On-board charger housekeeping power supply with automatic source transition

1. A power supply system for providing uninterrupted low voltage electrical power to control circuitry in an electric or hybrid-electric vehicle, the system comprising:

a transformer configured to receive at least one of a low voltage input from a vehicle battery and a rectified AC high voltage input and convert one of the low voltage input and the rectified AC high voltage input to a low voltage output for use in powering the control circuitry, the transformer including a first primary side configured to receive the low voltage input from the vehicle battery and a second primary side configured to receive the rectified AC high voltage input;

a first controller coupled to the low voltage input for operating a first switching device associated with the first primary side of the transformer, the first controller being operational to drive the first switching device to regulate the low voltage output using energy from the low voltage input when the rectified AC high voltage input is absent;

a second controller connected to the rectified AC high voltage input for operating a second switching device associated with the second primary side of the transformer, when the rectified AC high voltage input is present, the second controller being operational to (a) drive the second switching device to regulate the low voltage output using energy from the rectified AC high voltage input and (b) deactivate the first controller using a switching signal; and

an opto-coupler in communication with the second controller for receiving the switching signal and transmitting the switching signal from the second primary side across an isolation boundary to the first controller on the first primary side.

2. The system of claim 1 , further comprising:

a monostable circuit electrically disposed between the opto-coupler and the first controller, the monostable circuit configured to receive the switching signal from the opto-coupler and transmit an output to the first controller based on the switching signal.

3. The system of claim 2 , wherein the monostable circuit is a retriggerable monostable digital circuit having one of two states based on the switching signal, the output from the monostable circuit being based on the one of two states.

4. The system of claim 3 , wherein the first controller is deactivated when the switching signal from the second controller, transmitted across the isolation boundary by the opto-coupler to the monostable circuit, is a trigger pulse.

5. The system of claim 1 , wherein the transformer is an isolated flyback transformer.

6. The system of claim 5 , wherein the first controller and the second controller are each flyback converter controllers.

7. The system of claim 1 , wherein the first switching device and the second switching device are MOSFETs.

8. The system of claim 1 , wherein the second controller has a setpoint less than a minimum value of the rectified AC high voltage input so that it is deactivated when the rectified AC high voltage input is absent.

9. A power supply system for providing uninterrupted low voltage electrical power to control circuitry in an electric or hybrid-electric vehicle, the system comprising:

a transformer having a first primary side configured to receive a low voltage input from a vehicle battery and a second primary side configured to receive a rectified AC high voltage input;

a first controller coupled to the low voltage input and operational to drive a first switching device to regulate a low voltage output using energy from the low voltage input when the rectified AC high voltage input is absent; and

a second controller connected to the rectified AC high voltage input and, when the rectified AC high voltage input is present, operational to (a) drive a second switching device to regulate the low voltage output using energy from the rectified AC high voltage input and (b) deactivate the first controller using a switching signal.

10. The system of claim 9 , further comprising:

an opto-coupler in communication with the second controller for receiving the switching signal and transmitting the switching signal from the second primary side across an isolation boundary to the first controller on the first primary side.

11. The system of claim 10 , further comprising:

a monostable circuit electrically disposed between the opto-coupler and the first controller, the monostable circuit configured to receive the switching signal from the opto-coupler and transmit an output to the first controller based on the switching signal.

12. The system of claim 11 , wherein the monostable circuit is a retriggerable monostable digital circuit having one of two states based on the switching signal, the output from the monostable circuit being based on the one of two states.

13. The system of claim 12 , wherein the first controller is deactivated when the switching signal from the second controller, transmitted across the isolation boundary by the opto-coupler to the monostable circuit, is a trigger pulse.

14. The system of claim 9 , wherein the transformer is an isolated flyback transformer.

15. The system of claim 14 , wherein the first controller and the second controller are each flyback converter controllers.

16. The system of claim 9 , wherein the first switching device and the second switching device are MOSFETs.

17. The system of claim 9 , wherein the second controller has a setpoint less than a minimum value of the rectified AC high voltage input so that it is deactivated when the rectified AC high voltage input is absent.

18. A method for providing uninterrupted low voltage electrical power to control circuitry in an electric or hybrid-electric vehicle, the method comprising:

receiving a low voltage input from a vehicle battery at a first primary side of a transformer;

converting the low voltage input to a low voltage output for use in powering the control circuitry;

receiving a rectified AC high voltage input at a second primary side of the transformer;

converting the rectified AC high voltage input to the low voltage output for use in powering the control circuitry when the rectified AC high voltage input is present; and

deactivating the first primary side of the transformer so that it stops converting the low voltage input to a low voltage output.

19. The method of claim 18 , further comprising:

activating a first controller to drive a first switching device to regulate the low voltage output using energy from the low voltage input when the rectified AC high voltage input is absent.

20. The method of claim 19 , wherein deactivating the first primary side of the transformer so that it stops converting the low voltage input to the low voltage output comprises:

transmitting a switching signal from a second controller across an isolation boundary to the first controller when the rectified AC high voltage input is present, the second controller connected to the rectified AC high voltage input for operating a second switching device associated with the second primary side of the transformer; and

deactivating the first controller in response to the switching signal so that it stops driving the first switching device.