LED driver circuit and method

• US 6,836,081 B2
• Filed: 10/31/2001
• Issued: 12/28/2004
• Est. Priority Date: 12/23/1999
• Status: Expired due to Term

• Current Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.), STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.), STMicroelectronics Incorporated (STMicroelectronics NV), STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Swanson, David F., Lam, Michael K., Criscione, Marcello, Stewart, James W.
• Primary Examiner(s): TRAN, THUY V
• Application Number:
  US09/999,157
• Publication Number:
  US 20030025465A1
• Time in Patent Office: 1,154 Days
• Field of Search: 315/307, 315/308, 315/224, 315/129, 315/247, 315/209.R, 315/309, 363/89, 362/800, 362/543-545
• US Class Current: 315/307
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs

Abstract

An LED driver circuit and method are disclosed where a plurality of arrays of light emitting diodes each have a transistor connected to each respective array of light emitting diodes. A PWM controller has an input for receiving a voltage reference and an output connected to selected transistors for driving the selected transistors and setting a PWM duty cycle for the selected arrays of light emitting diodes to determine the brightness of selected light emitting diodes. An oscillator is connected to the PWM controller for driving the PWM controller.

Claims

1. An LED driver circuit comprising:

a plurality of arrays formed from light emitting diodes;

a transistor connected to each array of the plurality of arrays formed from light emitting diodes;

a PWM controller having an input for receiving a voltage reference and an output connected to selected transistors and arrays of light emitting diodes for driving the selected transistors and setting a PWM duty cycle for the selected arrays of the light emitting diodes for determining brightness of the light emitting diodes;

a feedback loop circuit connected to said light emitting diodes and having a switching controller operatively connected to a source of voltage and a reference voltage for sensing and regulating a load voltage; and

an oscillator connected to the PWM controller and the switching controller for driving the PWM controller.

2. An LED driver according to claim 1, further comprising at least one thermal compensation diode connected within said feedback loop circuit to provide a ramp down of voltage to the selected arrays of light emitting diodes when a predetermined temperature is reached.

3. An LED driver according to claim 2, further comprising a feedback transistor connected within said feedback loop circuit and a comparator operatively connected to said switching controller and said feedback transistor for comparing drive and feedback currents.

4. An LED driver according to claim 1, further comprising a lamp outage detection circuit connected to said PWM controller and said transistors for detecting when a selected number of light emitting diodes are inoperative.

5. An LED driver according to claim 4, wherein said lamp outage detection circuit further comprises a sensing resistor connected to each respective array of light emitting diodes.

6. An LED driver according to claim 1, further comprising an input buffer circuit connected to said PWM controller for receiving voltage signal inputs indicative of a combination of light emitting diodes being lit based on selected operations.

7. An LED driver according to claim 6, wherein said voltage signal inputs comprise tail, stop and turn signal inputs.

8. An LED driver according to claim 1, further comprising a resistor divider circuit for providing a reference voltage to the PWM controller.

9. An LED driver according to claim 1, wherein said transistors connected to the arrays of light emitting diodes, the PWM controller and the oscillator are monolithically formed as one integrated circuit chip.

10. An LED driver according to claim 1, wherein said transistors connected to said arrays of light emitting diodes comprise field effect transistors.

11. An LED driver circuit comprising:

a plurality of arrays of light emitting diodes;

a field effect transistor connected to each array of the plurality of arrays of light emitting diodes;

a PWM controller having an input for receiving a voltage reference and an output connected to selected transistors and arrays of light emitting diodes for driving the selected transistors and setting a PWM duty cycle for the selected arrays of light emitting diodes for determining brightness of the light emitting diodes;

a feedback loop circuit having a switching controller operatively connected to a source of voltage and reference voltage for sensing and regulating a load voltage;

an oscillator connected to the PWM controller and the switching controller for driving the PWM controller; and

a lamp outage detection circuit operatively connected to said PWM controller and said field effect transistors for synchronizing an “

on”

command with a measured current for detecting when a selected number of light emitting diodes are inoperative and compensating for any selected PWM duty cycle.

12. An LED driver according to claim 11, and further comprising at least one thermal compensation diode connected within said feedback loop circuit to provide a ramp down of voltage to the selected arrays of light emitting diodes when a predetermined temperature is reached.

13. An LED driver according to claim 11, further comprising a transistor connected within said feedback loop circuit and a comparator operatively connected to said switching controller and said transistor.

14. An LED driver according to claim 11, wherein said lamp outage detection circuit further comprises a sensing resistor connected to each array of respective light emitting diodes.

15. An LED driver according to claim 11, further comprising an input buffer circuit connected to said PWM controller for receiving voltage signal inputs indicative of a combination of light emitting diodes that being lit based on selected operations.

16. An LED driver according to claim 15, wherein said voltage signal inputs comprise tail, stop and turn signal inputs.

17. An LED driver according to claim 11, further comprising a resistor divider circuit for providing a reference voltage to the PWM controller.

18. An LED driver according to claim 11, wherein said transistors connected to the arrays of light emitting diodes, the PWM controller and the oscillator are monolithically formed as one integrated circuit chip.

19. An LED driver according to claim 11, wherein said transistors connected to said arrays of light emitting diodes comprise field effect transistors.

20. A method of driving an array of light emitting diodes comprising the steps of receiving a voltage reference within a PWM controller and outputting a signal for driving selected transistors connected to respective arrays of light emitting diodes and setting a PWM duty cycle for selected arrays of light emitting diodes to determine brightness of the light emitting diodes, and further comprising a step of receiving voltage signals within an input buffer circuit indicative of what combination of arrays of light emitting diodes should be lit.

21. A method according to claim 20, further comprising a step of detecting when a select number of light emitting diodes are inoperative by sensing resistors connected to each respective light emitting diode.

22. A method of driving an array of light emitting diodes comprising the steps of receiving a voltage reference within a PWM controller and outputting a signal for driving selected transistors that are connected to respective arrays of light emitting diodes and setting a PWM duty cycle for selected arrays of light emitting diodes to determine brightness of the light emitting diodes, and sensing a regulating load voltage by a switching controller located within a feedback loop circuit of the selected arrays of light emitting diodes.

23. A method according to claim 22 further comprising a step of ramping down voltage to the selected arrays of light emitting diodes when a predetermined temperature is reached.

24. A method according to claim 22 further comprising a step of detecting when a select number of light emitting diodes in an array are inoperative by sensing resistors connected to each respective array of light emitting diodes.

25. A method according to claim 22 further comprising a step of receiving voltage signals within an input buffer circuit indicative of what combination of arrays of light emitting diodes being lit.

26. An LED driver circuit comprising:

a plurality of arrays formed from light emitting diodes;

a transistor connected to each array of the plurality of arrays formed from light emitting diodes;

a controller having an input for receiving a voltage reference and an output connected to selected transistors and arrays of light emitting diodes for driving the selected transistors and setting a duty cycle for the selected arrays of light emitting diodes for determining brightness of the light emitting diodes; and

a circuit connected to said light emitting diodes and to a source of voltage and a reference voltage for sensing and regulating a load voltage and providing a ramp down voltage to the selected arrays of light emitting diodes when a predetermined temperature is reached.

27. An LED driver according to claim 26, wherein said controller comprises a PWM controller, and including an oscillator connected to said PWM controller for driving said PWM controller.

28. An LED driver according to claim 26, wherein said circuit for sensing and regulating a load voltage comprises a feedback loop circuit.

29. An LED driver according to claim 28, wherein said feedback loop circuit includes a switching controller operatively connected a source of voltage and a reference voltage.

30. An LED driver according to claim 28, and further comprising a thermal compensation diode connected within said feedback loop circuit to provide the ramp down of voltage to the light emitting diodes when a predetermined temperature is reached.

31. An LED driver according to claim 28, further comprising a feedback transistor connected within said feedback loop circuit and a comparator connected to the feedback transistor for comparing drive and feedback currents.

32. An LED driver according to claim 26 further comprising a lamp outage detection circuit connected to said controller and said transistors connected to the arrays of light emitting diodes for detecting when a selected number of light emitting diodes are inoperative.

33. An LED driver according to claim 32, wherein said lamp outage detection circuit further comprises a sensing resistor connected to each respective array of light emitting diodes.

34. An LED driver according to claim 26 further comprising an input buffer circuit connected to said controller for receiving voltage signal inputs indicative of a combination of light emitting diodes being lit based on selected operations.

35. An LED driver according to claim 34, wherein said voltage signal inputs comprise tail, stop and turn signal inputs.

36. An LED driver according to claim 26 further comprising a resistor divider circuit for providing a reference voltage to the controller.

37. An LED driver according to claim 26, wherein said transistors connected to the arrays of light emitting diodes and said controller are monolithically formed as one integrated circuit chip.