Method and apparatus for phase-controlling a load

1. A load control device for controlling an amount of power delivered from an alternating current (AC) power source to an electrical load, the load control device comprising:

a bidirectional semiconductor switch configured to be coupled between the AC power source and the electrical load; and

a controller operatively coupled to the bidirectional semiconductor switch, the controller configured to:

determine to operate the electrical load via a phase control signal in a forward phase-control mode;

after determining to operate the electrical load via the phase control signal in the forward phase-control mode, control the bidirectional semiconductor switch to provide the phase control signal in a reverse phase-control mode for a predetermined period of time to the electrical load to charge a bus capacitor of the electrical load;

after the predetermined period of time has elapsed, switch the phase control signal to the forward phase-control mode; and

control the bidirectional semiconductor switch to provide the phase control signal in the forward phase-control mode to the electrical load.

2. The load control device of claim 1 , wherein the predetermined period of time is approximately equal to a length of an AC line cycle of the AC power source.

3. The load control device of claim 1 , wherein a last line cycle of the phase control signal when operating in the reverse phase control mode and a first line cycle of the phase control signal when operating in the forward phase control mode have approximately the same conduction time.

4. The load control device of claim 1 , wherein a last line cycle of the phase control signal when operating in the reverse phase control mode and a first line cycle of the phase control signal when operating in the forward phase control mode have approximately the same RMS voltage value.

5. The load control device of claim 1 , wherein the amount of power delivered to the electrical load via a last line cycle of the phase control signal when operating in the reverse phase control mode is substantially equal to the amount of power delivered to the electrical load via a first line cycle of the phase control signal when operating in the forward phase control mode.

6. A method for controlling an amount of power delivered from an alternating current (AC) power source to an electrical load by a load control device, the method comprising:

determining to operate the electrical load with the load control device via a phase control signal in a forward phase-control mode;

after determining to operate the electrical load with the load control device via the phase control signal in the forward phase-control mode, providing the phase control signal in a reverse phase-control mode for a predetermined period of time to the electrical load to charge a bus capacitor of the electrical load;

after the predetermined period of time has elapsed, switching the phase control signal to the forward phase-control mode; and

providing the phase control signal in the forward phase-control mode to the electrical load.

7. The method of claim 6 , wherein the predetermined period of time is approximately equal to a length of an AC line cycle of the AC power source.

8. The method of claim 6 , wherein a last line cycle of the phase control signal when operating in the reverse phase control mode and a first line cycle of the phase control signal when operating in the forward phase control mode have approximately the same conduction time.

9. The method of claim 6 , wherein a last line cycle of the phase control signal when operating in the reverse phase control mode and a first line cycle of the phase control signal when operating in the forward phase control mode have approximately the same RMS voltage value.

10. The method of claim 6 , wherein the amount of power delivered to the electrical load via a last line cycle of the phase control signal when operating in the reverse phase control mode is substantially equal to the amount of power delivered to the electrical load via a first line cycle of the phase control signal when operating in the forward phase control mode.

11. A load control device for controlling an amount of power delivered from an alternating current (AC) power source to an electrical load, the load control device comprising:

a controller configured to:

operate in a reverse phase-control mode for a predetermined period of time; and

determine whether an over-current condition occurs during the predetermined period of time;

wherein, when the controller determines that the over-current condition has not occurred, the controller is configured to operate in a forward phase-control mode; and

wherein, when the controller determines that the over-current condition has occurred, the controller is configured to enter an over-current protection mode.

12. The load control device of claim 11 , wherein the over-current protection mode is characterized by the controller determining whether the over-current was caused by inrush current or a fault condition.

13. The load control device of claim 11 , wherein the over-current protection mode is characterized by the controller determining whether the over-current was caused by inrush current or a fault condition by measuring a rate of change of an output current signal.

14. The load control device of claim 13 , wherein the output current signal is representative of a magnitude of current flowing through a bidirectional semiconductor switch of the load control device.

15. The load control device of claim 11 , wherein the controller is configured to determine whether the over-current condition occurs by comparing an output current signal to a current threshold.

16. A load control device for controlling an amount of power delivered from an alternating current (AC) power source to an electrical load, the load control device comprising:

a controller configured to:

operate in a reverse phase-control mode for a predetermined period of time; and

determine whether an over-current condition occurs during the predetermined period of time;

wherein, when the controller determines that the over-current condition has not occurred, the controller is configured to determine a phase-control mode of operation; and

wherein, when the controller determines that the over-current condition has occurred, the controller is configured to determine whether the over-current was caused by inrush current or a fault condition.

17. The load control device of claim 15 , wherein the controller determines whether the over-current condition was caused by inrush current or a fault condition by measuring a rate of change of an output current signal.

18. The load control device of claim 17 , wherein the output current signal is representative of a magnitude of current flowing through a bidirectional semiconductor switch of the load control device.