Spectral shift control for dimmable AC LED lighting

• US 8,643,308 B2
• Filed: 06/27/2010
• Issued: 02/04/2014
• Est. Priority Date: 08/14/2009
• Status: Active Grant

• Current Assignee: Signify North America Corporation (Signify N.V.)
• Original Assignee: Once Innovations Inc. (Signify N.V.)
• Inventors: Grajcar, Zdenko
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): PHAM, THAI N
• Application Number:
  US12/824,215
• Publication Number:
  US 20110210678A1
• Time in Patent Office: 1,318 Days
• Field of Search: 315/185.R, 315/194, 315/195, 315/291, 315/294, 315/297, 315/307, 315/312, 315/192
• US Class Current: 315/307
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/31 Phase-control circuits
• CPC Class Codes: H05B 45/325 Pulse-width modulation [PWM]
• CPC Class Codes: H05B 45/35 Balancing circuits
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/40 Details of LED load circuits
• CPC Class Codes: H05B 45/42 Antiparallel configurations

Abstract

Apparatus and associated methods involve operation of an LED light engine in which a relative intensities of selected wavelengths shift as a function of electrical excitation. In an illustrative example, current may be selectively and automatically diverted substantially away from at least one of a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level. The diversion current may be smoothly reduced in transition as the excitation current or voltage rises substantially above the predetermined threshold level. A color temperature of the light output may be substantially changed as a predetermined function of the excitation voltage. For example, some embodiments may substantially increase or decrease a color temperature output by a solid state light engine in response to dimming the AC voltage excitation (e.g., by phase-cutting or amplitude modulation).

Claims

1. An apparatus for a solid state light engine, the apparatus comprising:

a pair of terminals to receive an applied electrical excitation for a load;

a rectifier receiving the applied electrical excitation and supplying a unidirectional current to the load;

a first network in the load, wherein the first network includes a first plurality of light emitting diodes (LEDs) arranged in series connection to form a first current path for the unidirectional current supplied by the rectifier, the first plurality of LEDs having a first color characteristic;

a second network in the load, wherein the second network includes a second plurality of LEDs arranged in series connection to form a second current path for the unidirectional current supplied by the rectifier, the second plurality of LEDs having a second color characteristic that is substantially different from the first color characteristic;

a bypass path in parallel with said second network and in series relationship with said first network;

a controllable impedance element in the bypass path; and

a dynamic impedance control module coupled to the controllable impedance element, said dynamic impedance control module adapted to dynamically operate the controllable impedance element to increase an impedance of the bypass path as a substantially smooth and continuous function of said current amplitude in response to said current amplitude increasing above a threshold current value, and to permit said current to flow through said first network and to divert substantially all of said current away from said second network while a voltage drop across the bypass path is less than a forward threshold voltage associated with the second network, and smoothly and continuously transitioning substantially all of said current from said bypass path to said second network as said current increases in a substantially smooth and continuous manner while the voltage drop across the bypass path exceeds a forward threshold voltage associated with the second network,

wherein a color characteristic of the combined light output of the first and second networks varies between the first color characteristic and the second color characteristic as a function of the applied electrical excitation.

2. The apparatus of claim 1, wherein the controllable impedance element operates to substantially increase a measured color temperature in response to reduction in an applied voltage.

3. The apparatus of claim 2, wherein the reduction in the applied voltage is associated with a periodic voltage signal processed by a phase-cutting module.

4. The apparatus of claim 2, wherein the reduction in the applied voltage is associated with an amplitude modulated periodic voltage signal.

5. The apparatus of claim 2, wherein the color temperature increases by at least about 3% in response to reduction in the applied voltage.

6. The apparatus of claim 2, wherein the color temperature increases by at least about 28% in response to reduction in the applied voltage.

7. The apparatus of claim 1, wherein the controllable impedance element operates to substantially decrease a color temperature in response to reduction in an applied voltage.

8. The apparatus of claim 7, wherein the reduction in the applied voltage is associated with a periodic voltage signal processed by a phase-cutting module.

9. The apparatus of claim 7, wherein the reduction in the applied voltage is associated with an amplitude modulated periodic voltage signal.

10. The apparatus of claim 7, wherein the color temperature decreases by at least about 16% in response to reduction in the applied voltage.

11. The apparatus of claim 1, wherein the first network further comprises at least one string of one or more series-connected LEDs arranged in a parallel connection with the first current path.

12. The apparatus of claim 1, wherein the second network further comprises at least one string of one or more series-connected LEDs arranged in a parallel connection with the second current path.

13. The apparatus of claim 1, wherein the second network is connected in a series arrangement with the first network.

14. The apparatus of claim 1, wherein the second network is connected in a parallel arrangement with the first network.

15. The apparatus of claim 1, wherein the degree of current diversion by the controllable impedance element varies as a function of the applied electrical excitation.

16. The apparatus of claim 1, wherein the applied electrical excitation comprises a substantially sinusoidal voltage.

17. The apparatus of claim 1, wherein the applied electrical excitation comprises an alternating current.