Input overvoltage protection circuits for power supplies

1. An electrical power supply comprising:

a power converter comprising an input;

a protection circuit comprising:

an input;

a first current path coupled between the input of the protection circuit and the input of the power converter;

a second current path coupled between the input of the protection circuit and the input of the power converter;

a first switching device coupled in the first current path and controllable to turn on during startup of the power converter to provide a supply current along the first current path;

a second switching device coupled in the second current path; and

a control circuit configured to:

turn off the first switching device and turn on the second switching device to provide the supply current along the second current path in response to a power converter input voltage exceeding a first defined threshold and being less than a second defined threshold; and

turn off the second switching device in response to a protection circuit input voltage at the input of the protection circuit exceeding the second defined threshold.

2. The electrical power supply of claim 1 , wherein the first switching device is a self-biasing MOSFET configured to turn on in response to the protection circuit input voltage.

3. The electrical power supply of claim 1 , wherein the protection circuit input voltage is an AC input voltage, wherein the first defined threshold is a rated peak voltage of the AC input voltage, and wherein the second defined threshold is a voltage at least 120% of the rated peak voltage of the AC input voltage.

4. The electrical power supply of claim 1 , wherein the control circuit is configured to turn off the second switching device in response to the protection circuit input voltage at the input of the protection circuit exceeding the second defined threshold for a defined period of time.

5. The electrical power supply of claim 4 , wherein the defined period of time is based on the second defined threshold.

6. The electrical power supply of claim 1 , wherein the control circuit is configured to control the first switching device to turn on during startup of the power converter.

7. The electrical power supply of claim 1 , wherein the control circuit is further configured to:

sense the power converter input voltage; and

sense the protection circuit input voltage.

8. The electrical power supply of claim 7 , wherein the power converter input voltage is an output voltage of the protection circuit.

9. The electrical power supply of claim 1 , wherein the protection circuit further comprises a second transistor coupled to the first switching device and configured to limit current passing through the first switching device.

10. The electrical power supply of claim 1 , wherein the protection circuit further comprises a resistance serially coupled to the first switching device; and

wherein the second switching device is coupled in parallel with the first switching device and the resistance.

11. The electrical power supply of claim 1 , wherein the protection circuit is coupled to the power converter in a high-side rail.

12. The electrical power supply of claim 1 , wherein the protection circuit further comprises an auxiliary power supply coupled to a gate terminal of the first switching device and configured to provide a bias voltage to the gate terminal.

13. A method of controlling a power supply comprising:

turning on a first switching device of a protection circuit during a startup of a power converter to provide an output current to the power converter along a first current path of the protection circuit;

turning off the first switching device and turning on a second switching device of the protection circuit to provide the output current along a second current path of the protection circuit in response to an output voltage on an output of the protection circuit exceeding a first defined threshold and being less than a second defined threshold to provide the output current to the power converter along a second current path of the protection circuit; and

turning off the second switching device in response to an input voltage on an input of the protection circuit exceeding the second defined threshold to prohibit current flow to the power converter through the first and second switching devices.

14. The method of claim 13 , wherein the first switching device is a self-biasing switching device configured to turn on in response to an input voltage.

15. The method of claim 14 , wherein the input voltage is an AC input voltage, wherein the first defined threshold is a rated peak voltage of the AC input voltage, and wherein the second defined threshold is a voltage at least 120% of the rated peak voltage of the AC input voltage.

16. The method of claim 13 , wherein turning the first switching device on and off comprises controlling the first switching device via an opto-coupler coupled to the first switching device.

17. The method of claim 13 , wherein turning off the second switching device comprises turning off the second switching device in response to the input voltage exceeding the second defined threshold for a defined period of time.

18. The method of claim 13 further comprising limiting current passing from the input of the protection circuit to the power converter through the first switching device via a current limiting device coupled to the first switching device, the current limiting device comprising one of a resistance and a third switching device.

19. The method of claim 18 , further comprising bypassing the current limiting device via turning on the second switching device.

20. The method of claim 19 , wherein the first switching device is a MOSFET, and wherein the second switching device is a relay.