Method and system for dimming light sources

• US 7,642,734 B2
• Filed: 01/26/2006
• Issued: 01/05/2010
• Est. Priority Date: 02/02/2005
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: OSRAM GmbH (Ams-Osram AG)
• Inventors: De Anna, Paolo
• Primary Examiner(s): Owens; Douglas W
• Assistant Examiner(s): A; Minh D
• Application Number:
  US11/339,492
• Publication Number:
  US 20060170370A1
• Time in Patent Office: 1,440 Days
• Field of Search: 315/224, 315/219, 315/307, 315/225, 315/291, 315313-314, 315/315, 315/DIG.4, 315/DIG.2, 315/312, 315/308, 362/800, 345/82
• US Class Current: 315/308
• 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 the rated value (Irated), whereby joint CC and PWM dimming is achieved.

Claims

1. A method for powering a light source at selectable brightness levels over a dimming range, the method comprising the steps of:

partitioning the dimming range (0%-100%) into a plurality of portions; and

feeding a current to the light source in dependence upon both;

(a) a selected brightness level; and

(b) the portion of the dimming range corresponding to the selected brightness level, wherein, for a selected brightness level that is within at least one of the plurality of portions of the dimming range;

(i) the current fed to the light source is a discontinuous, switched current that is switched at a duty cycle between an on value and an off value; and

(ii) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level.

2. The method of claim 1, wherein the off value is substantially equal to zero.

3. The method of claim 1, wherein the light source includes at least one light emitting diode.

4. The method of claim 1, wherein:

the step of partitioning includes partitioning the dimming range (0%-100%) into a first portion (0%-L %), a second portion (L %-H %), and a third portion (H %-100%); and

the step of feeding includes;

(i) for a selected brightness level that is within the first portion (0%-L %) of the dimming range, feeding to the light source a continuous, unswitched current having an intensity that is a fraction of a rated current for the light source, wherein the fraction of the rated current is adjusted in dependence upon the selected brightness level;

(ii) for a selected brightness level that is within the second portion (L %-H %) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between an on value and an off value, wherein;

(a) the duty cycle is adjusted in dependence upon the selected brightness level; and

(b) the on value is a fraction of the rated current, and is adjusted in dependence upon the selected brightness level; and

(iii) for a selected brightness level that is within the third portion (H %-100%) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.

5. The method of claim 4, wherein the off value is substantially equal to zero.

6. The method of claim 4, wherein the light source includes at least one light emitting diode.

7. The method of claim 1, wherein:

the step of partitioning includes partitioning the dimming range into a first portion (0%-H %) and a second portion (H %-100%); and

the step of feeding includes;

(i) for a selected brightness level that is within the first portion (0%-H %) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a fixed duty cycle between an on value and an off value, wherein;

(a) the fixed duty cycle is independent of the selected brightness level; and

(b) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level; and

(ii) for a selected brightness level that is within the second portion (H %-100%) of the dimming range, feeding to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.

8. The method of claim 7, wherein the off value is substantially equal to zero.

9. The method of claim 7, wherein the light source includes at least one light emitting diode.

10. A circuit for powering a light source at selectable brightness levels over a dimming range that is partitioned into a plurality of portions, the circuit comprising:

a processing circuit for defining a selected brightness level for the light source; and

a current generator coupled between the processing circuit and the light source, wherein the current generator is operable to feed a current to the light source in dependence upon both;

(a) the selected brightness level; and

(b) the portion of the dimming range corresponding to the selected brightness level, wherein, for a selected brightness level that is within at least one of the plurality of portions of the dimming range;

(i) the current fed to the light source is a discontinuous, switched current that is switched at a duty cycle between an on value and an off value; and

(ii) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level.

11. The circuit of claim 10, wherein the off value is substantially equal to zero.

12. The circuit of claim 10, wherein the light source comprises at least one light emitting diode.

13. The circuit of claim 10, wherein:

the dimming range (0%-100%) is partitioned into a first portion (0%- L %), a second portion (L % - H %), and a third portion (H %-100%); and

the current generator is further operable;

(i) for a selected brightness level that is within the first portion (0%-L %) of the dimming range, to feed to the light source a continuous, unswitched current having an intensity that is a fraction of a rated current for the light source, wherein the fraction of the rated current is adjusted in dependence upon the selected brightness level;

(ii) for a selected brightness level that is within the second portion (L %-H %) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between an on value and an off value, wherein;

(a) the duty cycle is adjusted in dependence upon the selected brightness level; and

(b) the on value is a fraction of the rated current, and is adjusted in dependence upon the selected brightness level; and

(iii) for a selected brightness level that is within the third portion (H %-100%) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.

14. The method of claim 13, wherein the off value is substantially equal to zero.

15. The method of claim 13, wherein the light source includes at least one light emitting diode.

16. The circuit of claim 10, wherein:

the dimming range is partitioned into a first portion (0%-H %) and a second portion (H %-100%); and

the current generator is further operable;

(i) for a selected brightness level that is within the first portion (0%-H %) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a fixed duty cycle between an on value and an off value, wherein;

(a) the fixed duty cycle is independent of the selected brightness level; and

(b) the on value is a fraction of a rated current for the light source, and is adjusted in dependence upon the selected brightness level; and

(ii) for a selected brightness level that is within the second portion (H %-100%) of the dimming range, to feed to the light source a discontinuous, switched current that is switched at a duty cycle between the rated current and the off value, wherein the duty cycle is adjusted in dependence upon the selected brightness level.

17. The method of claim 16, wherein the off value is substantially equal to zero.

18. The method of claim 16, wherein the light source includes at least one light emitting diode.