Reduction of Harmonic Distortion for LED Loads

摘要

Apparatus and associated methods reduce harmonic distortion of a excitation current by diverting the excitation current substantially away from a number of LEDs arranged in a series circuit until the current or its associated periodic excitation voltage reaches a predetermined threshold level, and ceasing the current diversion while the excitation current or voltage is substantially above the predetermined threshold level. In an illustrative embodiment, a rectifier may receive an AC (e.g., sinusoidal) voltage and deliver unidirectional current to a string of series-connected LEDs. An effective turn-on threshold voltage of the diode string may be reduced by diverting current around at least one of the diodes in the string while the AC voltage is below a predetermined level. In various examples, selective current diversion within the LED string may extend the input current conduction angle and thereby substantially reduce harmonic distortion for AC LED lighting systems.

主权项

1. A method of conditioning current in a light engine, the method comprising:
providing a pair of input terminals adapted to receive a periodic excitation voltage; receiving a current of equal magnitude and opposite polarity into each one of the pair of terminals, said current flowing in response to the excitation voltage; providing a plurality of light emitting diodes (LEDs) arranged in a first network, said first network arranged to conduct said current in response to the excitation voltage exceeding at least a forward threshold voltage associated with the first network; providing a plurality of LEDs arranged in a second network in series relationship with said first network; providing a bypass path in parallel with said second network and in series relationship with said first network; dynamically increasing an impedance of the bypass path as a substantially smooth and continuous function of said current amplitude in response to said current amplitude increasing in a range above a threshold current value; substantially smoothly and continuously reducing current flow through the bypass path in response to a substantially smooth and continuous increase in the voltage drop across the bypass path in a range above the forward threshold voltage associated with the second network.