METHOD AND APPARATUS FOR CONTROLLING DIMMING LEVELS OF LEDS

• US 20120194079A1
• Filed: 08/18/2010
• Published: 08/02/2012
• Est. Priority Date: 08/26/2009
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Clauberg, Bernd, Greischar, Richard, Shrotriya, Ameya
• Granted Patent: US 8,629,619 B2
• Time in Patent Office: Days
• US Class Current: 315/125
• CPC Class Codes: H05B 31/50 specially adapted for ac
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

Circuits useful in achieving efficient current control of LEDs based on a dimming control input are described. The circuits use a combination of PWM dimming and analog dimming to achieve a highly efficient LED driver over a wide range of dimming from near 0% to 100% light output.

Claims

1. A dimming circuit for an LED, comprising:

a current controller configured to receive a dimming input and to output a pulse width modulation signal (PWM) and a reference voltage;

a current converter configured to provide an output current; and

a shunt switch connected to the controller and to the current converter and between the current controller and the LEDs, wherein the shunt switch is non-conducting when the dimming input exceeds a threshold level.

2. A dimming circuit as claimed in claim 1, wherein the shunt switch is conducting when the dimming input is less than the threshold level.

3. A dimming circuit as claimed in claim 1, further comprising a first inductor connected between the current converter and the shunt switch, wherein a current through the first inductor is proportional to the threshold level when the shunt switch is non-conducting.

4. A dimming circuit as claimed in claim 1, wherein the controller comprises circuitry configured to receive a dimming input and output the PWM signal and the reference voltage.

5. A dimming circuit as claimed in claim 4, wherein the controller comprises a memory comprising a correlation of the dimming input to the PWM signal and the reference voltage.

6. A dimming circuit as claimed in claim 1, wherein the controller comprises a programmable logic device (PLD) configured to receive a dimming input and output the PWM signal and the reference voltage.

7. A dimming circuit as claimed in claim 1, wherein the threshold level is a value representative of a percentage of a maximum drive current to the LEDs.

8. A dimming circuit as claimed in claim 7, wherein the value is in the range of approximately 0% of the maximum current level to approximately 10% of the maximum current level.

9. A dimming circuit for an LED, comprising:

a controller configured to receive a dimming input, and to provide a pulse width modulation signal (PWM) and a reference voltage;

a current converter configured to provide an output current; and

a buck converter connected between the LEDs and current converter, wherein the buck converter comprises a shunt switch that is non-conducting when the dimming input is less than a threshold level.

10. A dimming circuit as claimed in claim 9, wherein the shunt switch is conducting when the dimming input is greater than the threshold level.

11. A dimming circuit as claimed in claim 9, further comprising a first inductor connected between the current converter and the buck converter, wherein a current through the first inductor is proportional to the threshold level when the shunt switch is conducting.

12. A dimming circuit as claimed in claim 9, wherein the controller comprises a microprocessor configured to receive a dimming input and output the PWM signal and the reference voltage.

13. A dimming circuit as claimed in claim 12, wherein the controller comprises a memory comprising a correlation of the dimming input to the PWM signal and the reference voltage.

14. A dimming circuit as claimed in claim 9, wherein the controller comprises a programmable logic device (PLD) configured to receive a dimming input and output the PWM signal and the reference voltage.

15. A dimming circuit as claimed in claim 9, wherein the threshold level comprises a value representative of a percentage of a maximum drive current to the LEDs.

16. A dimming circuit as claimed in claim 9, wherein the value is in the range of approximately 0% of the maximum current level to approximately 10% of the maximum current level.