Architecture for high power factor and low harmonic distortion LED lighting
First Claim
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 first portion of a periodic cycle of the periodic waveform;
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 being less than an effective forward voltage of the network of LEDs; and
delaying conduction of current through the first or second groups of LEDs for a second portion of the periodic cycle of the periodic waveform longer than the first portion to produce a corresponding decrease in an average luminance of the first group of LEDs while maintaining a substantially constant luminance of the second group of LEDs.
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Accused Products
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.
53 Citations
18 Claims
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1. A method of electrically exciting a light engine, the method comprising:
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processing a periodic waveform of alternating polarity to form an input excitation signal with a voltage amplitude reduced to substantially zero for a first portion of a periodic cycle of the periodic waveform; 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 being less than an effective forward voltage of the network of LEDs; and delaying conduction of current through the first or second groups of LEDs for a second portion of the periodic cycle of the periodic waveform longer than the first portion to produce a corresponding decrease in an average luminance of the first group of LEDs while maintaining a substantially constant luminance of the second group of LEDs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An illumination system comprising:
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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 first portion of a periodic cycle of the periodic waveform 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; and 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 decreases in substantial correspondence with the input control signal while the second group of LEDs maintains a substantially constant luminance when conduction of current through the first or second groups of LEDs is delayed for a second portion of the periodic cycle of the periodic waveform longer than the first portion. - View Dependent Claims (15, 16, 17, 18)
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Specification