Load control device having a controllable filter circuit

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 first terminal adapted to be coupled to the AC power source;

a second terminal adapted to be coupled to the electrical load;

a bidirectional semiconductor switch coupled in series between the first terminal and the second terminal, the bidirectional semiconductor switch configured to be controlled to a conductive state and a non-conductive state;

a filter circuit coupled between the first terminal and the second terminal, the filter circuit comprising a first capacitor and an inductor coupled in series between the bidirectional semiconductor switch and the second terminal, the filter circuit further comprising a controllable switch; and

a control circuit configured to render the bidirectional semiconductor switch conductive and non-conductive to control the amount of power delivered to the electrical load, the control circuit further configured to adjust an impedance of the filter circuit;

wherein the control circuit is configured to render the controllable switch conductive and non-conductive to respectively connect and disconnect the first capacitor from series connection between the first terminal and the second terminal to adjust the impedance of the filter circuit.

2. The load control device of claim 1 , wherein the filter circuit further comprises a second capacitor in series connection between the first terminal and the second terminal, the first capacitor and the second capacitor coupled in parallel between the first terminal and the second terminal.

3. The load control device of claim 2 , wherein the control circuit is configured to render the controllable switch non-conductive to control a capacitance between the first terminal and the second terminal to a first value by coupling only the second capacitor between the first terminal and the second terminal, and render the controllable switch conductive to increase the capacitance between the first terminal and the second terminal to a second value by coupling the first capacitor and the second capacitor in parallel between the first terminal and the second terminal.

4. The load control device of claim 2 , wherein the control circuit is configured to render the controllable switch non-conductive when the electrical load is in an off state, and render the controllable switch conductive when the electrical load is in an on state.

5. The load control device of claim 2 , wherein the first capacitor is coupled in parallel with the second capacitor and the controllable switch.

6. The load control device of claim 1 , further comprising:

an air-gap switch;

wherein the control circuit is configured to render the controllable switch conductive at the end of a turn-on period after the air-gap switch is closed to turn on the electrical load.

7. The load control device of claim 6 , wherein the control circuit comprises a delay circuit to render the controllable switch conductive at the end of the turn-on period, and the turn-on period comprises a predetermined number of line cycles of the AC power source.

8. The load control device of claim 1 , wherein the electrical load comprises a lighting load, and the control circuit is configured to control the controllable switch of the controllable filter based on a target intensity of the lighting load.

9. The load control device of claim 1 , wherein the control circuit is configured to adjust the impedance of the filter circuit based on the state of the bidirectional semiconductor switch.

10. The load control device of claim 1 , wherein the control circuit is configured to adjust the impedance of the filter circuit during a turn-on period after the load control device receives an input to turn on the electrical load.

11. The load control device of claim 1 , wherein the control circuit is configured to adjust the impedance of the filter circuit based on the amount of power delivered to the electrical load.

12. The load control device of claim 1 , further comprising:

an actuator configured to receive a user input;

wherein the control circuit is configured to enter an advanced programming mode, and adjust the impedance of the filter circuit in response to an actuation of the actuator when in the advanced programming mode.

13. 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 first terminal adapted to be coupled to the AC power source;

a second terminal adapted to be coupled to the electrical load;

a bidirectional semiconductor switch coupled in series between the first terminal and the second terminal, the bidirectional semiconductor switch configured to be controlled to a conductive state and a non-conductive state;

a filter circuit coupled between the first terminal and the second terminal, the filter circuit comprising a first capacitor, a resistor, and an inductor coupled in series between the bidirectional semiconductor switch and the second terminal, the filter circuit further comprising a first controllable switch and a second controllable switch; and

a control circuit configured to render the bidirectional semiconductor switch conductive and non-conductive to control the amount of power delivered to the electrical load, the control circuit further configured to adjust an impedance of the filter circuit;

wherein the resistor and the first controllable switch are coupled in parallel between the first terminal and the second terminal, and the first capacitor and the second controllable switch are coupled in series between the first terminal and the second terminal;

wherein the control circuit is configured to render the first controllable switch conductive and non-conductive to respectively disconnect and connect the resistor from the series connection between the first terminal and the second terminal to adjust the impedance of the filter circuit; and

wherein the control circuit is configured to render the second controllable switch conductive and non-conductive to respectively connect and disconnect the first capacitor from series connection between the first terminal and the second terminal to adjust the impedance of the filter circuit.

14. The load control device of claim 13 , wherein the filter circuit further comprises a second capacitor in series connection between the first terminal and the second terminal, the first capacitor and the second capacitor coupled in parallel between the first terminal and the second terminal.

15. The load control device of claim 14 , wherein the control circuit is configured to render the second controllable switch non-conductive to control a capacitance between the first terminal and the second terminal to a first value by coupling only the second capacitor between the first terminal and the second terminal, and render the second controllable switch conductive to increase the capacitance between the first terminal and the second terminal to a second value by coupling the first capacitor and the second capacitor in parallel between the first terminal and the second terminal.

16. The load control device of claim 13 , wherein the control circuit is configured to render the first controllable switch conductive and the second controllable switch non-conductive when the electrical load is in an off state, and render the first controllable switch non-conductive and the second controllable switch conductive when the electrical load is in an on state.

17. 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 first terminal adapted to be coupled to the AC power source;

a second terminal adapted to be coupled to the electrical load;

a bidirectional semiconductor switch coupled in series between the first terminal and the second terminal, the bidirectional semiconductor switch configured to be controlled to a conductive state and a non-conductive state;

a filter circuit coupled between the first terminal and the second terminal;

a control circuit configured to render the bidirectional semiconductor switch conductive and non-conductive to control the amount of power delivered to the electrical load, the control circuit further configured to adjust an impedance of the filter circuit; and

a measurement circuit configured to generate a feedback signal indicating a magnitude of a voltage developed across the load control device;

wherein the control circuit is configured to measure a slope of the feedback signal when the bidirectional semiconductor switch is transitioning from the non-conductive state to the conductive state, and adjust the impedance of the filter circuit in response to the slope of the feedback signal.

18. The load control device of claim 17 , wherein the control circuit is configured to increase a capacitance of the filter circuit between the first terminal and the second terminal when the slope exceeds a predetermined threshold.

19. The load control device of claim 17 , wherein the control circuit is configured to measure the slope of the feedback signal and subsequently adjust the impedance of the filter circuit in response to the slope of the feedback signal during a start-up routine when the control circuit is powered on.

20. The load control device of claim 17 , wherein the filter circuit is further coupled between the bidirectional semiconductor switch and the second terminal.