Analysis of the principle and application technology of AC LED light source

As the fourth-generation lighting fixtures of green, energy-saving, energy-saving and long-life, LED light sources have sprung up, attracted wide attention and are rapidly developing in full swing. The current LED light source is a semiconductor device that operates at a low voltage (VF=2→3.6V) and a large current (IF=200→1500mA), and must provide a suitable DC current to emit light normally. The technology of direct current (DC) driving LED light source has become more and more mature. Since the power supply used in our daily lighting is high voltage AC (AC 100 ~ 220V), it is necessary to use the buck technology to obtain a lower voltage. The transformer or switching power supply is stepped down, and then the alternating current (AC) is converted into direct current (DC) and then converted into a direct current constant current source to cause the LED light source to emit light. Therefore, the system application scheme of DC-driven LED light source must be: transformer + rectification (or switching power supply) + constant current source (Figure 1).

LED lamps must have a certain amount of space to house this module, but for E27 standard screw luminaires, the space is very limited and difficult to place. Whether it is via transformer + rectification or switching power supply step-down, the system will have a certain amount of loss. When the DC LED is switched between AC and DC, about 15% to 30% of the power is lost, and the system efficiency is difficult to achieve more than 90%. . If the LED light source can be directly driven by AC (AC), the system application scheme will be greatly simplified, and the system efficiency will easily reach 90% or more.

Figure 1: System application of DC-driven LED light source

As early as 2005, the Korean company invented AC LEDs that can be directly driven by AC, followed by III-N Technology in the US, and 3N technology developed a gallium nitride substrate based on MOCVD growth technology to enhance lighting and sensor applications. And reduce costs and increase production efficiency. Provides 6-inch production technology for large and small silicon LEDs. 3N invented the single-chip AC light-emitting diode (AC LED), which has established a comprehensive patent portfolio to protect and improve technology, firmly establishing its proprietary position, and is the premier large-scale commercial production of AC LED products.

In 2008, Taiwan Industrial Technology Research Institute completed AC LED products that can be industrially produced and have practical application system solutions. It can be directly plugged into AC 110V AC voltage of 60Hz or higher to make AC light, which is used for indication. Lamps, neon lights, and low wattage lights can effectively solve the shortcomings of existing LEDs that cannot be used directly under AC sources, resulting in higher product application costs. Taiwan Industrial Technology Institute's On Chip AC LED (on-chip AC LED) won the 2008 R&D 100 Award, which is known as the American Industry Innovation Oscar. Nowadays, only the United States, South Korea and Taiwan have this technology in the world. The Taiwan Industrial Technology Research Institute has developed the process technology of white, blue and green AC LED, which is not only synchronized with the international market, but also one of the world leaders.

Advantages of AC LED lamps

Compared with incandescent lamps, halogen lamps, fluorescent fluorescent lamps, fluorescent energy-saving lamps, and DC LED lamps, AC LED lamps have more energy-saving, longer life, and more energy-efficient. AC LED illumination eliminates the need for costly AC/DC converters and constant current sources. The performance comparison between AC LED and existing lighting fixtures is shown in Table 1.

Table 1: Performance comparison between AC LEDs and existing lighting fixtures

AC LED source ultra-fine grain with a special interlaced matrix arrangement

The major technological breakthrough of AC LED light source is the special arrangement and combination technology of ultra-fine LED die in packaging. At the same time, the diode characteristic of LED PN junction is used as rectification, and semiconductor process plays a very important role. AC LEDs are integrated into a stack of tiny grains through a semiconductor process, using a staggered matrix arrangement process, and adding a bridge circuit to the chip design, so that the AC current can be double-conducted to achieve illumination. The arrangement of the crystal grains is shown in Figure 2. The left picture shows the AC LED die in a staggered matrix arrangement. The right small picture shows the actual AC LED die arrangement. The AC LED die is illuminated after the AC is connected. Only two leads need to be introduced into the AC source to work.

Figure 2: AC LED die arrangement photo and schematic