Smart Electronic Switch for Low-Power Loads

• US 20100270982A1
• Filed: 03/31/2010
• Published: 10/28/2010
• Est. Priority Date: 04/24/2009
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Hausman, Donald F. JR., Yang, Bingrui, Salvestrini, Christopher James, Aguado Pelaez, Miguel
• Granted Patent: US 8,922,133 B2
• Time in Patent Office: Days
• US Class Current: 320/166
• CPC Class Codes: H01H 47/22 for supplying energising current for relay coil
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 5/293 using semiconductor devices only
• CPC Class Codes: H03K 17/6874 in a symmetrical configuration
• CPC Class Codes: H03K 17/79 controlling bipolar semiconductor switches with more than two PN-junctions, or more than three electrodes, or more than one electrode connected to the same conductivity region
• CPC Class Codes: H05B 39/081 by measuring the incident light H05B39/083 takes precedence
• CPC Class Codes: H05B 39/088 by wireless means, e.g. infrared transmitting means
• CPC Class Codes: H05B 47/105 in response to determined parameters
• CPC Class Codes: H05B 47/11 by determining the brightness or colour temperature of ambient light
• CPC Class Codes: H05B 47/115 by determining the presence or movement of objects or living beings
• CPC Class Codes: H05B 47/13 by using passive infrared detectors
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

A two-wire smart load control device, such as an electronic switch, for controlling the power delivered from a power source to an electrical load comprises a relay for conducting a load current through the load and an in-line power supply coupled in series with the relay for generating a supply voltage across a capacitor when the relay is conductive. The power supply controls when the capacitor charges asynchronously with respect to the frequency of the source. The capacitor conducts the load current for at least a portion of a line cycle of the source when the relay is conductive. The load control device also comprises a bidirectional semiconductor switch, which is controlled to minimize the inrush current conducted through the relay. The bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the capacitor of the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

Claims

1. A two-wire electronic switch adapted to be coupled between an AC power source and an electrical load for turning the electrical load on and off, the electronic switch comprising:

a controllably conductive device adapted to be coupled in series electrical connection between the source and the load, the controllably conductive device adapted to conduct a load current through the load when the controllably conductive device is conductive;

a controller operatively coupled the controllably conductive device for controlling the controllably conductive device to be conductive and non-conductive to turn the load on and off, respectively;

an output capacitor operable to develop to the DC supply voltage for powering the controller; and

an in-line power supply coupled in series with the controllably conductive device, the in-line power supply further coupled to the output capacitor for controlling when the output capacitor charges in order to generate the DC supply voltage across the output capacitor when the controllably conductive device is conductive, a voltage developed across the in-line power supply when the output capacitor is charging having a substantially small magnitude as compared to a peak voltage of an AC line voltage of the AC power source, the output capacitor adapted to conduct the load current for at least a portion of a line cycle of the AC power source when the controllably conductive device is conductive;

wherein the in-line power supply controls when the output capacitor charges asynchronously with respect to the frequency of the AC power source, such that the in-line power supply is operable to start and stop charging at any time during each half cycle, the power supply operable to start and to stop charging the output capacitor at least once during each half cycle of the AC power source.

2. The electronic switch of claim 1, wherein the controllably conductive device comprises a relay.

3. The electronic switch of claim 2, wherein the power supply comprises a first bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, such that the output capacitor is operable to charge when the relay is conductive and the first bidirectional semiconductor switch is non-conductive.

4. The electronic switch of claim 3, further comprising:

a second bidirectional semiconductor switch coupled in parallel with the series combination of the relay and the power supply, the controller operatively coupled to a control input of the first bidirectional semiconductor switch, the controller operable to turn on the load by first rendering the second bidirectional semiconductor switch conductive and then rendering the relay conductive, the controller operable to turn off the load by first rendering the relay non-conductive and then rendering the second bidirectional semiconductor switch non-conductive;

wherein the second bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the output capacitor of the power supply.

5. The electronic switch of claim 4, further comprising:

a drive circuit coupled between the controller and the control input of the first bidirectional semiconductor switch, the drive circuit operable to render the first bidirectional semiconductor switch conductive in response to a control signal provided by the controller.

6. The electronic switch of claim 5, wherein the power supply comprises a resistor coupled in series with the output capacitor, the resistor coupled to the drive circuit, such that the drive circuit is operable to render the first bidirectional semiconductor switch conductive in response to the current through the resistor exceeding a predetermined current threshold.

7. The electronic switch of claim 5, wherein the first bidirectional semiconductor switch comprises a triac.

8. The electronic switch of claim 3, wherein the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

9. The electronic switch of claim 8, wherein the controller provides a relay-set control signal to a SET coil of the relay for rendering the relay conductive, and provides a relay-reset control signal to a RESET coil of the relay for rendering the relay non-conductive, the power supply further comprising a thermistor responsive to a temperature of the power supply, the thermistor electrically coupled to the RESET coil of the relay for rendering the relay non-conductive in response to the over-temperature condition in the power supply.

10. The electronic switch of claim 9, wherein the thermistor comprises a PTC thermistor thermally coupled to the first bidirectional semiconductor switch of the power supply.

11. The electronic switch of claim 10, wherein the PTC thermistor is coupled in series electrical connection with the output capacitor of the power supply, the voltage across the series combination of the output capacitor and the PTC thermistor electrically coupled to the RESET coil of the relay, the controller is operable to control the relay-reset control signal to approximately circuit common to render the relay non-conductive in absence of the over-temperature condition in the power supply;

and

wherein the voltage across the series combination of the output capacitor and the PTC thermistor increases during the over-temperature condition in the power supply, such that the relay is rendered conductive independent of the magnitude of the relay-reset control signal.

12. The electronic switch of claim 3, wherein the power supply further comprises a control circuit coupled to the first bidirectional semiconductor switch for rendering the first bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to the magnitude of the DC supply voltage to render the first bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold.

13. The electronic switch of claim 12, wherein the control circuit of the power supply is operable to render the first bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold.

14. The electronic switch of claim 13, wherein the controller is operable to measure a charging time required to charge the output capacitor, and to determine if an overload condition is occurring if the length of the charging time is less than a predetermined charging time threshold.

15. The electronic switch of claim 12, wherein the controller is operable to determine when the magnitude of the DC supply voltage reaches the maximum DC supply voltage threshold, and to render the relay conductive and non-conductive immediately after the DC supply voltage reaches the maximum DC supply voltage threshold.

16. The electronic switch of claim 1, further comprising:

an off-state power supply coupled in parallel with the series combination of the relay and the in-line power supply, the off-state power supply coupled to the output capacitor for controlling when the output capacitor charges to generate the DC supply voltage across the output capacitor when the lighting load is off.

17. The electronic switch of claim 16, further comprising:

a communication circuit coupled to the controller, such that the controller is operable to turn the lighting load on and off in response to digital messages received via the communication circuit.

18. The electronic switch of claim 17, wherein the communication circuit comprises an RF transceiver.

19. The electronic switch of claim 16, wherein the off-state power supply comprises an isolated power supply.

20. The electronic switch of claim 1, further comprising:

a communication circuit coupled to the controller, such that the controller is operable to receive digital messages.

21. The electronic switch of claim 20, wherein the communication circuit comprises an RF transceiver.

22. The electronic switch of claim 20, wherein the communication circuit comprises an RF receiver.

23. The electronic switch of claim 20, wherein the communication circuit comprises an IR receiver.

24. The electronic switch of claim 1, further comprising:

an occupancy detection circuit for detecting the presence of an occupant in the space around the electronic switch;

wherein the controller is operable to turn the lighting load on in response to the occupancy detection circuit detecting the presence of the occupant.

25. The electronic switch of claim 1, wherein the output capacitor begins to charge when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold and stops charging when the magnitude of the DC supply voltage rises to a maximum DC supply voltage threshold.

26. The electronic switch of claim 1, wherein the in-line power supply does not comprise a transformer.

27. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:

a latching relay adapted to be coupled in series electrical connection between the source and the load, the latching relay adapted to conduct a load current through the load when the relay is conductive;

a controller operatively coupled to the relay for controlling the relay to be conductive and non-conductive to turn the load on and off, respectively;

an output capacitor operable to develop a DC supply voltage for powering the controller; and

an in-line power supply coupled in series with the relay, the in-line power supply further coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the output capacitor adapted to conduct the load current for at least a portion of a line cycle of the AC power source when the relay is conductive;

wherein the relay is rendered non-conductive in response to an over-temperature condition in the electronic switch.

28. The electronic switch of claim 27, wherein the power supply comprises a bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, such that the output capacitor is operable to charge when the relay is conductive and the bidirectional semiconductor switch is non-conductive.

29. The electronic switch of claim 28, wherein the controller provides a relay-set control signal to a SET coil of the relay for rendering the relay conductive, and provides a relay-reset control signal to a RESET coil of the relay for rendering the relay non-conductive, the power supply further comprising a thermistor responsive to a temperature of the power supply, the thermistor electrically coupled to the RESET coil of the relay for rendering the relay non-conductive in response to an over-temperature condition in the power supply.

30. The electronic switch of claim 29, wherein the thermistor comprises a PTC thermistor thermally coupled to the bidirectional semiconductor switch of the power supply.

31. The electronic switch of claim 30, wherein the PTC thermistor is coupled in series electrical connection with the output capacitor of the power supply, the voltage across the series combination of the output capacitor and the PTC thermistor electrically coupled to the RESET coil of the relay, the controller is operable to control the relay-reset control signal to approximately circuit common to render the relay non-conductive in absence of the over-temperature condition in the power supply;

and

wherein the voltage across the series combination of the output capacitor and the PTC thermistor increases during the over-temperature condition in the power supply, such that the relay is rendered conductive independent of the magnitude of the relay-reset control signal.

32. The electronic switch of claim 28, wherein the power supply further comprises a control circuit coupled to the bidirectional semiconductor switch for rendering the bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to the magnitude of the DC supply voltage to render the bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold

33. The electronic switch of claim 32, wherein the control circuit of the power supply is operable to render the bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold.

34. The electronic switch of claim 28, further comprising:

an off-state power supply coupled in parallel with the series combination of the relay and the in-line power supply, the off-state power supply coupled to the output capacitor for controlling when the output capacitor charges to generate the DC supply voltage across the output capacitor when the relay is non-conductive.

35. The electronic switch of claim 34, further comprising:

a communication circuit coupled to the controller, such that the controller is operable to turn the load on and off in response to digital messages received via the communication circuit.

36. The electronic switch of claim 27, wherein the bidirectional semiconductor switch of the power supply comprises two FETs in anti-series connection.

37. The electronic switch of claim 27, wherein a voltage developed across the power supply when the output capacitor is charging has a substantially small magnitude as compared to a peak voltage of an AC line voltage of the AC power source.

38. The electronic switch of claim 37, wherein the voltage developed across the power supply is approximately equal to the magnitude of the DC supply voltage when the output capacitor is charging.

39. The electronic switch of claim 27, further comprising:

a communication circuit coupled to the controller, such that the controller is operable to receive digital messages.

40. The electronic switch of claim 39, wherein the communication circuit comprises one of an RF transceiver, an RF receiver, and an IR receiver.

41. The electronic switch of claim 27, further comprising:

a triac coupled in parallel with the series combination of the relay and the power supply, the controller operatively coupled to a control input of the triac, the controller operable to turn on the load by first rendering the triac conductive and then rendering the relay conductive, the controller operable to turn off the load by first rendering the relay non-conductive and then rendering the triac non-conductive;

wherein the triac is rendered conductive in response to an over-current condition in the output capacitor of the power supply.

42. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:

a latching relay adapted to be coupled in series electrical connection between the source and the load for turning the load on and off;

a first bidirectional semiconductor switch coupled in parallel electrical connection with the relay, the first bidirectional semiconductor switch comprising a control input;

a controller operatively coupled to the relay and the control input of the first bidirectional semiconductor switch, the controller operable to turn on the load by first rendering the first bidirectional semiconductor switch conductive and then rendering the relay conductive, the controller operable to turn off the load by first rendering the relay non-conductive and then rendering the first bidirectional semiconductor switch non-conductive;

an output capacitor operable to develop a DC supply voltage for powering the controller; and

an in-line power supply coupled in series electrical connection with the relay, such that the first bidirectional semiconductor switch is coupled in parallel with the series combination of the relay and the power supply, the in-line power supply further coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the output capacitor adapted to conduct the load current for at least a portion of a line cycle of the AC power source when the relay is conductive;

wherein the first bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the output capacitor of the power supply.

43. The electronic switch of claim 42, wherein the power supply comprises a second bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, such that the output capacitor is operable to charge when the relay is conductive and the second bidirectional semiconductor switch is non-conductive.

44. The electronic switch of claim 43, further comprising:

a drive circuit coupled between the controller and the control input of the first bidirectional semiconductor switch, the drive circuit operable to render the first bidirectional semiconductor switch conductive in response to a control signal provided by the controller.

45. The electronic switch of claim 44, wherein the power supply comprises a resistor coupled in series with the output capacitor, the resistor coupled to the drive circuit, such that the drive circuit is operable to render the first bidirectional semiconductor switch conductive in response to the current through the resistor exceeding a predetermined current threshold.

46. The electronic switch of claim 44, wherein the first bidirectional semiconductor switch comprises a triac.

47. The electronic switch of claim 43, wherein the latching relay is coupled to the power supply, such that the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

48. The electronic switch of claim 47, wherein the controller provides a relay-set control signal to a SET coil of the relay for rendering the relay conductive, and provides a relay-reset control signal to a RESET coil of the relay for rendering the relay non-conductive, the power supply further comprising a PTC thermistor thermally coupled to the second bidirectional semiconductor switch of the power supply, the PTC thermistor coupled in series electrical connection with the output capacitor of the power supply, the voltage across the series combination of the output capacitor and the PTC thermistor electrically coupled to the RESET coil of the relay, the controller is operable to control the relay-reset control signal to approximately circuit common to render the relay non-conductive in absence of the over-temperature condition in the power supply;

and

wherein the voltage across the series combination of the output capacitor and the PTC thermistor increases during the over-temperature condition in the power supply, such that the relay is rendered conductive independent of the magnitude of the relay-reset control signal.

49. The electronic switch of claim 43, wherein the power supply further comprises a control circuit coupled to the second bidirectional semiconductor switch for rendering the second bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to the magnitude of the DC supply voltage to render the second bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold.

50. The electronic switch of claim 49, wherein the control circuit of the power supply is operable to render the second bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold.

51. The electronic switch of claim 42, wherein a voltage developed across the power supply when the output capacitor is charging has a substantially small magnitude as compared to a peak voltage of an AC line voltage of the AC power source.

52. The electronic switch of claim 51, wherein the voltage developed across the power supply is approximately equal to the magnitude of the DC supply voltage when the output capacitor is charging.

53. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:

a latching relay adapted to be coupled in series electrical connection between the source and the load for turning the load on and off;

a first bidirectional semiconductor switch coupled in parallel electrical connection with the relay, the first bidirectional semiconductor switch comprising a control input;

a controller operatively coupled to the relay and the control input of the first bidirectional semiconductor switch, the controller operable to turn on the load by first rendering the first bidirectional semiconductor switch conductive and then rendering the relay conductive, the controller operable to turn off the load by first rendering the relay non-conductive and then rendering the first bidirectional semiconductor switch non-conductive;

an output capacitor operable to develop a DC supply voltage for powering the controller; and

an in-line power supply coupled in series electrical connection with the relay, such that the first bidirectional semiconductor switch is coupled in parallel with the series combination of the relay and the power supply, the in-line power supply further coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the power supply comprising a second bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, such that the output capacitor is operable to charge when the relay is conductive and the second bidirectional semiconductor switch is non-conductive;

wherein the first bidirectional semiconductor switch is rendered conductive in response to an over-current condition in the output capacitor of the power supply, and the relay is rendered non-conductive in response to an over-temperature condition in the power supply.

54. A two-wire electronic switch for controlling the power delivered from an AC power source to an electrical load, the electronic switch comprising:

a latching relay adapted to be coupled in series electrical connection between the source and the load for turning the load on and off;

a controller operatively coupled to the relay for turning the load on and off;

an output capacitor operable to develop a DC supply voltage for powering the controller; and

an in-line power supply coupled in series electrical connection with the relay, the in-line power supply further coupled to the output capacitor for generating the DC supply voltage across the output capacitor when the relay is conductive, the power supply comprising a bidirectional semiconductor switch coupled in series with the relay and in parallel with the output capacitor, such that the output capacitor is operable to charge when the relay is conductive and the bidirectional semiconductor switch is non-conductive, the bidirectional semiconductor switch rendered conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold and rendered non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold, the output capacitor adapted to conduct the load current for at least a portion of a line cycle of the AC power source when the relay is conductive;

wherein the controller is operable to measure a charging time required to charge the output capacitor, and to determine if an overload condition is occurring if the length of the charging time is less than a predetermined charging time threshold.

55. A power supply for an electronic switch, the electronic switch comprising a controllably conductive device adapted to be coupled between an AC power source and an electrical load for turning the electrical load on and off, the power supply comprising:

an output capacitor operable to develop to a DC supply voltage;

a bidirectional semiconductor switch adapted to be coupled in series with the controllably conductive device and in parallel with the output capacitor, such that the output capacitor is operable to charge when the bidirectional semiconductor switch is non-conductive; and

a control circuit coupled to the bidirectional semiconductor switch for rendering the bidirectional semiconductor switch conductive and non-conductive, the control circuit responsive to the magnitude of the DC supply voltage to render the bidirectional semiconductor switch conductive when the magnitude of the DC supply voltage reaches a maximum DC supply voltage threshold and to render the bidirectional semiconductor switch non-conductive when the magnitude of the DC supply voltage drops to a minimum DC supply voltage threshold, a voltage developed across the power supply when the output capacitor is charging has a substantially small magnitude as compared to a peak voltage of an AC line voltage of the AC power source;

wherein the in-line power supply controls when the output capacitor charges asynchronously with respect to the frequency of the AC power source, such that the in-line power supply is to start and stop charging at any time during each half cycle, the power supply operable to start and to stop charging the output capacitor at least once during each half cycle of the AC power source.

56. The power supply of claim 55, wherein the voltage developed across the power supply is approximately equal to the magnitude of the DC supply voltage when the output capacitor is charging.

57. The power supply of claim 55, wherein the bidirectional semiconductor switch comprises two FETs in anti-series connection.