLOAD PROTECTION

摘要

In one embodiment of the invention, a reverse phase control power switching circuit for controlling the flow of current through a load from an AC source comprises a sensing bridge in series with the load and the AC source. The conductive state of the sensing bridge is responsive to a pulse generator and a zero creasing detection and overload protection means. Phase control means coupled to the pulse generator determines turn off of the sensing bridge is reset by the zero crossing detection and overload protection means. Responsive to a load current condition exceeding a maximum current caused by an overload or a short, the zero crossing detection and overloading protection network terminates conduction of current through the sensing bridge. The sensing bridge starts conducting current to the load at the beginning of the AC cycle and continues to conduct to a desired AC voltage phase angle or earlier if an excessive current condition caused by an overload condition or a short occurs.