LOAD CONTROL DEVICE FOR USE WITH LIGHTING CIRCUITS HAVING THREE-WAY SWITCHES

• US 20080024074A1
• Filed: 08/09/2007
• Published: 01/31/2008
• Est. Priority Date: 06/06/2005
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Steffie, Jamie, Blakeley, Matthew, Rogan, Christopher, Mosebrook, Donald
• Granted Patent: US 7,847,440 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 39/08 by shifting phase of trigger voltage applied to gas-filled controlling tubes also in controlled semiconductor devices in converters H02M5/00; with regulation G05F1/44
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: H05B 47/165 following a pre-assigned programmed sequence; Logic control [LC]
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A smart dimmer for control of a lighting load from an AC power source can replace any switch in a three-way or four-way lighting control system. The smart dimmer can be connected on the line-side or the load-side of a three-way system with a standard three-way switch in the other location. According to one embodiment of the present invention, the dimmer includes two triacs to control the intensity of the connected lighting load. The dimmer preferably includes two gate drive circuits coupled to the gates of the triacs for rendering the triacs conductive each half-cycle of the AC power source. The gate drive circuits include sensing circuits for detect whether the gates currents are flowing after the triacs are rendered conductive. A controller is operable to determine the state of the lighting load in response to whether the gate current is flowing or not flowing.

Claims

1. A load control device adapted to be coupled to a circuit including an AC power source, a load, and a single-pole double-throw three-way switch, the AC power source generating an AC line voltage for powering the load, the load control device comprising:

first, second, and third electrical load terminals;

a first controllably conductive device having a conductive state and a non-conductive state, the first controllably conductive device electrically coupled between the first load terminal and the second load terminal such that when the first controllably conductive device is in the conductive state and the load control device is coupled to the circuit, a load current is operable to flow between the first load terminal and the second load terminal, the first controllably conductive device having a first control input and operable to enter the conductive state in response to a first gate current conducted through the first control input;

a second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device electrically coupled between the first load terminal and the third load terminal such that when the second controllably conductive device is in the conductive state and the load control device is coupled to the circuit, the load current is operable to flow between the first load terminal and the third load terminal, the second controllably conductive device having a second control input and operable to enter the conductive state in response to a second gate current conducted through the second control input; and

a controller operable to control the first and second controllably conductive devices to control the load between an on state and an off state, the controller operable to drive the first controllably conductive device to change the first controllably conductive device from the non-conductive state to the conductive state each half-cycle of the AC line voltage, the controller operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load.

2. The load control device of claim 1, wherein the controller is further operable to drive the second controllably conductive device, such that the second controllably conductive device is operable to change from the non-conductive state to the conductive state, the controller operable to determine if the second controllably conductive device is presently conducting current to the load in response to the magnitude of the second gate current through the second control input of the second controllably conductive device.

3. The load control device of claim 2, further comprising:

a first sense circuit having an input operatively coupled to the control input of the first controllably conductive device and an output operatively coupled to the controller, the first sense circuit operable to provide a first control signal representative of the magnitude of the first gate current to the controller; and

a second sense circuit having an input operatively coupled to the control input of the second controllably conductive device and an output operatively coupled to the controller, the second sense circuit operable to provide a second control signal representative of the magnitude of the second gate current to the controller.

4. The load control device of claim 3, wherein the controller is operable to determine that the load is in the on state if one of the first and second gate currents has a magnitude of substantially zero amps.

5. The load control device of claim 4, wherein the controller is operable to determine that the load is in the off state if one of the first and second gate currents has a magnitude greater than substantially zero amps.

6. The load control device of claim 5, wherein the controller is operable to determine that the load is in the off state if the first gate current has a magnitude greater than substantially zero amps when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current has a magnitude greater than substantially zero amps when the controller is driving the second controllably conductive device.

7. The load control device of claim 6, wherein the controller is operable to determine that the load is in the off state if the first gate current has a magnitude greater than approximately one milliamp when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current has a magnitude greater than approximately one milliamp when the controller is driving the second controllably conductive device.

8. The load control device of claim 4, wherein the controller is operable to determine that the load is in the on state if the first gate current has a magnitude of substantially zero amps when the controller is driving the first controllably conductive device, and to determine that the load is in the on state if the second gate current has a magnitude of substantially zero amps when the controller is driving the second controllably conductive device.

9. The load control device of claim 3, further comprising:

a line voltage detect circuit operatively coupled to the first terminal to detect the presence of the AC line voltage at the first terminal.

10. The load control device of claim 9, wherein the controller is operable to determine that the load is in the off state if the AC line voltage is not present at the first terminal.

11. The load control device of claim 10, wherein the controller is operable to determine that the load is in the on state if one of the first and second gate currents has a magnitude of substantially zero amps.

12. The load control device of claim 9, further comprising:

a neutral terminal;

wherein the line voltage detect circuit is coupled between the first terminal and the neutral terminal.

13. The load control device of claim 3, wherein the first and second sense circuits comprise first and second current sense circuits.

14. The load control device of claim 13, further comprising:

a first trigger circuit coupled in series electrical connection with the first control input of the first controllably conductive device and the input of the first sense circuit; and

a second trigger circuit coupled in series electrical connection with the second control input of the second controllably conductive device and the input of the second sense circuit;

wherein the first and second trigger circuits are responsive to the controller.

15. The load control device of claim 14, wherein the first and second trigger circuits comprise opto-triacs.

16. The load control device of claim 13, wherein the first and second current sense circuits comprise opto-couplers.

17. The load control device of claim 3, wherein the controller is operable to determine that the load is in the on state if the first gate current is not flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device, and to determine that the load is in the on state if the second gate current is not flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device.

18. The load control device of claim 17, wherein the controller is operable to determine that the load is in the off state if the first gate current is flowing near the peak of the AC line voltage when the controller is driving the first controllably conductive device, and to determine that the load is in the off state if the second gate current is flowing near the peak of the AC line voltage when the controller is driving the second controllably conductive device.

19. The load control device of claim 3, wherein the controller is operable to drive the first controllably conductive device at a predetermined time each half-cycle, and to monitor the first control signal from the first sense circuit after a predetermined amount of time has expired since the first controllably conductive device was driven by the controller.

20. The load control device of claim 3, wherein the controller is operable to drive the first controllably conductive device at substantially the beginning of a half-cycle, and to monitor the first control signal from the first sense circuit during the half-cycle near a time corresponding to a peak voltage of the AC line voltage.

21. The load control device of claim 2, further comprising:

a neutral terminal;

wherein gate current is conducted through the neutral terminal.

22. The load control device of claim 21, further comprising:

a first zero-crossing detector coupled to between the second terminal and the neutral terminal; and

a second zero-crossing detector coupled to between the third terminal and the neutral terminal;

wherein the first gate current is conducted through the first zero-crossing detector to the neutral terminal, and the second gate current is conducted through the second zero-crossing detector to the neutral terminal.

23. The load control device of claim 21, further comprising:

a power supply coupled between the first terminal and the neutral terminal, the power supply operable to provide power to the controller.

24. The load control device of claim 2, wherein the first and second controllably conductive devices comprise bidirectional semiconductor switches.

25. The load control device of claim 24, wherein the bidirectional semiconductor switches comprise triacs.

26. The load control device of claim 2, further comprising:

a communication circuit adapted to transmit a message including feedback information representative of the states of the first and second controllably conductive devices and the outputs of the first and second sensing devices.

27. The load control device of claim 2, further comprising:

a visual display for providing feedback to a user of the load control device.

28. The load control device of claim 2, wherein the controller is operable to drive the first and second controllably conductive devices a complementary basis, such that when the first controllably conductive device is conductive, the second controllably conductive device is non-conductive, and when the second controllably conductive device is conductive, the first controllably conductive device is non-conductive.

29. A method for controlling a load in a circuit comprising a power source, the load, a load control device, and a single-pole double-throw three-way switch, the method comprising the steps of:

providing first, second, and third electrical load terminals on the dimmer switch;

electrically coupling a first controllably conductive device between the first load terminal and the second load terminal, the first controllably conductive device having a conductive state and a non-conductive, the first controllably conductive device arranged such that when the first controllably conductive device is in the conductive state, a load current is operable to flow between the first load terminal and the second load terminal, the first controllably conductive device having a first control input;

conducting a first gate current through the first control input to cause the first controllably conductive device to enter the conductive state;

electrically coupling a second controllably conductive device between the first load terminal and the third load terminal, the second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device arranged such that when the second controllably conductive device is in the conductive state, the load current is operable to flow between the first load terminal and the third load terminal, the second controllably conductive device having a second control input;

conducting a second gate current through the second control input to cause the second controllably conductive device to enter the conductive state;

monitoring the first and second gate currents; and

determining, in response to the step of monitoring the first and second gate currents, whether the respective controllably conductive device is presently conducting the current to the load.

30. The method of claim 29, wherein the step of monitoring further comprises monitoring the magnitudes of the first and second gate currents.

31. The method of claim 30, further comprising the steps of:

determining that the load is in the on state if the gate current presently has a magnitude of substantially zero amps.

32. The method of claim 31, further comprising the steps of:

determining that the load is in the off state if the gate current presently has a magnitude greater than substantially zero amps.

33. The method of claim 29, further comprising the steps of:

detecting the presence of a line voltage at the first terminal; and

determining that the load is in the off state in response to the step of detecting the presence of line voltage.

34. The method of claim 33, further comprising the steps of:

determining that the load is in the on state if the gate current presently has a magnitude of substantially zero amps.

35. The method of claim 29, wherein the step of conducting a first gate current comprises driving the first controllably conductive device at a predetermined time during a half-cycle, and the step of monitoring comprises monitoring the first control signal from the first sense circuit after a predetermined amount of time has expired since the step of driving the first controllably conductive device.

36. The method of claim 29, wherein the step of conducting a first gate current comprises driving the first controllably conductive device at substantially the beginning of a half-cycle, and the step of monitoring comprises monitoring the first control signal from the first sense circuit during the half-cycle near a time corresponding to a peak voltage of the AC line voltage.

37. The method of claim 29, further comprising the step of:

transmitting a message including feedback information representative of the states of the first and second controllably conductive devices, the sensed first electrical characteristic, and the sensed second electrical characteristic.

38. The method of claim 29, further comprising the step of:

providing feedback to a user of the dimmer switch via a visual display.

39. A load control system for controlling the amount of power delivered to an electrical load from an AC power source generating an AC line voltage, the load control system comprising:

a single-pole double-throw (SPDT) three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to either the power source or the load, the SPDT three-way switch having a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact; and

a load control device comprising;

a first load terminal adapted to be coupled to either the power source or the load to which the SPDT three-way switch is not coupled to;

a second load terminal coupled to the first fixed contact of the SPDT three-way switch;

a third load terminal coupled to the second fixed contact of the SPDT three-way switch;

a first controllably conductive device having a conductive state and a non-conductive state, the first controllably conductive device having a first control input and operable to enter the conductive state in response to a first gate current conducted through the first control input;

a second controllably conductive device having a conductive state and a non-conductive state, the second controllably conductive device having a second control input and operable to enter the conductive state in response to a second gate current conducted through the second control input; and

a controller operable to control the first and second controllably conductive devices, the controller operable to determine if the first controllably conductive device is presently conducting current to the load in response to the magnitude of the first gate current through the first control input of the first controllably conductive device;

wherein when the SPDT three-way switch is in the first state, the controller is operable to control the first controllably conductive device such that a load current is operable to flow through the second load terminal when the first controllably conductive device is in the conductive state, and when the SPDT three-way switch is in the second state, the controller is operable to control the first controllably conductive device such that the load current is operable to flow through the third load terminal when the controllably conductive device is in the conductive state; and

wherein the controller is operable to determine, in response to the magnitude of the first gate current through the first control input of the first controllably conductive device, whether the first controllably conductive device is presently conducting current to the load, the controller further operable to determine, in response to the magnitude of the second gate current through the second control input of the second controllably conductive device, whether the second controllably conductive device is presently conducting current to the load.