Power control system

Claim 1

A control system for effecting the selective energization of a load comprising a selectively energizable a.c. power switch having a control terminal and a pair of power terminals for coupling the load to an a.c. power source, one of said power terminals being connectable to the a.c. power source and the other power terminal being connectable to the load, first trigger means coupled to said control terminal for supplying energizing signals thereto from the a.c. power source to render said a.c. power switch conductive only during a.c. half cycles of a first predetermined polarity while maintaining said control terminal electrically isolated from the a.c. power source during a.c. half cycles of a second predetermined polarity opposite to said first predetermined polarity, said first trigger means includes a half-wave rectifier diode coupled to said control terminal of said a.c. power switch for supplying energizing signals thereto of said first predetermined polarity for rendering said a.c. power switch conductive, and second trigger means coupled to said control terminal for supplying energizing signals thereto to render said a.c. power switch conductive during a.c. half cycles of said second predetermined polarity responsive to conduction of said a.c. power switch during a.c. half cycles of said first predetermined polarity, said second trigger means includes a selectively energizable unidirectional power switch having a pair of power terminals, one of said power terminals being connected to the a.c. power source in parallel relationship with said one power terminal of said a.c. power switch and the other power terminal being coupled to said control terminal of said a.c. power switch for supplying trigger signals thereto when said unidirectional power switch is in a conductive state, said unidirectional power switch includes a control element adapted to receive trigger signals subsequent to the application of energizing signals to said control terminal of said a.c. power switch, whereby said unidirectional power switch is selectively rendered conductive responsive to energization of said a.c. power switch, energy storage means comprising a capacitor is coupled to said half-wave rectifier diode for storing energy while said half-wave rectifier dIode is supplying energizing signals to said control terminal of said a.c. power switch, said energy storage means is coupled to said control element of said unidirectional switch and is adapted to discharge stored energy therethrough for a predetermined time for rendering said unidirectional power switch conductive during a.c. half cycles of said second predetermined polarity, thereby maintaining said a.c. power switch conductive, discharge of said capacitor is initiated during the a.c. half cycle of said first predetermined polarity when said a.c. power switch is in a conductive state to effect energization of said unidirectional power switch upon the initiation of the a.c. half cycle of said second predetermined polarity.