Automatic transfer switch circuits and control methods

1. An automatic transfer switch circuit comprising:

a first voltage input having a line terminal and a neutral terminal;

a second voltage input having a line terminal and a neutral terminal;

a voltage output having a line output terminal and a neutral output terminal;

a first relay coupled to the line terminal of the first voltage input and the line terminal of the second voltage input;

a second relay coupled to the neutral terminal of the first voltage input and the neutral terminal of the second voltage input;

a third relay coupled between the line output terminal and at least one of the first relay and second relay;

a fourth relay coupled between the neutral output terminal and at least one of the first relay and the second relay; and

a controller coupled to the relays to control a state of each of the relays.

2. The circuit of claim 1 , wherein the first relay includes a first output terminal and a second output terminal, the first relay is configured to couple the line terminal of the first voltage input to the first output terminal of the first relay when the first relay is in a first state, and the first relay is configured to couple the line terminal of the second voltage input to the second output terminal of the first relay when the first relay is in a second state.

3. The circuit of claim 2 , wherein the second relay includes a first output terminal and a second output terminal, the second relay is configured to couple the neutral terminal of the first voltage input to the first output terminal of the second relay when the second relay is in a first state, and the second relay is configured to couple the neutral terminal of the second voltage input to the second output terminal of the second relay when the second relay is in a second state.

4. The circuit of claim 3 , wherein the third relay is configured to couple the first output terminal of the first relay to the line output terminal of the voltage output when the third relay is in a first state, and the third relay is configured to couple the second output terminal of the first relay to the line output terminal of the voltage output when the third relay is in a second state.

5. The circuit of claim 3 , wherein the fourth relay is configured to couple the first output terminal of the second relay to the neutral output terminal of the voltage output when the fourth relay is in a first state, and the fourth relay is configured to couple the second output terminal of the second relay to the neutral output terminal of the voltage output when the fourth relay is in a second state.

6. The circuit of claim 3 , wherein the third relay is configured to couple the first output terminal of the first relay to the line output terminal of the voltage output when the third relay is in a first state, and the third relay is configured to couple the second output terminal of the second relay to the line output terminal of the voltage output when the third relay is in a second state.

7. The circuit of claim 3 , wherein the fourth relay is configured to couple the first output terminal of the second relay to the neutral output terminal of the voltage output when the fourth relay is in a first state, and the fourth relay is configured to couple the second output terminal of the first relay to the neutral output terminal of the voltage output when the fourth relay is in a second state.

8. The circuit of claim 1 , wherein the line output terminal of the voltage output and the neutral output terminal of the voltage output are coupled to an input of a power supply unit.

9. A power supply unit, wherein the circuit of claim 1 is integrated into the power supply unit.

10. The circuit of claim 1 , wherein the first voltage input is coupled to a primary power source and the second voltage input is coupled to a secondary backup power source.

11. The circuit of claim 1 , wherein at least one of the relays includes a 1A+1B relay having a normally open contact and a normally closed contact.

12. The circuit of claim 1 , wherein the third relay is a single-pole, dual-throw relay and the fourth relay is a single-pole, dual-throw relay.

13. The circuit of claim 1 , wherein the four relays are identical to one another.

14. A method of operating an automatic transfer switch circuit, the circuit including a first voltage input having a line terminal and a neutral terminal, a second voltage input having a line terminal and a neutral terminal, a voltage output having a line output terminal and a neutral output terminal, a first relay coupled to the line terminals of the first voltage input and the second voltage input, a second relay coupled to the neutral terminals of the first voltage input and the second voltage input, a third relay coupled between the line output terminal and at least one of the first relay and the second relay, and a fourth relay coupled between the neutral output terminal and at least one of the first relay and the second relay, the method comprising:

placing the first relay in a first state to couple the line terminal of the first voltage input to a first output terminal of the first relay; and

placing the first relay in a second state to couple the line terminal of the second voltage input to a second output terminal of the first relay.

15. The method of claim 14 , further comprising:

placing the second relay in a first state to couple the neutral terminal of the first voltage input to a first output terminal of the second relay; and

placing the second relay in a second state couple the line terminal of the second voltage input to a second output terminal of the first relay.

16. The method of claim 15 , further comprising:

placing the third relay in a first state to couple the first output terminal of the first relay to the line output terminal of the voltage output; and

placing the third relay in a second state to couple the second output terminal of the first relay to the line output terminal of the voltage output.

17. The method of claim 15 , further comprising:

placing the fourth relay in a first state to couple the first output terminal of the second relay to the neutral output terminal of the voltage output; and

placing the fourth relay in a second state to couple the second output terminal of the second relay to the neutral output terminal of the voltage output.

18. The method of claim 15 , further comprising:

placing the third relay in a first state to couple the first output terminal of the first relay to the line output terminal of the voltage output; and

placing the third relay in a second state to couple the second output terminal of the second relay to the line output terminal of the voltage output.

19. The method of claim 15 , further comprising:

placing the fourth relay in a first state to couple the first output terminal of the second relay to the neutral output terminal of the voltage output; and

placing the fourth relay in a second state to couple the second output terminal of the first relay to the neutral output terminal of the voltage output.