Patent number 8487546 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates in general to the field of electronics and lighting, and, more specifically, to a light emitting diode (LED) system and method with accurate current control.
"Commercially practical incandescent light bulbs have been available for over 100 years. However, other tight sources show promise as commercially viable alternatives to the incandescent light bulb. LEDs are becoming particularly attractive as main stream; light sources in part because of energy savings through high efficiency light output and environmental incentives such as the reduction of mercury.
"LEDs are semiconductor devices and are driven by direct current. The lumen output intensity (i.e. brightness) of the LED approximately varies in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the intensity of the LED and decreasing current supplied to the LED dims the LED, i.e. decreases the brightness of the LED. Current can be modified by either directly reducing the direct current level to the white LEDs or by reducing the average current through duty cycle modulation.
"Dimming a light source saves energy when operating a light source and also allows a user to adjust the intensity of the light source to a desired level. Many facilities, such as homes and buildings, include light source dimming circuits (referred to herein as 'dimmers').
"FIG. 1 depicts an LED lighting system 100 that supplies power to light emitting diodes (LEDs) 102 and dims the LEDs 102 in accordance with a dimming level indicated by the phase modulated signal V.sub..PHI.. The Voltage source 104 supplies an alternating current (AC) input voltage V.sub.IN. Full, diode bridge rectifier 108 rectifies the input voltage V.sub.IN. The mains voltage source 104 is, for example, a public utility, and the input voltage V.sub.DIM is, for example, a 60 Hz/120 V rectified voltage in
"Switching power supply 110 utilizes switching power converter technology to convert the phase modulated signal V.sub..PHI. into an output voltage V.sub.OUT. The output voltage V.sub.OUT is sufficient to bias the LEDs 102. Switching power supply 110 also supplies an LED current i.sub.LED to illuminate the LEDs 102.
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