Load control device having a variable drive circuit

• US 20070236152A1
• Filed: 04/10/2006
• Published: 10/11/2007
• Est. Priority Date: 04/10/2006
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Orchowski, Neil, Davis, Gregory, Hausman, Donald
• Granted Patent: US 7,619,365 B2
• Time in Patent Office: Days
• US Class Current: 315/209.R
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 5/293 using semiconductor devices only
• CPC Class Codes: H03K 2217/0009 AC switches, i.e. delivering AC power to a load
• CPC Class Codes: H05B 39/048 with reverse phase control
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A load control device for controlling the amount of power delivered to an electrical load from a source of AC power comprises a controllably conductive device and a variable gate drive circuit. The controllably conductive device is coupled in series electrical connection between the source and the electrical load to control the amount of power delivered to the load. The variable drive circuit is thermally coupled to the controllably conductive device and provides a continuously variable impedance in series with the control input of the controllably conductive device. The impedance of the variable drive circuit is operable to decrease as a temperature of the controllably conductive device increases and vice versa. Preferably, the variable drive circuit comprises an NTC thermistor. Accordingly, the switching times of the controllably conductive device, i.e., the times when the controllably conductive device is changing between the conductive and non-conductive states, remain constant, or alternatively decrease, as the temperature of the controllably conductive device increases.

Claims

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

a controllably conductive device adapted to be coupled in series electrical connection between the source and the electrical load, the controllably conductive device having a control input to render the controllably conductive device conductive and non-conductive; and

a variable drive circuit coupled to the control input of the controllably conductive device to provide an impedance in series with the control input of the controllably conductive device;

wherein the variable drive circuit is operable to control the impedance in response to a temperature of the controllably conductive device.

2. The load control device of claim 1, wherein the variable drive circuit is operable to decrease the impedance as the temperature of the controllably conductive device increases and operable to increase as the temperature of the controllably conductive device decreases.

3. The load control device of claim 2, wherein the variable drive circuit is operable to provide a continuously variable impedance in series with the control input of the controllably conductive device.

4. The load control device of claim 3, wherein the variable drive circuit is thermally coupled to the controllably conductive device.

5. The load control device of claim 4, wherein the variable drive circuit comprises a thermistor.

6. The load control device of claim 5, wherein the thermistor comprises an NTC thermistor.

7. The load control device of claim 6, wherein the variable drive circuit further comprises a first resistor coupled in series electrical connection with the control input of the controllably conductive device and in parallel electrical connection with the NTC thermistor.

8. The load control device of claim 7, wherein the variable drive circuit further comprises a second resistor coupled in series electrical connection with the NTC thermistor;

wherein the series combination of the second resistor and the NTC thermistor is coupled in parallel electrical connection with the first resistor.

9. The load control device of claim 3, wherein the controllably conductive device comprises a semiconductor switch.

10. The load control device of claim 9, wherein the semiconductor switch comprises a first FET and a second FET in anti-series connection.

11. The load control device of claim 10, wherein the first FET and the second FET are independently controlled.

12. The load control device of claim 11, wherein the variable gate drive circuit comprises a first variable gate drive circuit in series electrical connection with the first FET, and a second variable gate drive circuit in series electrical connection with the second FET.

13. The load control device of claim 10, wherein a gate of the first FET is electrically connected to a gate of the second FET.

14. The load control device of claim 9, wherein the semiconductor switch comprises a FET in a bridge rectifier.

15. The load control device of claim 9, wherein the semiconductor switch comprises two IGBTs in anti-series connection.

16. The load control device of claim 9, wherein the semiconductor switch comprises an IGBT in a bridge rectifier.

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

a control circuit coupled to the variable gate drive circuit for providing a control signal for rendering the controllably conductive device conductive and nonconductive.

18. The load control device of claim 2, wherein the variable drive circuit is operable to provide at least three discrete steps of impedance in series with the control input of the controllably conductive device.

19. The load control device of claim 18, wherein the variable drive circuit is operable to provide at least ten discrete steps of impedance in series with the control input of the controllably conductive device.

20. The load control device of claim 2, wherein the electrical load comprises a lighting load and the variable drive circuit is operable to provide a plurality of discrete steps of impedance in series with the control input of the controllably conductive device such that the plurality of discrete steps of impedance is great enough to prevent perceptible flicker in the lighting load as the impedances are changed from one step to the next.

21. A load control device, for controlling the amount of power delivered to an electrical load from a source of AC power, comprising:

a controllably conductive device adapted to be coupled in series electrical connection between the source and the electrical load, the controllably conductive device having a control input for changing the controllably conductive device between a conductive state and a non-conductive state, the controllably conductive device characterized by a switching time when the controllably conductive device is changing between the conductive state and the non-conductive state; and

a drive circuit coupled to the control input of the controllably conductive device and operable to control the duration of the switching time is responsive to a temperature of the controllably conductive device.

22. The load control device of claim 21, wherein the duration of the switching time remains substantially constant as the temperature of the controllably conductive device increases.

23. The load control device of claim 22, wherein the controllably conductive device is characterized by a nominal switching time and the switching time changes by less than 10% of the nominal switching time.

24. The load control device of claim 21, wherein the drive circuit is operable to produce a step change in the switching time, the step change less than approximately 20 μ

sec.

25. The load control device of claim 24, wherein the step change is less than approximately 10 μ

sec.

26. The load control device of claim 21, wherein the duration of the switching time decreases as the temperature of the controllably conductive device increases.

27. A drive circuit for a controllably conductive device in a load control device, the drive circuit comprising:

a first resistor operable to be coupled in series electrical connection with a control input of the controllably conductive device; and

a thermally sensitive device coupled in parallel electrical connection with the first resistor and thermally coupled to the controllably conductive device, the thermally sensitive device operable to provide a variable impedance responsive to a temperature of the controllably conductive device.

28. The drive circuit of claim 27, wherein the variable impedance decreases as the temperature of the controllably conductive device increases and increases as the temperature of the controllably conductive device decreases.

29. The drive circuit of claim 28, wherein the variable impedance changes continuously in response to changes in the temperature of the controllably conductive device.

30. The drive circuit of claim 29, wherein the thermally sensitive device comprises a thermistor.

31. The drive circuit of claim 30, wherein the thermistor comprises an NTC thermistor.

32. The drive circuit of claim 29, further comprising:

a second resistor coupled in series electrical connection with the thermally sensitive device.

33. The drive circuit of claim 27, wherein the variable impedance comprises at least three discrete steps of impedance in series electrical connection with the control input of the controllably conductive device in response to the temperature of the controllably conductive device.

34. The drive circuit of claim 33, wherein the variable impedance comprises at least ten discrete steps of impedance in series electrical connection with the control input of the controllably conductive device in response to the temperature of the controllably conductive device.

35. The drive circuit of claim 27, wherein the load control device is operable to control a lighting load, and the variable impedance comprises a plurality of discrete steps of impedance in series electrical connection with the control input of the controllably conductive device such that the plurality of discrete steps of impedance is great enough to prevent perceptible flicker in the lighting load as the variable impedance changes from one discrete step to the next discrete step.

36. A method for controlling a controllably conductive device in a load control device, the method comprising the steps of:

providing a variable impedance in series electrical connection with a control input of the controllably conductive device; and

controlling the variable impedance in response to the temperature of the controllably conductive device.

37. The method of claim 36, wherein the step of changing comprises decreasing the variable impedance as the temperature of the controllably conductive device increases and increasing the variable impedance as the temperature of the controllably conductive device decreases.

38. The method of claim 37, wherein the step of changing comprises changing the variable impedance continuously as the temperature of the controllably conductive device changes.

39. The method of claim 38, wherein the variable impedance comprises a thermistor.

40. The method of claim 39, wherein the thermistor comprises an NTC thermistor.

41. The method of claim 37, wherein the step of changing comprises providing at least three discrete steps of impedance for the variable impedance as the temperature of the controllably conductive device changes.

42. The method of claim 41, wherein the step of changing comprises providing at least ten discrete steps of impedance for the variable impedance as the temperature of the controllably conductive device changes.

43. The method of claim 37, wherein the load control device is operable to control a lighting load, and the step of changing comprises providing a plurality of discrete steps of impedance in series electrical connection with the control input of the controllably conductive device such that the plurality of discrete steps of impedance is great enough to prevent perceptible flicker in the lighting load as the variable impedance is changed from one discrete impedance step to the next discrete impedance step.

44. A method of controlling a controllably conductive device in a load control device, the method comprising the step of:

controlling the controllably conductive device between a conductive state and a non-conductive state for a switching time, the switching time responsive to a temperature of the controllably conductive device.

45. The method of claim 44, wherein the switching time remains substantially constant as the temperature of the controllably conductive device increases.

46. The method of claim 45, wherein the controllably conductive device is characterized by a nominal switching time and the switching time changes by less than 10% of the nominal switching time.

47. The method of claim 44, wherein the switching time changes in discrete steps of less than approximately 20 μ

sec each.

48. The method of claim 47, wherein the switching time changes in discrete steps of less than approximately 10 μ

sec each.

49. The method of claim 44, wherein the switching time decreases as the temperature of the controllably conductive device increases.

50. A load control device, for controlling the amount of power delivered to an electrical load from a source of AC power, comprising:

a controllably conductive device adapted to be coupled in series electrical connection between the source and the electrical load, the controllably conductive device having a control input for rendering the controllably conductive device conductive and non-conductive; and

a variable drive circuit coupled to the control input of the controllably conductive device for providing a continuously variable impedance in series with the control input of the controllably conductive device;

wherein the variable drive circuit is thermally coupled to the controllably conductive device such that the continuously variable impedance is operable to decrease as a temperature of the controllably conductive device increases and operable to increase as the temperature of the controllably conductive device decreases.

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

a first controllably conductive device operable to conduct current from the source to the load during a positive half-cycle of the AC power source, the first controllably conductive device having a first control input to render the first controllably conductive device conductive and non-conductive;

a second controllably conductive device operable to conduct current from the source to the load during a negative half-cycle of the AC power source, the second controllably conductive device having a second control input to render the second controllably conductive device conductive and non-conductive;

a control circuit operable to independently render the first and second controllably conductive devices conductive and non-conductive;

a first variable drive circuit coupled in series electrical connection with the first control input of the first controllably conductive device to provide a first impedance in series with the first control input; and

a second variable drive circuit coupled in series electrical connection with the second control input of the second controllably conductive device to provide a second impedance in series with the second control input;

wherein the first impedance of the first variable drive circuit is operable to change substantially only in response to a first temperature of the first controllably conductive device and the second impedance of the second variable drive circuit is operable to change substantially only in response to a second temperature of the second controllably conductive device.