HIGH RELIABILITY AC LOAD SWITCHING CIRCUIT
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.