06150771 is referenced by 168 patents and cites 133 patents.

A circuit for interfacing between a conventional traffic signal's control monitor and a plurality of light emitting diodes (LEDs) replacing an incandescent lamp of the traffic signal is disclosed. The interface circuit includes a current source for driving the LEDs with a regulated power factor corrected current. Compatibility with traditional conflict monitors is achieved through a circuit that short circuits incoming current to indicate full turn off of the signal and opens up to indicate full turn on of the signal, and through an "OFC" circuit which presents an open circuit to the conflict monitor upon failure of the traffic signal LEDs. Quick turn-off of the traffic signal LEDs is accomplished with a switching circuit that reduces current flowing through the LEDs below the range for visible turn-off. To minimize light reduction in case of LED failure, the traffic signal LEDs are arranged in either multiple strings of LEDs connected in parallel though multiple substring connections between groups of LEDs, or in a single string of LEDs with reverse biased zener diodes connected in parallel with groups of LEDs.

Title
Circuit for interfacing between a conventional traffic signal conflict monitor and light emitting diodes replacing a conventional incandescent bulb in the signal
Application Number
8/873030
Publication Number
6150771
Application Date
June 11, 1997
Publication Date
November 21, 2000
Inventor
Bradford J Perry
Cumby
TX, US
Agent
Nixon & Vanderhye P C
Assignee
Precision Solar Controls
TX, US
IPC
H05B 37/02
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