Rapidly developing AC direct drive LED light source technology (Photos)

Figure 1 System application scheme for DC drive LED light source

Seoul Semiconductor Co., Ltd., today's Seoul Semiconductor, invented AC LEDs that can be directly driven by AC in 2005, followed by III-N Technology in the US, and 3N technology to develop a gallium nitride substrate based on MOCVD growth technology. Improve lighting and sensor applications, reduce costs and increase productivity. 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, the "Industrial Technology Research Institute" of Taiwan Province of China also 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 illumination. Indicator lights, 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 Comparison of performance between AC LED 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 photo. The AC LED die is illuminated after the AC is connected. Therefore, only two leads need to be introduced into the AC source to work.

Figure 2 AC LED die arrangement photo and schematic

How AC LED light sources work

The working principle of the AC LED light source is shown in Figure 3. The stack of LED micro-arrays is divided into five strings by an interlaced matrix arrangement. The AC LED die is composed of a rectifier bridge. The two ends of the rectifier bridge are connected to the AC source. The other end is connected with a string of LED dies. The positive half of the alternating current flows along the blue path, the three strings of LED illuminate, the negative half cycle flows along the green path, and three strings of LED dies are illuminated, on the four bridge arms. The LED dies are illuminated in turn, and the LED dies on the bridge arms are simultaneously illuminated. The middle string of LED dies are always illuminated due to sharing. In 60 Hz AC, it will be lit at a frequency of 60 times per second. The DC obtained by the rectifier bridge is pulsating DC, and the LED's illumination is also flashing. The LED has the characteristics of power-off afterglow, and the afterglow can be kept for tens of microseconds. Because the human eye is inert to the flow point memory, the result is The eye's interpretation of the working mode of the LED + light source + afterglow is continuous illumination. LEDs work half the time, half of the time is resting, so heat is reduced by 40% to 20%. Therefore, the life of the AC LED is longer than that of the DC LED.

Figure 3 AC LED light source works

Mature products of AC LEDs such as AX3201 and AX3211 for AC110V and AX3221 and AX3231 for 220V. For AC110V power is 3.3W ~ 4W, working current is 40mA; AC220V power is 3.3W-4W, working current is 20mA (Figure 4). The LED die is bonded directly to the copper-aluminum substrate. The pin is shown in Figure 5.

Figure 4 Seoul Semiconductor's AC LED

Figure 5 AC LED pin diagram

Typical application technology for AC LED

The typical application schematic diagram of AC LED is very simple as shown in Figure 6. The positive temperature coefficient thermistor PTC and the current limiting resistors R1, R2 and R3 are connected to the AC LED at both ends, and 110V or 220V AC can be connected. Enter the lighting work.

When the LED is mass-produced, its impedance has a certain dispersion, and AC LED is also the same. In order to facilitate the high-volume application of downstream manufacturers, the LED light source manufacturer will perform the impedance division on the mass-produced products at the factory, when the customer is in use. The current limiting resistor of the corresponding resistance value can be checked according to the VF binning table provided by the LED light source manufacturer. As shown in Table 2, the VF binning and current limiting resistance meter of the AX3221/AX3231 are shown.

Figure 6 Typical application of AC LED

Table 2 VX bin and current limiting resistor table of AX3221/AX3231

AC LED development

The convenience of AC LED in household power does not require the installation of an AC to DC converter for the lamp like DC LED, which not only saves the cost of the converter, but also avoids the LED light source itself is not broken, but The converter is broken first. The AC-DC converter can be said to be an electronic component that deteriorates over time and is broken. Its life span is shorter than that of the LED light source itself. Therefore, many LED lamps are broken at present, and the LED light source is not exhausted, but LED The AC-DC converter used in the luminaire was broken first. Another feature of AC LEDs is that their processes are arranged in a staggered matrix, which is lit up in turn. It will be lit at 60 times per second in 60 Hz AC, which also makes the life of AC LEDs longer. The DC LED is long.

However, AC LED has two shortcomings at this stage. One is that the luminous efficiency is not as high as the DC LED. This is because the development of DC LED is currently the mainstream. The AC LED has just started, and the luminous efficiency of AC LED can catch up, even exceed DC. LED's. The second is that AC LEDs are at risk of electric shock. Therefore, if AC LEDs are to be applied to LED lighting fixtures, the bare metal fins should be avoided, but the tropicals should be indirectly. This is the core concept of the development of new liquid-filled LED solid-state lighting fixtures.

AC LED has just entered the growth stage, and currently it is not ideal in terms of brightness, power, etc., but the application of AC LED is simple, no need for transformer converter and constant current source, and low cost and high efficiency have shown strong vitality. The technology of AC LED is developing rapidly. In a few years, high-brightness, high-power, low-cost products will be available in large numbers.

references:

[1] Analyze the application and development trend of AC LED. Focus report of Tuoba Industrial Research Institute (2008-12-4). http://

[2] Seoul Semiconductor DataSheet-AX32X0[R]

[3] Seoul Semiconductor DataSheet-AX32X1[R]

[4] Seoul Semiconductor DataSheet-Comparison by lighting source[R]

[5] Seoul Semiconductor DataSheet-About Q&A[R]