Method and system for dimming light sources

• US 20060170370A1
• Filed: 01/26/2006
• Published: 08/03/2006
• Est. Priority Date: 02/02/2005
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: Patent-Treuhand-Gesellschaft Fur Elektrische Gluhlampen mbH (Ams-Osram AG)
• Inventors: De Anna, Paolo
• Granted Patent: US 7,642,734 B2
• Time in Patent Office: Days
• US Class Current: 315/185.S
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules

Abstract

Dimming a light source such as a LED over a dimming range (0%-100%) involves adjusting at least one of the intensity (I) and the duty-cycle (DR) of a current flowing through the light source. The dimming range includes at least one portion (L%-H%; 0%-H%) where the light source is fed with a current whose intensity (I) is switched with a given duty cycle (DR) between a non-zero on value and zero, the non-zero on value being a fraction of said rated value (Irated), whereby joint CC and PWM dimming is achieved.

Claims

1. A method of dimming over a dimming range (0%-100%) a light source (LED) having a rated current value (Irated), the method including, over at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%), the operations of;

feeding said light source (LED) with a current whose intensity (I) is switched with a given duty cycle (DR) between an on value and an off value, and

adjusting at least one of said on and off values to a fraction of said rated value (Irated).

2. The method of claim 1, characterized in that it includes, over said at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%), the operations of;

feeding said light source (LED) with a current whose intensity (I) is switched with said given duty cycle (DR) between a non-zero on value and a zero off value, and

adjusting said non-zero on value to a fraction of said rated value (Irated).

3. The method of claim 1, characterized in that it includes the step of selectively varying over said at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%) at least one of;

said given duty cycle (DR), and

said at least one of said on and off values of said switched current.

4. The method of claim 3, characterized in that it includes, over said at least one portion (L%-H%) of said dimming range (0%-100%), the operations of:

gradually bringing to said rated value (Irated) said non-zero on value of said switched current, and

jointly decreasing said given duty-cycle (DR) by gradually increasing the resulting average current through said light source (LED).

5. The method of claim 1, characterized in that said dimming range (0%-100%) includes, in addition to said at least one portion (L%-H%;

0%-H%), at least one of;

a first portion (0%-L%), wherein said light source is fed with a continuous, unswitched current whose intensity (I) is a fraction of said rated value (Irated); and

a further portion (H%-100%), wherein said light source is fed with a current whose intensity (I) is switched with a given duty cycle (DR) between said rated value (Irated) and zero.

6. The method of claim 5, characterized in that it includes the step of selectively varying over said first portion (O%-L%) said intensity (I) being a fraction of said rated value (Irated) of said continuous, unswitched current.

7. The method of claim 5, characterized in that it includes the step of selectively varying said given duty cycle (DR) over said further portion (H%-100%).

8. The method of claim 1, characterized in that it includes the step of adjusting at least one of the intensity (I) and the duty-cycle (DR) of said current flowing through said light source with a given dimming function.

9. The method of claim 8, characterized in that it includes the step of selecting said given dimming function out of a linear and an exponential function.

10. The method of claim 1, characterized in that said light source is a light emitting diode (LED).

11. A circuit for dimming over a dimming range (0%-100%) a light source (LED) having a rated current value (Irated), the circuit including:

a processing circuit (16) for selectively defining (20) at least one dimming level of said light source (LED),

a current source (10) for feeding a current to said light source (LED), said current source (10) being operatively connected to said processing circuit (16) and adjustable in respect of the current fed to said light source (LED) responsive to said dimming level selectively defined by said control unit (20) over at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%) for;

feeding said light source (LED) with a current whose intensity (I) is switched with a given duty cycle (DR) between an on value and an off value, and

adjusting at least one of said on and off values to a fraction of said rated value (Irated).

12. The circuit of claim 11, characterized in that said current source (10) is adjustable in respect of the current fed to said light source (LED) responsive to said dimming level selectively defined by said control unit (20) over said at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%) for;

feeding said light source (LED) with a current whose intensity (I) is switched with said given duty cycle (DR) between a non-zero on value and a zero off value, and

adjusting said non-zero on value to a fraction of said rated value (Irated).

13. The circuit of claim 11, characterized in that said current source (10) is adjustable in respect of the current fed to said light source (LED) for selectively varying over said at least one portion (L%-H%;

0%-H%) of said dimming range (0%-100%) at least one of;

said given duty cycle (DR), and

said at least one of said on and off values of said switched current.

14. The circuit of claim 13, characterized in that said current source (10) is adjustable in respect of the current fed to said light source (LED) over said at least one portion (L%-H%) of said dimming range (0%-100%) for:

gradually bringing to said rated value (Irated) said non-zero on value of said switched current, and

jointly decreasing said given duty-cycle (DR) by gradually increasing the resulting average current through said light source (LED).

15. The circuit of claim 11, characterized in that in that said current source (10) is adjustable in respect of the current fed to said light source (LED) over a dimming range (0%-100%) including, in addition to said at least one portion (L%-H%;

0%-H%), at least one of;

a first portion (0%-L%), wherein said current source (10) feeds said light source (LED) with a continuous, unswitched current whose intensity (I) is a fraction of said rated value (Irated); and

a further portion (H%-100%), wherein said current source (10) feeds said light source (LED) with a current whose intensity (I) is switched with a given duty cycle (DR) between said rated value (Irated) and zero.

16. The circuit of claim 15, characterized in that said current source (10) is configured for selectively varying over said first portion (0%-L%) said intensity (I) being a fraction of said rated value (Irated) of said continuous, unswitched current.

17. The circuit of claim 15, characterized in that said current source (10) is configured for selectively varying said given duty cycle (DR) over said further portion (H%-100%).

18. The circuit of claim 11, characterized in that said processing circuit (16) is configured for controlling said current source (10) for adjusting at least one of the intensity (I) and the duty-cycle (DR) of said current flowing through said light source with a given dimming function.

19. The circuit of claim 18, characterized in that said given dimming function is selected out of a linear and an exponential function.

20. The circuit of claim 11, characterized in that said processing unit (16) includes a microcontroller.