Condition responsive solid-state switch

A switch for automatically controlling the supply of power from a voltage source to a load based on an environmental condition to which the switch is subjected comprising:

• a solid-state switching component for coupling between the voltage source and the load to supply an interruptible current path therebetween and having a trigger input for actuation of the switching component so as to selectively control the switching component between an on (closed) state and an off (open) state;
• an off timer circuit for coupling between the voltage source and the load to receive power therefrom when the switching component is in its off state and for periodically generating power pulses of short duration with the period between consecutive power pulses being much greater than the duration of each power pulse, the off timer circuit having an output at which the power pulses generated thereby are supplied;
• a sensing circuit connected to the output of the off timer circuit and powered by the power pulses, the sensing circuit including a sensor for sensing the environmental condition during each power pulse, a first signal generator connected to the sensor for generating a first signal varying based on the sensed condition, a reference signal generator for generating a reference signal during each power pulse, and a comparator coupled to the first signal generator and the reference signal generator for comparing the first signal with the reference signal and for generating a trigger signal for each power pulse when a predetermined relationship exists between the reference signal and the first signal;
• means coupled between the comparator and the trigger input of the switching component for conveying the trigger signal to the trigger input of the switching component such that the switching component is actuated to its on and off states as a function of changes in the sensed condition;
• an on-timer circuit for coupling between the voltage source and the load to receive power therefrom when the switching component is in its on state and for periodically momentarily supplying an interrupt signal;
• and
• means coupled between the on-timer circuit and the trigger input of the switching component for connecting the on timer circuit to the trigger input of the switching component, and for actuating the switching component to its off state if the switching component was previously in its on state to power the off timer to again supply the power pulses, whereby the environmental condition continues to be sensed periodically and the trigger signal continues to be generated periodically based on the sensed condition.