Light emitting diodes for high AC voltage operation and general lighting

#The present invention relates to single-chip light emitting diodes (LED), and more particularly to single-chip LEDs which can operate under standard alternating-current (AC) high voltage (110 V, 220 V, etc.) conditions for various applications, including general lighting.

#LEDs are used in displays, as indicator lights, for traffic lights, for communications, and for optical interconnects. With the realization of high brightness blue/green and violet LEDs made from the III-nitride semiconductor family InN, GaN, AIN and their alloys recently it is now possible that LEDs may be used for general lighting applications in residential houses and commercial buildings. LEDs have already found niche applications in the area of lighting, such as passenger side reading lights in vehicles. Because of the potential energy, environment and national security benefits, there is increasing national interest in creating a partnership—of industry, universities and national laboratories—aimed at accelerating the development of Solid-State Lighting science and technology. A nation-wide program called “Next-Generation Lighting Initiative” has been lunched by the Department of Energy (DOE).

#Several methods have been proposed and employed to achieve white light emission from LEDs. The first and the only commercial product is to use blue LEDs made of III-nitrides to generate white light by coating the blue LED chips with yellow phosphors. Phosphors down convert part of the shorter wavelength blue light to a yellow wavelength visible yellow light. Through color mixing, the eye sees white when two colors are properly balanced. Other proposed method includes using UV LEDs (more efficient sources) to pump three-color phosphors (red, blue, green, RBG) or to combine three color (RBG) LEDs to get white emission.

#FIG. 1 is a diagrammatic plan view of a single-chip high voltage AC LED of the present invention.

#FIG. 2 is an equivalent circuit of the single-chip high voltage AC LED of FIG. 1.

#FIG. 3 is a diagrammatic cross sectional illustration showing integration between adjacent LED elements within the single-chip high voltage AC LED.

#Referring to FIG. 1, a single-chip high voltage AC LED 10 is illustrated connected to a high voltage AC power supply 12. As shown, the single-chip high voltage AC LED 10 effectively consists of two arrays of series-connected individual smaller LEDs 14. The two arrays of series-connected individual LEDs are then connected to the opposite polarities of the high voltage AC power source 12. Each LED array could be made into one or many columns to fit the desired geometrical shape of the single-chip high voltage LED. In FIG. 1, each array consists of two columns for illustration.

#Referring to FIGS. 1 and 2, the first array 16 of the single-chip AC LED 10 provides a number of series-connected smaller LEDs 14. The cathode of one LED 14 is connected to the anode of the next LED to form the array 16. The array 16 of LEDs 14 presents a positive terminal corresponding to the cathode of the last LED (shown at the bottom of the first column of array 16 in FIG. 1 and shown at the top of array 16 in FIG. 2), and a negative terminal corresponding to the anode of the first LED (shown at the bottom of the second column of array 16 in FIG. 1 and shown at the bottom of the array 16 in FIG. 2). The second array 18 of the single-chip AC LED 10 provides an equal number of series-connected smaller LEDs 14. The cathode of one LED 14 is connected to the anode of the next LED to form the array 18. The array 18 of LEDs 14 also presents positive and negative terminals, which are connected to the opposite terminal of array 16. When the AC cycle is positive, the LEDs 14 of array 16 are forward biased and thus energized. At the same time, the LEDs 14 of array 18 are reverse biased, and hence turned off. When the AC cycle is negative, the LEDs 14 of array 16 are reverse biased and hence turned off, while the LEDs 14 of array 18 are forward biased and thus turned on.

#The arrays 16 and 18 are connected to different polarities of the AC power source for high voltage AC operation. The arrays 16 and 18 of smaller LEDs 14 are alternatively turned on and off at a rate corresponding to the frequency of the AC source. Common frequencies for public utilities are 60 Hz or 50 Hz, for example. Thus for a 60 Hz AC power source, arrays 16 and 18 are alternatively energized at a 60 Hz rate. In this manner, to the naked eye, the single-chip high voltage AC LED 10 always appears to be on.