High reliability ac load switching circuit

Abstract

A high reliability AC load switching circuit is disclosed. In some embodiments, the AC load switching circuit includes a high-speed switch connected between the load and the voltage source, a cutoff switch connected between the load and the voltage source in parallel with the high-speed switch, and a level detector connected to the voltage source and to a control input of the high-speed switch. The high-speed switch may be a solid-state switch, for example, a TRIAC or a bidirectional switch, and the cutoff switch may be an electromechanical switch, for example, a relay. In some embodiments a snubber is connected in parallel with a solid-state switch. In some embodiments a microcontroller is connected to an eletromechanical switch and the level detector. In some embodiments, both a first cutoff switch and a second cutoff switch are used.

1 . A switching circuit to selectively connect a load to a voltage source, the switching circuit comprising:
 a high-speed switch connected between the load and the voltage source;   a cutoff switch connected between the load and the voltage source in parallel with the high-speed switch; and   a level detector connected to the voltage source and to a control input of the high-speed switch.   
     
     
         2 . The switching circuit of  claim 1  further comprising a snubber connected in parallel with the high-speed switch. 
     
     
         3 . The switching circuit of  claim 1  further comprising a microcontroller connected to the cutoff switch and the level detector. 
     
     
         4 . The switching circuit of  claim 3  wherein the high-speed switch comprises solid-state switch. 
     
     
         5 . The switching circuit of  claim 4  wherein the solid-state switch comprises a triode for alternating current (TRIAC). 
     
     
         6 . The switching circuit of  claim 4  wherein the solid-state switch comprises bidirectional switch. 
     
     
         7 . The switching circuit of  claim 3  further comprising a snubber connected in parallel with the high-speed switch. 
     
     
         8 . The switching circuit of  claim 3  wherein the cutoff switch comprises an electromechanical switch and further comprising:
 a transistor connected to the microcontroller; and 
 a resistor connected between the transistor and the electromechanical switch. 
 
     
     
         9 . The switching circuit of  claim 8  wherein the high-speed switch comprises a solid-state switch. 
     
     
         10 . The switching circuit of  claim 9  wherein the solid-state switch comprises a triode for alternating current (TRIAC). 
     
     
         11 . The switching circuit of  claim 9  wherein the solid-state switch comprises bidirectional switch. 
     
     
         12 . The switching circuit of  claim 8  further comprising a snubber connected in parallel with the high-speed switch. 
     
     
         13 . A switching circuit to selectively connect a load to a voltage source, the switching circuit comprising:
 a high-speed switch connected between the load and the voltage source;   a first cutoff switch connected between the load and the voltage source in parallel with the high-speed switch;   a second cutoff switch connected in series with the high-speed switch; and   a level detector connected to the voltage source and to a control input of the high-speed switch.   
     
     
         14 . The switching circuit of  claim 13  further comprising a snubber connected in parallel with the high-speed switch. 
     
     
         15 . The switching circuit of  claim 13  further comprising a microcontroller connected to the first cutoff switch, the second cutoff switch, and the level detector. 
     
     
         16 . The switching circuit of  claim 15  wherein the high-speed switch comprises a solid-state switch. 
     
     
         17 . The switching circuit of  claim 16  wherein the first cutoff switch, the second cutoff switch, or both cutoff switches comprise an electromechanical switch. 
     
     
         18 . The switching circuit of  claim 17  wherein the electromechanical switch comprises a relay. 
     
     
         19 . The switching circuit of  claim 16  further comprising a snubber connected in parallel with the solid-state switch. 
     
     
         20 . The switching circuit of  claim 16  wherein the second cutoff switch is connected between the solid-state switch and the voltage source. 
     
     
         21 . The switching circuit of  claim 16  wherein the second cutoff switch is connected between the solid-state switch and the load. 
     
     
         22 . A method of selectively connecting a load to an AC voltage through a switching circuit, the method comprising:
 turning on a solid-state switch between the voltage source and the load at zero-crossing of the AC voltage; and   activating a first electromechanical switch connected in parallel with the solid-state switch after the turning on of the solid-state switch.   
     
     
         23 . The method of  claim 22  further comprising:
 deactivating the first electromechanical switch; and 
 turning off the solid-state switch. 
 
     
     
         24 . The method of  claim 22  further comprising activating a second electromechanical switch connected in series with the solid-state switch prior to turning on the solid-state switch and in response to activation of the switching circuit. 
     
     
         25 . The method of  claim 24  further comprising:
 deactivating the first electromechanical switch; 
 turning off the solid-state switch; and 
 deactivating the second electromechanical switch.