PWM controller with automatic low battery power reduction circuit and lighting device incorporating the controller

• US 20030201734A1
• Filed: 01/16/2003
• Published: 10/30/2003
• Est. Priority Date: 04/26/2002
• Status: Active Grant

• Current Assignee: Vector Products Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Vector Products Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Krieger, Michael, Shum, Henry, Randolph, Bruce
• Granted Patent: US 6,870,329 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 39/047 with pulse width modulation from a DC power source
• CPC Class Codes: H05B 41/2853 against abnormal power supply conditions
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A controller for controlling a voltage applied to a load from a power source includes a square wave producing circuit for connection in the circuit with the battery and the lamp. The square wave producing circuit produces a variable duty cycle square wave for controlling application of power to the load in accordance with the duty cycle of the square wave. The square wave producing circuit has a control input for varying the duty cycle of the square wave in response to a voltage at the control input. A voltage varying circuit is connected to the power source for producing a selectively variable voltage that is fed to the control input of the square wave producing circuit for selectively adjusting the duty cycle of the square wave. A low voltage detection circuit is connected to the power source and coupled to the control input of the square wave producing circuit for automatically producing a voltage that decreases the duty cycle of the square wave when the battery voltage decreases to or below a predetermined level.

Claims

1. A control circuit for a load, comprising:

a square wave generator producing a square wave output, a duty cycle of the square wave output being controllable by a control input, the square wave output being coupled to a load; and

a low voltage detection circuit for monitoring the voltage level of a power source and providing a control signal to the control input of the square wave oscillator, to thereby decrease the duty cycle of the square wave output when the voltage level of the power source decreases below a predetermined level.

2. The control circuit of claim 1, wherein the square wave generator comprises a comparator circuit having a threshold level set by the control input.

3. The control circuit of claim 2, further comprising:

a triangular wave oscillator producing a triangle wave signal, wherein the triangle wave signal is provided as input to the square wave generator for comparison to the threshold level by the comparator circuit.

4. The control circuit of claim 1, further comprising:

manual control means for varying the control signal input to the control input of the square wave oscillator.

5. The control circuit of claim 4, wherein the manual control means comprises a potentiometer.

6. The control circuit of claim 4, wherein the manual control means comprises:

a plurality of transistors;

a plurality of resistor means, corresponding in number to the plurality of transistors, each having a different value, and each coupled to a different one of the plurality of transistors; and

a selector switch coupled to select one or none of the plurality of transistors to be conductive.

7. The control circuit of claim 6, further comprising:

an integrated circuit coupled to the selector switch, wherein one or none of the plurality of transistors is enabled to conduct by an output of the integrated circuit generated in response to use of the selector switch.

8. The control circuit of claim 7, wherein the integrated circuit comprises a decade counter.

9. The control circuit of claim 7, wherein the integrated circuit includes a reset input coupled to reset the integrated circuit upon any one of power-up, low power source voltage, and use of the selector switch to turn off the load, wherein the reset of the integrated circuit results in power to the load being cut off and the control circuit entering a power conservation mode.

10. The control circuit of claim 4, wherein the manual control means comprises:

a selector switch; and

an integrated circuit coupled to the selector switch to vary the control signal input to the control input of the square wave oscillator among a plurality of discrete levels.

11. The control circuit of claim 10, wherein the manual control means further comprises:

at least two level resistors, each having a first terminal coupled to a corresponding different output of the integrated circuit, each level resistor having a resistance different from each of the other level resistors; and

a common resistor having one terminal coupled to a second terminal of each of the level resistors another terminal coupled to ground;

wherein the point at which the level resistors are coupled to the common resistor is also coupled to the control input of the square wave oscillator, and wherein the integrated circuit controls the level of the control signal input to the control input of the square wave oscillator by selecting an output coupled to one of the level resistors or to none of the level resistors.

12. The control circuit of claim 11, further comprising:

a number of diodes equal in number to the at least two level resistors, wherein each of the level resistors is coupled to the common resistor via one of the diodes.

13. The control circuit of claim 10, wherein the integrated circuit includes a reset input coupled to reset the circuit upon any one of power-up, low power source voltage, and use of the selector switch to turn off the load, wherein the reset mode results in power to the load being cut off and the integrated circuit entering an initial state.

14. The control circuit of claim 1, wherein the low voltage detection circuit comprises a control transistor, wherein the control transistor is gradually turned off as the voltage level of the power source decreases below the predetermined level.

15. The control circuit of claim 1, further comprising a switching means to which the square wave output is provided, to thereby control application of power to the load.

16. The control circuit of claim 15, wherein the switching means comprises a transistor.

17. The control circuit of claim 1, further comprising a transistor coupled to the square wave generator and arranged so as to permit and shut off input to the square wave generator.

18. The control circuit of claim 17, further comprising:

an integrated circuit having an output coupled to the transistor to control the transistor to permit and shut off input to the square wave generator.

19. The control circuit of claim 18, further comprising:

a selector switch coupled to the integrated circuit;

wherein the integrated circuit includes a reset input; and

wherein the reset input is connected so that the integrated circuit resets when at least one of a low power condition, a power-up condition, or a manual turn-off condition occurs.

20. The control circuit of claim 19, wherein, when the integrated circuit resets, the integrated circuit output coupled to the transistor causes the transistor to shut off input to the square wave generator.

21. The control circuit of claim 1, wherein the load comprises a lamp receiving power from the power source.

22. The control circuit of claim 1, wherein the power source comprises a battery.

23. The control circuit of claim 1, wherein the power source comprises a rechargeable battery.

24. The control circuit of claim 1, wherein the square wave generator comprises a timer circuit.

25. A method of controlling a load, comprising the steps of:

producing a controllable variable duty cycle square wave for controlling application of power to the load in accordance with the duty cycle of the square wave; and

detecting when the voltage of a power source decreases to a predetermined level and upon such detection automatically producing a voltage that decreases the duty cycle of the square wave used for controlling application of power to the load.

26. The method of claim 25, further comprising the step of:

manually controlling the duty cycle of the square wave to control the intensity of the load.

27. The method of claim 25, wherein the step of producing the controllable variable duty cycle square wave comprises the steps of:

providing a fixed frequency triangular wave; and

comparing the triangular wave to a threshold voltage, thereby producing the square wave.

28. The method of claim 27, wherein the voltage that decreases the duty cycle of the square wave, produced by the detecting step, determines the threshold voltage.

29. The method of claim 28, further comprising the step of:

manually adjusting the voltage that decreases the duty cycle of the square wave, produced by the detecting step, so as to manually adjust the threshold voltage.

30. A pulse-width modulation (PWM)-based lamp control circuit comprising:

a square wave generator for producing a square wave output, a duty cycle of the square wave output being controllable by a control input, the square wave output being coupled to the lamp; and

a low voltage detection circuit for monitoring the voltage level of a power source and providing a control signal to the control input of the square wave oscillator, to thereby decrease the duty cycle of the square wave output when the voltage level of the power source decreases below a predetermined level.

31. The control circuit of claim 30, wherein the square wave generator comprises a comparator circuit having a threshold level set by the control input.

32. The control circuit of claim 31, further comprising:

a triangular wave oscillator producing a triangle wave signal, wherein the triangle wave signal is provided as input to the square wave generator for comparison to the threshold level by the comparator circuit.

33. The control circuit of claim 30, further comprising:

manual control means for varying the control signal input from the low voltage detection circuit to the control input of the square wave oscillator.

34. The control circuit of claim 33, wherein the manual control means comprises a potentiometer.

35. The control circuit of claim 33, wherein the manual control means comprises:

a plurality of transistors;

a plurality of resistor means, corresponding in number to the plurality of transistors, each having a different value, and each coupled to a different one of the plurality of transistors; and

a selector switch coupled to select one or none of the plurality of transistors to be conductive.

36. The control circuit of claim 35, further comprising:

an integrated circuit coupled to the selector switch, wherein one or none of the plurality of transistors is enabled to conduct by an output of the integrated circuit generated in response to use of the selector switch.

37. The control circuit of claim 36, wherein the integrated circuit comprises a decade counter.

38. The control circuit of claim 36, wherein the integrated circuit includes a reset input coupled to reset the integrated circuit upon any one of power-up, low power source voltage, and use of the selector switch to turn off the load, wherein the reset of the integrated circuit results in power to the load being cut off and the control circuit entering a power conservation mode.

39. The control circuit of claim 33, wherein the manual control means comprises:

a selector switch; and

an integrated circuit coupled to the selector switch to vary the control signal input to the control input of the square wave oscillator among a plurality of discrete levels.

40. The control circuit of claim 39, wherein the manual control means further comprises:

at least two level resistors, each having a first terminal coupled to a corresponding a different output of the integrated circuit, each level resistor having a resistance different from each of the other level resistors; and

a common resistor having one terminal coupled to a second terminal of each of the level resistors another terminal coupled to ground;

wherein the point at which the level resistors are coupled to the common resistor is also coupled to the control input of the square wave oscillator, and wherein the integrated circuit controls the level of the control signal input to the control input of the square wave oscillator by selecting an output coupled to one of the level resistors or to none of the level resistors.

41. The control circuit of claim 40, further comprising:

a number of diodes equal in number to the at least two level resistors, wherein each of the level resistors is coupled to the common resistor via one of the diodes.

42. The control circuit of claim 39, wherein the integrated circuit includes a reset input coupled to reset the integrated circuit upon any one of power-up, low power source voltage, and use of the selector switch to turn off the load, wherein the reset mode results in power to the load being cut off and the integrated circuit entering an initial state.

43. The control circuit of claim 30, wherein the low voltage detection circuit comprises a control transistor, wherein the control transistor is gradually turned off as the voltage level of the power source decreases below the predetermined level.

44. The control circuit of claim 30, further comprising a switching means to which the square wave output is provided, to thereby control application of power to the lamp.

45. The control circuit of claim 44, wherein the switching means comprises a transistor.

46. The control circuit of claim 30, further comprising a transistor coupled to the square wave generator and arranged so as to permit and shut off input to the square wave generator.

47. The control circuit of claim 46, further comprising:

an integrated circuit having an output coupled to the transistor to control the transistor to permit and shut off input to the square wave generator.

48. The control circuit of claim 47, further comprising:

a selector switch coupled to the integrated circuit;

wherein the integrated circuit includes a reset input; and

wherein the reset input is arranged so that the integrated circuit resets when at least one of a low power condition, a power-up condition, or a manual turn-off condition occurs.

49. The control circuit of claim 48, wherein, when the integrated circuit resets, the integrated circuit output coupled to the transistor causes the transistor to shut off input to the square wave generator.

50. The control circuit of claim 30, wherein the power source comprises a battery.

51. The control circuit of claim 30, wherein the power source comprises a rechargeable battery.

52. A DC-powered lamp comprising the control circuit of claim 30 and further comprising:

a cold-cathode fluorescent lamp, controlled independently of the control circuit of claim 30.

53. The control circuit of claim 30, wherein the square wave generator comprises a timer circuit.