Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Patent
1999-08-11
2000-08-29
Wong, Don
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
315149, 315225, 340907, H02H 504
Patent
active
061117390
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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Chuang Han-Jen
Wu Chen-ho
Lee Wilson
Leotek Electronics Corporation
Wong Don
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