LED driver circuit with PWM output

• US 20030102819A1
• Filed: 12/05/2001
• Published: 06/05/2003
• Est. Priority Date: 12/05/2001
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hontele, Bertrand J. E., Clauberg, Bernd, Min, Young-Kee
• Granted Patent: US 6,586,890 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• 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 comprising:

an oscillator 64 generating an oscillating signal, the oscillating signal having a first state and a second state; and

a power supply 52 operatively coupled to the oscillator 64, the power supply 52 providing output power and being responsive to the oscillating signal;

wherein the power supply 52 supplies the output power to the LED array 54 when the oscillating signal is in the first state and does not supply the output power to the LED array 54 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 52 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 52.

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

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

8. The system of claim 1 further comprising means for low frequency oscillating 64, the low frequency oscillating means 64 generating an oscillating signal having a first state and a second state;

and

the power supplying means 52 being responsive to the oscillating signal, the power supplying means 52 supplying current to the LED array 54 during the first state and blocking current to the LED array 54 during the second state.

9. The system of claim 2 wherein the frequency of the oscillating signal is much lower than the frequency of the drive signal.

10. The system of claim 2 wherein the duty cycle of the oscillating signal is about 10 percent

11. The system of claim 2 wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

12. The system of claim 2 wherein the pulse width modulating means 56 is responsive to the oscillating signal from the low frequency oscillating means 64;

and

the pulse width modulating means 56 supplies the drive signal to the power supplying means 52 during the first state and blocks the drive signal to the power supplying means 52 during the second state.

13. The system of claim 6 wherein the pulse width modulating means 56 synchronizes the drive signal from the pulse width modulating means 56 with the oscillating signal from the low frequency oscillating means 64.

14. The system of claim 1 further comprising means for indicating the LED array 54 is inoperable 68.

16. The method of claim 9 further comprising the steps of generating an oscillating signal having a first state and a second state 64;

and

supplying current to the LED array 54 when the oscillating signal is in the first state and blocking current to the LED array 54 when the oscillating signal is in the second state.

17. The method of claim 10 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 10 wherein the duty cycle of the oscillating signal is about 10 percent.

19. The method of claim 10 wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

20. The method of claim 10 wherein the step of generating a pulse width modulated power signal based on the feedback signal further comprises the steps of:

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 14 further comprising the step of synchronizing the pulse width modulated drive signal with the oscillating signal.

22. The method of claim 9 further comprising the steps of:

monitoring the LED array 54; and

indicating when the LED array 54 is inoperable.

24. The circuit of claim 17 further comprising a low frequency oscillator 64, the low frequency oscillator 64 generating an oscillating signal having a first state and a second state;

and

the power supply 52 being responsive to the oscillating signal, the power supply 52 supplying current to the LED array 54 during the first state and blocking current to the LED array 54 during the second state.

25. The circuit of claim 18 wherein the frequency of the oscillating signal is much lower than the frequency of the drive signal.

26. The circuit of claim 18 wherein the duty cycle of the oscillating signal is about 10 percent.

27. The circuit of claim 18 wherein the frequency of the oscillating signal is about 200 to 300 Hertz.

28. The circuit of claim 18 wherein the PWM control IC 56 is responsive to the oscillating signal from the low frequency oscillator 64;

and

the PWM control IC 56 supplies the drive signal to the power supply 52 during the first state and blocks the power signal to the power supply 52 during the second state.

29. The circuit of claim 22 wherein the PWM control IC 56 synchronizes the power signal from the PWM control IC 56 with the oscillating signal from the low frequency oscillator 64.

30. The circuit of claim 17 further comprising an LED monitor, the LED monitor generating an LED array inoperable signal when the LED array 54 is inoperable.

31. The circuit of claim 17 wherein the power supply 52 is selected from the group consisting of a buck-boost power supply, a boost power supply, a buck power supply, and a flyback converter.

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

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

means for generating a reference signal 62;

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

means for modulating pulse width 56 responsive to the feedback signal, the pulse width modulating means 56 generating a drive signal; and

means for supplying power 52 responsive to the drive signal, the power supplying means 52 supplying current to the LED array 54.

15. A method of supplying power to an LED array comprising the steps of:

sensing current to the LED array 60 and generating a sensed current signal;

generating a reference signal 62;

comparing the sensed current signal to the reference signal 58;

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 56; and

supplying current to the LED array 54 in response to the pulse width modulated drive signal 52.

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.