Redundant DC input power supplies having back-feed protection

1. An electric power supply comprising:

a first input circuit for receiving a first input DC voltage;

a second input circuit for receiving a second input DC voltage, the second input circuit coupled to the first input circuit; and

a control circuit coupled to the first and second input circuits, the control circuit configured to:

sense the first input DC voltage and the second input DC voltage;

enable the first input circuit in response to the first input circuit having the highest input DC voltage;

disable the second input circuit in response to the first input circuit having the highest input DC voltage to substantially prevent current from back feeding to the first input circuit from the second input circuit;

enable the second input circuit in response to the second input circuit having the highest input DC voltage; and

disable the first input circuit in response to the second input circuit having the highest input DC voltage to substantially prevent current from back feeding to the second input circuit from the first input circuit.

2. The electric power supply of claim 1 , wherein:

the first input circuit comprises:

a positive rail;

a reference rail, wherein the positive and reference rails of the first input circuit define an input for receiving the first input DC voltage; and

a first set of switching devices coupled in series in the positive rail of the first input circuit; and

the second input circuit comprises:

a positive rail;

a reference rail, wherein the positive and reference rails of the second input circuit define an input for receiving the second input DC voltage; and

a first set of switching devices coupled in series in the positive rail of the second input circuit.

3. The electric power supply of claim 2 , wherein the first input circuit further comprises a second set of switching devices coupled in series in the reference rail of the first input circuit; and

wherein the second input circuit further comprises a second set of switching devices coupled in series in the reference rail of the second input circuit.

4. The electric power supply of claim 3 , wherein the control circuit includes a set of drivers coupled for controlling the plurality of first switching devices;

wherein one driver of the set of drivers is configured to control one switching device of the first set of switching devices of the first input circuit and one switching device of the second set of switching devices of the first input circuit; and

wherein another driver of the set of drivers is configured to control another switching device of the first set of switching devices of the first input circuit and another switching device of the second set of switching devices of the first input circuit.

5. The electric power supply of claim 2 , wherein the control circuit is configured to generate a first set of drive signals; and

wherein the control circuit includes a first set of drivers coupled for controlling the plurality of first switching devices based on the first set of drive signals.

6. The electric power supply of claim 5 , wherein the control circuit is configured to:

generate a signal for enabling the first set of drivers associated with the one of the first input circuit and the second input circuit having the highest input DC voltage; and

generate a signal for disabling the first set of drivers associated with the other one of the first input circuit and the second input circuit having the lowest input DC voltage.

7. The electric power supply of claim 2 , wherein one of:

the first set of switching devices of the first input circuit includes at least two MOSFETs; and

the first set of switching devices of the second input circuit includes at least two MOSFETs.

8. The electric power supply of claim 7 , wherein one of:

the first set of switching devices of the first input circuit includes at least one diode; and

the first set of switching devices of the second input circuit includes at least one diode.

9. A back-feed protection circuit for coupling to a power conversion circuit, the back-feed protection circuit comprising:

a first input circuit including:

a positive rail; and

a plurality of first MOSFETs including a first set of MOSFETs coupled to the positive rail of the first input circuit;

a second input circuit including:

a positive rail; and

a plurality of second MOSFETs including a first set of MOSFETs coupled to the positive rail of the second input circuit; and

a control circuit coupled to the first input circuit and the second input circuit for controlling the plurality of first MOSFETs and the plurality of second MOSFETs, the control circuit configured to:

enable the first input circuit or the second input circuit by turning on the plurality of first MOSFETs or the plurality of second MOSFETs; and

disable the other one of the first input circuit and the second input circuit to substantially prevent current from back feeding to the first input circuit and/or the second input circuit.

10. The back-feed protection circuit of claim 9 , wherein the first input circuit includes an input for receiving a first input DC voltage, wherein the second input circuit includes an input for receiving a second input DC voltage, and wherein the control circuit is configured to sense the first input DC voltage and the second input DC voltage and enable the one of the first input circuit and the second input circuit having the highest input DC voltage.

11. The back-feed protection circuit of claim 10 , wherein the control circuit is configured to generate a first set of drive signals and a second set of drive signals, and wherein the control circuit includes:

a first set of drivers coupled for controlling the plurality of first MOSFETs based on the first set of drive signals; and

a second set of drivers coupled for controlling the plurality of second MOSFETs based on the second set of drive signals.

12. The back-feed protection circuit of claim 11 , wherein the first set of drivers includes:

a first driver configured to control one MOSFET of the first set of MOSFETs; and

a second driver configured to control another MOSFET of the first set of MOSFETs.

13. The back-feed protection circuit of claim 11 , wherein the control circuit is configured to generate a signal for enabling the first set of drivers or the second set of drivers associated with the one of the first input circuit and the second input circuit having the highest input DC voltage, and a signal for disabling the first set of drivers or the second set of drivers associated with the other one of the first input circuit and the second input circuit.

14. The back-feed protection circuit of claim 13 , wherein the control circuit is configured to:

disable the first set of drivers in response to a drive signal of the second set of drive signals changing state; and

disable the second set of drivers in response to a drive signal of the first set of drive signals changing state.

15. The back-feed protection circuit of claim 9 wherein the first input circuit includes a diode coupled to the first set of MOSFETs and another diode coupled to the second set of MOSFETs.

16. A method of manufacturing a back-feed protection circuit comprising:

coupling a first input circuit to a second input circuit, wherein:

the first input circuit comprises an input for receiving a first input DC voltage; and

the second input circuit comprises an input for receiving a second input DC voltage; and

coupling a control circuit to the first and second input circuits, the control circuit configured to:

sense the first input DC voltage and the second input DC voltage;

enable one of the first input circuit and the second input circuit having the highest input DC voltage; and

disable the other one of the first input circuit and the second input circuit to substantially prevent current from back feeding to the first input circuit and/or the second input circuit.

17. The method of claim 16 , further comprising:

coupling a first set of switching devices in series in a positive rail of the first input circuit; and

coupling a second set of switching devices in series in a positive rail of the second input circuit.

18. The method of claim 17 , wherein coupling the first set of switching devices comprises coupling at least two MOSFETs and at least one diode to the positive rail of the first input circuit; and

wherein coupling the second set of switching devices comprises coupling at least two MOSFETs and at least one diode to the positive rail of the second input circuit.

19. The method of claim 17 , further comprising:

coupling a first set of drivers to the first set of switching devices of the first input circuit; and

coupling a second set of drivers to the second set of switching devices of the second input circuit;

wherein the control circuit is configured to:

generate a signal for enabling the first set of drivers or the second set of drivers associated with the one of the first input circuit and the second input circuit having the highest input DC voltage; and

generate a signal for disabling the first set of drivers or the second set of drivers associated with the other one of the first input circuit and the second input circuit.

20. The method of claim 19 , further comprising:

coupling a third set of switching devices in series in a reference rail of the first input circuit;

coupling a third set of drivers to the third set of switching devices of the first input circuit;

coupling a fourth set of switching devices in series in a reference rail of the second input circuit; and

coupling a fourth set of drivers to the fourth set of switching devices of the second input circuit.