Maintaining LED luminous intensity

Details Maintaining LED luminous intensity Maintaining LED luminous intensity

1997-01-10

1998-07-21

Lee, Benny T.

Electric lamp and discharge devices: systems

With radiant energy sensitive control means

Electric switch controlled by the radiant energy responsive...

315158, 3151693, 315224, 315307, 363 89, H05B 3702

Patent

active

057839093

ABSTRACT:
A circuit for maintaining the luminous intensity of a light emitting diode (LED) (12) comprising at least one light emitting diode (LED) (12) for producing an luminous intensity; a sensor (22,24) for sensing a condition proportional to the luminous intensity of the LED (12) and for producing a luminous intensity signal; a power supply (16) electrically connected to the LED (12) for supplying pulses of electrical energy to the LED (12); and wherein the power supply (16) includes a switching device responsive to the luminous intensity signal for adjusting the electrical energy supplied by the pulses per unit of time to adjust the average of the current passing through the LED (12) to maintain the luminous intensity of the LED (12) at a predetermined level. In one instance, the sensor (22) includes means for sensing changes in the operating temperature of the LED (12). In a second instance, the sensor (24) includes means (28) for sensing changes in luminous output of the LED (12). The electrical energy supplied by the pulses per unit of time are adjusted by anyone of (1) varying the frequency, (2) varying the width of the pulses, (3) a combination of frequency and width, or (4) adjusting the phase of the pulses within an a.c. sinusoidal wave form.

REFERENCES:
patent: 1662348 (1928-03-01), Stricker
patent: 2503574 (1950-04-01), Allen
patent: 3919546 (1975-11-01), Lutus
patent: 4587459 (1986-05-01), Blake
patent: 5661645 (1997-08-01), Hochstein
Hewlett Packard Application Brief I-012 Temperature Compensation Circuit for Constant LED Intensity, May 1995.

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