| 摘要 |
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.
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