LED power supply with temperature compensation
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United States of America Patent
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-
Aug 29, 2000
Grant Date -
N/A
app pub date -
Aug 11, 1999
filing date -
Aug 11, 1999
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A circuit for driving a plurality of light emitting diodes (LEDs) that includes a power supply and a voltage divide circuit utilizing positive and negative temperature coefficient thermistors to boost the drive voltage to the LEDs as the ambient temperature deviates from room temperature, which compensates for increased electrical resistance of the LEDs at low temperatures and decreased LED light output efficiency at high temperatures. The circuit also provides a signal voltage to indicate the drive current through the LEDs, and includes a transistor to shut down the power supply when the signal voltage drops below a predetermined level (i.e. the number of burned out LEDs exceeds a predetermined number). A compensation circuit utilizes a thermistor to boost the signal voltage as the ambient temperature drops to compensate for the characteristic turn-on voltage of the transistor that increases as the temperature of the transistor drops.
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