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US 9,578,728 B2Granted
Long life, fail safe traffic light
AssigneeDialight Corporation
InventorsKevin A. Hebborn, Glenn J. Zingler
Life of this patent
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Abstract
The present disclosure is directed to a method for detecting a failure in a signal light. In one embodiment, the method includes monitoring operation of one or more light emitting diodes (LEDs) of the signal light coupled to a constant current driver, detecting a short circuit in at least one of the one or more LEDs and signaling a failure in the signal light when the short circuit is detected.
Claims8
A method for detecting a failure in a signal light, comprising:
- monitoring operation of one or more light emitting diodes (LEDs) of the signal light coupled to a constant current driver;
- detecting a short circuit in at least one of the one or more LEDs, wherein the detecting the short circuit comprises:
- setting a voltage threshold for the signal light via a zener diode;
- measuring a voltage across the one or more LEDs of the signal light;
- and
- determining the short circuit has occurred when the voltage falls below the voltage threshold of the zener diode causing the zener diode to stop conducting, which causes a first transistor in communication with the zener diode to turn off;
- and
- signaling the failure in the signal light when the short circuit is detected, wherein the signaling comprises placing the signal light in a high impedance state by blowing a fuse in response to the voltage falling below the voltage threshold, wherein the fuse is blown by a second transistor in communication with the first transistor that turns on in response to the first transistor turning off.
5 more elements
A light signal circuit comprising:
- an alternating current (AC) to direct current (AC-DC) converter for coupling to an AC power supply;
- a control circuit in communication with the AC-DC converter;
- one or more LEDs coupled to the AC-DC converter;
- an under-current and under-voltage sensing circuit coupled to the one or more LEDs, wherein the under-current and under-voltage sensing circuit comprises:
- a zener diode having a voltage threshold that causes the zener diode to stop conducting;
- a first transistor in communication with the zener diode, wherein the first transistor turns off when the zener diode stops conducting in response to a measured voltage falling below the voltage threshold of the zener diode;
- and
- a second transistor in communication with the first transistor that turns on in response to the first transistor turning off;
- and
- a failed state impedance circuit coupled to the under-current and under-voltage sensing circuit and the control circuit, wherein the failed state impedance circuit goes into a high impendence state by blowing a fuse in the failed state impedance circuit when the second transistor turns on.
7 more elements
Dependencies are inferred from the claim text.