Circuit for interfacing between a conventional traffic signal conflict monitor and light emitting diodes replacing a conventional incandescent bulb in the signal
First Claim
1. A circuit interfacing between a traffic signal'"'"'s load switch and conflict monitor and a plurality of light emitting diodes (LEDs) replacing at least one incandescent signal lamp of said traffic signal, said interface circuit being connected to an input voltage and an input current from said load switch, said interface circuit comprising:
- a regulated current source for driving said LEDs with a regulated load current so as to control said LEDs'"'"' light intensity, said current source providing a power factor of substantially unity by switching said input current so that said input current has an envelope that is substantially the same as said input voltage, said current source being regulated by a feedback signal derived from said load current flowing through said LEDs'"'"'; and
a sensing circuit for simulating an open filament condition to said conflict monitor when said input voltage is at a predetermined voltage level and said load current drops by at least a predetermined amount.
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Accused Products
Abstract
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.
388 Citations
40 Claims
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1. A circuit interfacing between a traffic signal'"'"'s load switch and conflict monitor and a plurality of light emitting diodes (LEDs) replacing at least one incandescent signal lamp of said traffic signal, said interface circuit being connected to an input voltage and an input current from said load switch, said interface circuit comprising:
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a regulated current source for driving said LEDs with a regulated load current so as to control said LEDs'"'"' light intensity, said current source providing a power factor of substantially unity by switching said input current so that said input current has an envelope that is substantially the same as said input voltage, said current source being regulated by a feedback signal derived from said load current flowing through said LEDs'"'"'; and a sensing circuit for simulating an open filament condition to said conflict monitor when said input voltage is at a predetermined voltage level and said load current drops by at least a predetermined amount. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A traffic signal comprising:
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at least one load switch circuit for providing an input voltage and an input current to at least one incandescent signal lamp; at least one conflict monitor designed for verifying that said at least one incandescent signal lamp and at least one other incandescent signal lamp are not on at the same time; a plurality of light emitting diodes (LEDs) replacing said at least one incandescent signal lamp of said traffic signal; and a circuit for interfacing between said at least one load switch circuit, said at least one conflict monitor and said plurality of light emitting diodes, said interface circuit receiving said input voltage and said input current, said interface circuit comprising; a regulated current source for driving said LEDs with a regulated load current so as to control said LEDs'"'"' light intensity, said current source providing a power factor near unity by switching said input current so that said input current has an envelope that is substantially the same as said input voltage, said current source being regulated by a feedback signal derived from said load current flowing through said LEDs'"'"'; and a circuit for simulating an open filament condition to said conflict monitor when said input voltage is at a predetermined voltage level and said load current drops by at least a predetermined amount. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A circuit interfacing between a traffic signal'"'"'s load switch and conflict monitor and a plurality of light emitting diodes (LEDs) replacing at least one incandescent signal lamp of said traffic signal, said interface circuit comprising:
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means for driving said LEDs with a power factor corrected current, said LED driving means providing said power factor corrected current by switching an input current so that said input current has an envelope that is substantially the same as an input voltage, said power factor corrected current being regulated by a feedback signal derived from said power factor corrected current flowing through said LEDs so as to control said LEDs'"'"' light intensity; and means for simulating an open filament condition to said conflict monitor when said input voltage is at a predetermined voltage level and said regulated power factor corrected current drops by at least a predetermined amount. - View Dependent Claims (28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification