Digital Lumens, Inc.

Hugh Medal

Frederick Marshall Morgan

Scott D Johnston

John Francis Egan

Christopher L Elledge

Frederick M Morgan

Christopher Elledge

Light-emitting diodes (LEDs) generate light more efficiently than high-intensity discharge lamps or high-intensity fluorescent lamps. Driving a series of LEDs with a constant-voltage primary supply and a low-voltage LED driver keeps efficiency high. Unfortunately, LED forward voltage varies as a function of temperature: at low temperature, the forward voltage rises. Placing the LEDs in series magnifies the forward voltage increases. This makes it difficult to drive a series of LEDs at low temperature with a constant-voltage supply because the forward voltage can exceed the power supply voltage. To account for this behavior, an exemplary LED lighting fixture includes a 'bypass' circuit that, when engaged, effectively removes at least one LED from each series string of LEDs to bring the total forward voltage below the power supply voltage. The low-voltage driver circuit monitors temperature, and engages the 'bypass' circuit when necessary to ensure that DC voltage is not exceeded.

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Everett, MA, United States of America

Hugh Medal