ARCHITECTURE FOR HIGH POWER FACTOR AND LOW HARMONIC DISTORTION LED LIGHTING

• US 20110109244A1
• Filed: 10/28/2010
• Published: 05/12/2011
• Est. Priority Date: 10/28/2009
• Status: Active Grant

• Current Assignee: Signify North America Corporation (Signify N.V.)
• Original Assignee: Once Innovations Inc. (Signify N.V.)
• Inventors: Grajcar, Zdenko
• Granted Patent: US 8,531,136 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• 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 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

Exemplary apparatus and associated methods involve a bypass module for modulating conductivity of one or more current paths to provide a first set of LEDs that are conducting near minimum output illumination and having a larger conduction angle than that of a second set of LEDs that conduct at a maximum output illumination. In an illustrative example, the conductivity of a bypass path in parallel with a portion of the second set of LEDs may be reduced while the AC input excitation is above a predetermined threshold voltage or current. The bypass path may be operated to provide a reduced effective turn-on voltage while the input excitation is below the predetermined threshold. For a given maximum output illumination at a maximum input excitation, the bypass module may control current through selected LEDs to construct an input current waveform with substantially improved power factor and reduced harmonic distortion.

Claims

1. A method of electrically exciting a light engine, the method comprising:

processing a periodic waveform of alternating polarity to form an input excitation signal with a voltage amplitude reduced to substantially zero for a selected phase angle;

providing a network of light emitting diodes (LEDs) comprising a first group of LEDs arranged in series connection with a second group of LEDs;

applying the input excitation signal to the network of LEDs;

diverting current away from the second group of LEDs in response to the input excitation signal voltage less than an effective forward voltage of the network of LEDs;

modulating the selected phase angle within a range of phase angles below a threshold phase angle to produce a corresponding modulation in a luminance of the first group of LEDs; and

,

maintaining a substantially constant luminance of the second group of LEDs while modulating the selected phase angle within the range of phase angles below the threshold phase angle.

2. The method of claim 1, further comprising modulating the selected phase angle in response to an analog control signal.

3. The method of claim 2, wherein processing the periodic waveform of alternating polarity to form an input excitation signal with a voltage amplitude reduced to substantially zero over the selected phase angle further comprises receiving a control signal and, in response to information contained in the control signal, reducing the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to the information in the control signal.

4. The method of claim 3, wherein reducing the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to the information contained in the control signal comprises delaying application of the periodic waveform to the network of LEDs during at least one of the periods of the periodic waveform, wherein a length of the delay is responsive to the information contained in the control signal.

5. The method of claim 3, wherein reducing the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to the information contained in the control signal comprises advancing reduction of the excitation voltage signal to zero during at least one of the periods, wherein a length of the advance is responsive to the information contained in the control signal.

6. The method of claim 2 further comprising, receiving the analog control signal generated by a digital-to-analog converter in response to a command from a processor executing a program of instructions to modulate a luminance output by the light engine.

7. The method of claim 2, wherein the substantially periodic waveform of alternating polarity comprises a substantially sinusoidal voltage waveform.

8. The method of claim 1, wherein processing the periodic waveform of alternating polarity to form the input excitation signal with a voltage amplitude reduced to substantially zero for a selected phase angle further comprises providing a phase-cut modulator configured to reduce a conduction angle of the periodic waveform of alternating polarity in response to a control input signal.

9. The method of claim 7, wherein the control input signal comprises a single analog signal.

10. The method of claim 1, wherein processing the periodic waveform of alternating polarity to form the input excitation signal further comprises rectifying the periodic waveform of alternating polarity to form a waveform having unidirectional polarity.

11. The method of claim 1, wherein the first group of LEDs comprises at least one LED having a substantially different spectral characteristic than any of the LEDs in the second group of LEDs.

12. The method of claim 1, wherein the second group of LEDs comprises at least one LED having a substantially different spectral characteristic than any of the LEDs in the first group of LEDs.

13. The method of claim 1, wherein a current through the second group of LEDs exhibits a characteristic shape of a substantially sinusoidal waveform shape when the input excitation voltage exceeds the effective forward voltage threshold of the network of LEDs.

14. The method of claim 13, further comprising providing one or more resistors in series with the second group of LEDs to control a peak current amplitude through the network of LEDs.

15. The method of claim 1, wherein the selected phase angle within the range of phase angles below the threshold phase angle corresponds to the input excitation signal below the effective forward voltage of the network of LEDs.

16. An illumination system comprising:

a phase control input port to receive an input control signal;

a phase-cut module coupled to the phase control input port and configured to process a periodic waveform of alternating polarity to form an input excitation signal with a voltage amplitude reduced to substantially zero for a phase angle selected in response to the input control signal;

a rectifier for converting the input excitation signal to a unipolar voltage signal;

a network of light emitting diodes (LEDs) coupled to receive the input excitation signal from the rectifier, the network of LEDs comprising a first group of LEDs arranged in series connection with a second group of LEDs;

a bypass module to divert current away from the second group of LEDs in response to the input excitation signal voltage greater than an effective forward voltage of the first group of LEDs and less than an effective forward voltage of the network of LEDs;

wherein a luminance of the first group of LEDs modulates in substantial correspondence with the input control signal modulating the selected phase angle within a range of phase angles below a threshold phase angle, and the second group of LEDs maintains a substantially constant luminance while modulating the selected phase angle within the range of phase angles below the threshold phase angle.

17. The system of claim 16, wherein the network of LEDs are configured as a module with terminals for making connection to the bypass module.

18. The method of claim 16 wherein the phase-cut module reduces the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to information contained in the control signal.

19. The method of claim 18, wherein reducing the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to the information contained in the control signal comprises delaying application of the periodic waveform to the network of LEDs during at least one of the periods of the periodic waveform, wherein a length of the delay is responsive to the information contained in the control signal.

20. The method of claim 18, wherein reducing the voltage amplitude of the input excitation signal to zero only during a portion of the period of the excitation voltage waveform that corresponds to the information contained in the control signal comprises advancing reduction of the excitation voltage signal to zero during at least one of the periods, wherein a length of the advance is responsive to the information contained in the control signal.