AC powered light emitting diode array circuits for use in traffic signal displays

An LED array circuit powered by a substantially sinusoidal AC voltage source of known frequency, comprising:

• a) a plurality of series connected LEDs having first and second terminal nodes, coupled to and across the substantially sinusoidal AC voltage source, said plurality of series connected LEDs comprising a plurality of LED pairs, each LED pair comprising two oppositely polarized LEDs coupled to each other in parallel, and each LED pair being series connected to another LED pair;
• b) an inductor arranged in series with and coupling one of said first and second terminal nodes to the substantially sinusoidal AC voltage source;
• and
• c) a first capacitor coupled in parallel to said plurality of series connected LEDs at said first and second terminal nodes, wherein said inductor and said first capacitor form an impedance converter circuit which is tuned to the known frequency of the substantially sinusoidal AC voltage source thereby effectively converting the AC voltage source into substantially an AC current source, wherein
• said plurality of series connected LEDs comprising a number of LEDs sufficient to cause a voltage drop across said first set of LEDs to be greater than a peak voltage of the AC voltage source.

An LED array circuit powered by a substantially sinusoidal AC voltage source of known frequency, comprising:

• a) a first set of LEDs arranged as a first plurality of LED pairs, each LED pair comprising two oppositely polarized LEDs coupled to each other in parallel, and each LED pair being series connected to another LED pair, said first set of LEDs having first and second terminal nodes, coupled to and across the substantially sinusoidal AC voltage source;
• b) an inductor arranged in series with and coupling one of said first and second terminal nodes to the substantially sinusoidal AC voltage source;
• and
• c) a first capacitor coupled in parallel to said first set of LEDs at said first and second terminal nodes, wherein said inductor and said first capacitor form an impedance converter circuit which is tuned to the known frequency of the substantially sinusoidal AC voltage source thereby effectively converting the AC voltage source into substantially an AC current source, said inductor having an inductance value chosen to provide a desired current for lighting said first set of LEDs, and said inductor chosen to have a high impedance while providing energy efficiency.