LED driver circuit with PWM output

• US 6,586,890 B2
• Filed: 12/05/2001
• Issued: 07/01/2003
• Est. Priority Date: 12/05/2001
• Status: Expired due to Term

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Min, Young-Kee, Hontelé, Bertrand J. E., Clauberg, Bernd
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): A, Minh D
• Application Number:
  US10/012,000
• Publication Number:
  US 20030102819A1
• Time in Patent Office: 573 Days
• Field of Search: 315/224, 315/247, 315/129, 315/209.R, 315/307, 315/308, 363/15, 363/21.11, 363/21.12, 363/21.15, 363/21.17, 362/800
• US Class Current: 315/224
• CPC Class Codes: B60Q 1/2607 comprising at least two indicating lamps
• CPC Class Codes: B60Q 1/2696 Mounting of devices using LEDs
• CPC Class Codes: B60Q 1/44 for indicating braking action or preparation for braking, e.g. by detection of the foot approaching the brake pedal
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

The driver circuit for light emitting diodes (LEDs) of the present invention provides power to LEDs using pulse width modulation (PWM). The driver circuit 100 uses current feedback to adjust power to LED arrays 54 and provides a full light and a dim mode.

Claims

1. A system for supplying power for an LED array, said system comprising:

an oscillator generating an oscillating signal, the oscillating signal having a first state and a second state; and

a power supply operatively coupled to the oscillator, the power supply providing output power and being responsive to the oscillating signal;

wherein said power supply supplies the output power to the LED array when the oscillating signal is in the first state and does not supply the output power to the LED array when the oscillating signal is in the second state.

2. The system of claim 1, wherein the output power is pulse width modulated power.

3. The system of claim 1, wherein the frequency of the power supply is about 20 kHz.

4. The system of claim 1, wherein the frequency of the oscillating signal is much lower than the frequency of the power supply.

5. The system of claim 1, wherein the duty cycle of the oscillating signal is about 10 per cent.

6. The system of claim 1, wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

7. A system for supplying power for an LED array, said system comprising:

means for sensing current to the LED array, said current sensing means generating a sensed current signal;

means for generating a reference signal;

means for comparing the sensed current signal to the reference signal, said comparing means generating a feedback signal;

means for modulating pulse width responsive to the feedback signal, said pulse width modulating means generating a drive signal; and

means for supplying power responsive to the drive signal, said power supplying means supplying current to the LED array.

8. The system of claim 7, further comprising:

means for low frequency oscillating, said low frequency oscillating means generating an oscillating signal having a first state and a second state; and

said power supplying means being responsive to the oscillating signal, said power supplying means supplying current to the LED array during the first state and blocking current to the LED array during the second state.

9. The system of claim 8, wherein the frequency of the oscillating signal is much lower than the frequency of the drive signal.

10. The system of claim 8, wherein the duty cycle of the oscillating signal is about 10 per cent.

11. The system of claim 8, wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

12. The system of claim 8,

wherein said pulse width modulating means is responsive to the oscillating signal from the low frequency oscillating means;

and

wherein said pulse width modulating means supplies the drive signal to said power supplying means during the first state and blocks the drive signal to said power supplying means during the second state.

13. The system of claim 12, wherein said pulse width modulating means synchronizes the drive signal from said pulse width modulating means with the oscillating signal from said low frequency oscillating means.

14. The system of claim 7, further comprising:

means for indicating the LED array is inoperable.

15. A method of supplying power to an LED array, said method comprising:

sensing current to the LED array and generating a sensed current signal;

generating a reference signal;

comparing the sensed current signal to the reference signal;

generating a feedback signal based on the difference between the sensed current signal and the reference signal;

generating a pulse width modulated drive signal based on the feedback signal; and

supplying current to the LED array in response to the pulse width modulated drive signal.

16. The method of claim 15, further comprising:

generating an oscillating signal having a first state and a second state; and

supplying current to the LED array when the oscillating signal is in the first state and blocking current to the LED array when the oscillating signal is in the second state.

17. The method of claim 16, wherein the frequency of the oscillating signal is much lower than the frequency of the pulse width modulated drive signal.

18. The method of claim 16, wherein the duty cycle of the oscillating signal is about 10 per cent.

19. The method of claim 16, wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

20. The method of claim 16, wherein a generation of a pulse width modulated power signal based on the feedback signal includes:

generating a pulse width modulated power signal when the oscillating signal is in the first state; and

blocking the pulse width modulated power signal when the oscillating signal is in the second state.

21. The method of claim 20, further comprising:

synchronizing the pulse width modulated drive signal with the oscillating signal.

22. The method of claim 15, further comprising:

monitoring the LED array; and

indicating when the LED array is inoperable.

23. A circuit for supplying power to an LED array comprising:

a power supply 52, the power supply 52 supplying current to the LED array 54 and being responsive to a drive signal;

a current sensor 60 for sensing current to the LED array 54, the current sensor 60 generating a sensed current signal;

a reference current source 62 for generating a reference signal;

a comparator 58 for comparing the sensed current signal to the reference signal, the comparator 58 generating a feedback signal; and

a PWM control IC 56 responsive to the feedback signal, the PWM control IC 56 generating the drive signal.

24. The circuit of claim 23, further comprising:

a low frequency oscillator, the low frequency oscillator generating an oscillating signal having a first state and a second state; and

wherein said power supply is responsive to the oscillating signal, said power supply supplying current to the LED array during the first state and blocking current to the LED array during the second state.

25. The circuit of claim 24, wherein the frequency of the oscillating signal is much lower than the frequency of the drive signal.

26. The circuit of claim 24, wherein the duty cycle of the oscillating signal is about 10 per cent.

27. The circuit of claim 24, wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

28. The circuit of claim 24,

wherein said PWM control IC is responsive to the oscillating signal from the low frequency oscillator;

and

wherein said PWM control IC supplies the drive signal to said power supply during the first state and blocks the power signal to said power supply during the second state.

29. The circuit of claim 28, wherein said PWM control IC synchronizes the power signal from said PWM control IC with the oscillating signal from the low frequency oscillator.

30. The circuit of claim 23, further comprising:

an LED monitor, said LED monitor generating an LED array inoperable signal when said LED array is inoperable.

31. The circuit of claim 23, wherein said power supply is selected from a group consisting of a buck-boost power supply, a boost power supply, a buck power supply, and a flyback converter.