Reverse-phase-control power switching circuit and method

A method for controlling the angle of conduction of current flow through a load from an A.C. source, comprising the steps of:

• (a) providing a power switching means in electrical series connection with the load and the source;
• (b) detecting each zero crossing of the A.C. signal waveform of the source to provide a first signal;
• (c) enabling the power stitching means to a turned-on condition to cause a flow of current through the load commencing substantially at each zero crossing and responsive to each occurrence of the first signal;
• (d) disabling the power switching means to a turned-off condition to terminate the flow of current through the load from the source at the end of a selected time interval after the occurrence of each first signal and prior to the occurrence of a next subsequent first signal;
• and
• (e) selecting the time interval, between each repetition of steps (c) and (d), in each A.C. source signal waveform half-cycle, during which the power switching means conducts current to establish the desired conduction angle of current flowing through the load.

A reverse-phase-control power switching circuit for controlling the magnitude of current current flow through a load from an A.C. source, comprising:

• power switching means, having an input and a controlled-conduction circuit in electrical series connection with said load and said source, for enabling a flow of current through said load responsive to a first condition at said input, and for disabling current flow through said load responsive to a second condition at said input;
• detector means for providing a first signal responsive to each zero crossing of the A.C. signal waveform of said source;
• monitor means for non-magnetically generating a second signal when a monitored characteristic of said power switching means, related to the instantaneous magnitude of load current flowing therethrough, exceeds a reference value;
• and
• drive switch means, receiving said first and second signals, for providing said first condition at said power switching means input substantially upon receipt of said first signal and for providing said second condition at said power switching means input responsive to the first occurring one of (a) said second signal and (b) the elapsation of a preselected time interval after the occurrence of each first signal and prior to the occurrence of the next-subsequent first signal.