Controllable-load circuit for use with a load control device

1. A load control device for controlling power delivered from an AC power source to an electrical load, the load control device comprising:

a rectifier circuit configured to receive a phase-control voltage signal;

a load control circuit adapted to be coupled to the electrical load and configured to control the power delivered to the electrical load;

a control circuit coupled to the load control circuit and configured to control the load control circuit for controlling an amount of power delivered to the electrical load in response to a conduction period of the phase-control voltage signal; and

a controllable-load circuit configured to conduct a controllable-load current from the AC power source through the rectifier circuit, the controllable-load circuit configured to maintain a magnitude of the controllable-load current constant for at least a portion of each half-cycle of the AC power source;

wherein the control circuit is further configured to cause the controllable-load circuit to decrease the magnitude of the controllable-load current from an initial magnitude in a first half-cycle to a decreased magnitude in a second subsequent half-cycle, such that the conduction period of the phase-control voltage when the controllable-load current has the initial magnitude in the first half-cycle is the same as when the controllable-load current has the decreased magnitude in the second half-cycle.

2. The load control device of claim 1 , wherein the control circuit is further configured to monitor the conduction period of the phase-control voltage and to control the controllable-load circuit in response to the conduction period of the phase-control voltage.

3. The load control device of claim 2 , wherein the decreased magnitude is less than the initial magnitude and greater than approximately zero amps.

4. The load control device of claim 1 ,

wherein to decrease the magnitude of the controllable-load current from the initial magnitude in the first half-cycle to the decreased magnitude in the second subsequent half-cycle comprises to decrease the magnitude of the controllable-load current by a predetermined amount from the initial magnitude in the first half-cycle to the decreased magnitude in the second subsequent half-cycle; and

wherein the control circuit is further configured to:

monitor the conduction period of the phase-control voltage after the magnitude of the controllable-load current has been decreased to the decreased magnitude in the second subsequent half-cycle; and

subsequently decrease the magnitude of the controllable-load current by the predetermined amount in a third half-cycle when the conduction period of the phase-control voltage has not changed.

5. The load control device of claim 4 , wherein the control circuit is further configured to increase the magnitude of the controllable-load current by the predetermined amount in a fourth half-cycle when the conduction period of the phase-control voltage has changed.

6. The load control device of claim 4 , wherein the control circuit is further configured to:

incrementally decrease the magnitude of the controllable-load current by the predetermined amount until the magnitude of the controllable-load current is equal to a minimum magnitude; and

cease subsequent adjustment of the magnitude of the controllable-load current after the magnitude of the controllable-load current becomes equal to the minimum magnitude.

7. The load control device of claim 1 , wherein the control circuit is further configured to:

determine a total number of load control devices that receive the phase-control voltage; and

control the controllable-load circuit in response to the total number of load control devices.

8. The load control device of claim 7 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to determine the total number of load control devices by communicating a query message and receiving at least one query response message via the communication circuit.

9. The load control device of claim 7 , wherein the decreased magnitude of the controllable-load current is equal to a maximum magnitude divided by the total number of load control devices.

10. The load control device of claim 1 , wherein the control circuit is further configured to:

decrease the magnitude of the controllable-load current to a minimum magnitude; and

cease subsequent adjustment of the magnitude of the controllable-load current after the magnitude of the controllable-load current becomes equal to the minimum magnitude.

11. The load control device of claim 10 , wherein the minimum magnitude is approximately zero amps.

12. The load control device of claim 1 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to:

communicate a start-adjustment message via the communication circuit before decreasing the magnitude of the controllable-load current; and

communicate a stop-adjustment message via the communication circuit after decreasing the magnitude of the controllable-load current.

13. The load control device of claim 1 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to:

maintain the magnitude of the controllable-load current at the initial magnitude in response to receiving a start-adjustment message from another load control device via the communication circuit; and

decrease the magnitude of the controllable-load current from the initial magnitude to the decreased magnitude after receiving a stop-adjustment message from the other load control device.

14. A circuit for controlling power delivered from an AC power source to an electrical load, the circuit comprising:

a rectifier circuit configured to receive a phase-control voltage signal;

a controllable-load circuit configured to conduct a controllable-load current from the AC power source through the rectifier circuit, the controllable-load circuit further configured to maintain a magnitude of the controllable-load current constant for at least a portion of each half-cycle of the AC power source; and

a control circuit configured to adjust, from one half-cycle to the next, the magnitude at which the controllable-load current is held constant during the at least portion of each half-cycle of the AC power source;

wherein the control circuit is further configured to monitor a conduction period of the phase-control voltage and cause the controllable-load circuit to decrease the magnitude of the controllable-load current from an initial magnitude in a first half-cycle to a decreased magnitude in a second subsequent half-cycle, such that the conduction period of the phase-control voltage when the controllable-load current has the initial magnitude in the first half-cycle is the same as when the controllable-load current has the decreased magnitude in the second subsequent half-cycle.

15. The circuit of claim 14 , wherein the decreased magnitude is less than the initial magnitude and greater than approximately zero amps.

16. The circuit of claim 14 ,

wherein to decrease the magnitude of the controllable-load current from the initial magnitude in the first half-cycle to the decreased magnitude in the second subsequent half-cycle comprises to decrease the magnitude of the controllable-load current by a predetermined amount from the initial magnitude in the first half-cycle to the decreased magnitude in the second subsequent half-cycle; and

wherein the control circuit is further configured to:

monitor the conduction period of the phase-control voltage after the magnitude of the controllable-load current has been decreased to the decreased magnitude in the second subsequent half-cycle; and

subsequently decrease the magnitude of the controllable-load current by the predetermined amount in a third half-cycle when the conduction period of the phase-control voltage has not changed.

17. The circuit of claim 16 , wherein the control circuit is further configured to increase the magnitude of the controllable-load current by the predetermined amount in a fourth half-cycle when the conduction period of the phase-control voltage has changed.

18. The circuit of claim 16 , wherein the control circuit is further configured to decrease the magnitude of the controllable-load current to approximately zero amps.

19. The circuit of claim 18 , wherein the control circuit is further configured to:

monitor the conduction period of the phase-control voltage after the magnitude of the controllable-load current has been decreased to approximately zero amps; and

increase the magnitude of the controllable-load current in a subsequent half-cycle when the conduction period of the phase-control voltage has changed.

20. A circuit for controlling power delivered from an AC power source to an electrical load, the circuit comprising:

a rectifier circuit configured to receive a phase-control voltage signal;

a controllable-load circuit configured to conduct a controllable-load current from the AC power source through the rectifier circuit, the controllable-load circuit further configured to maintain a magnitude of the controllable-load current constant for at least a portion of each half-cycle of the AC power source; and

a control circuit configured to adjust, from one half-cycle to the next, the magnitude at which the controllable-load current is held constant during the at least portion of each half-cycle of the AC power source;

wherein the control circuit is further configured to cause the controllable-load circuit to decrease the magnitude of the controllable-load current from an initial magnitude in a first half-cycle to a decreased magnitude in a second subsequent half-cycle, such that the conduction period of the phase-control voltage when the controllable-load current has the initial magnitude in the first half-cycle is the same as when the controllable-load current has the decreased magnitude in the second subsequent half-cycle.

21. The circuit of claim 20 , wherein the control circuit is further configured to:

determine a total number of devices that receive the phase-control voltage; and

control the controllable-load circuit in response to the total number of devices.

22. The circuit of claim 21 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to determine the total number of devices by communicating a query message and receiving at least one query response message via the communication circuit.

23. The circuit of claim 21 , wherein the decreased magnitude of the controllable-load current is equal to a maximum magnitude divided by the total number of devices.

24. The circuit of claim 20 , wherein the control circuit is further configured to:

decrease the magnitude of the controllable-load current to a minimum magnitude; and

cease subsequent adjustment of the magnitude of the controllable-load current after the magnitude of the controllable-load current becomes equal to the minimum magnitude.

25. The circuit of claim 20 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to:

communicate a start-adjustment message via the communication circuit before decreasing the magnitude of the controllable-load current; and

communicate a stop-adjustment message via the communication circuit after decreasing the magnitude of the controllable-load current.

26. The circuit of claim 20 , further comprising a communication circuit configured to communicate messages; and

wherein the control circuit is further configured to:

maintain the magnitude of the controllable-load current at the initial magnitude in response to receiving a start-adjustment message from a device via the communication circuit; and

decrease the magnitude of the controllable-load current from the initial magnitude to the decreased magnitude after receiving a stop-adjustment message from the device.