Reduction of harmonic distortion for LED loads
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.
1. A solid state light engine adapted to receive an AC input having an input voltage, the solid state light engine comprising:
a plurality of light emitting diodes (LEDs) arranged in a network adapted to receive a load current based on the input voltage;
wherein the solid state engine is substantially and continuously dimmable without use of a DC power source wherein the frequency of the input voltage is at or between 100 Hz and 400 Hz; and said network is arranged so that said current exhibits less than 30% total harmonic distortion in response to the input voltage having a substantially sinusoidal waveform.