The working principle of AC LED light source

- Feb 15, 2021-

As a fourth-generation lighting fixture with green, energy-saving, power-saving, and long-life LED light sources, LED light sources have sprung up, attracting wide attention, and are developing rapidly. The current LED light source is a low voltage (VF=2→3.6V), high current (IF=200→1500mA) semiconductor device, which must provide a suitable DC current to normally emit light. The technology of direct current (DC) driving the LED light source to emit light has become more and more mature. Since the power supply for our daily lighting is high-voltage alternating current (AC100-220V), we must use step-down technology to obtain a lower voltage. Transformers are commonly used. Or the switching power supply is stepped down, and then the alternating current (AC) is converted into direct current (DC), and then converted into a constant current source to promote the LED light source to emit light. Therefore, the system application scheme of DC driving LED light source must be: transformer + rectifier (or switching power supply) + constant current source.


There must be a certain amount of space in the LED lamp to install this module, but for the E27 standard screw lamp, the space is very limited and difficult to install. Whether it is transformer + rectifier or switching power supply step-down, the system will have a certain amount of loss. When DC LED is converted between AC and DC, about 15-30% of the power is lost, and the system efficiency is difficult to achieve more than 90%. If alternating current (AC) can be used to directly drive the LED light source to emit light, the system application scheme will be greatly simplified, and the system efficiency will easily reach more than 90%.


AC LED light source ultra-fine grains are arranged in a special staggered matrix


The major technological breakthrough of AC LED light source is the special arrangement and combination technology of ultra-fine LED dies during packaging. At the same time, the diode characteristics of the LED PN junction are used as rectification. The semiconductor process plays a very important role in the development of AC LED technology. AC LED is integrated into a pile of tiny dies using semiconductor manufacturing process, using a staggered matrix arrangement process, and adding a bridge circuit to the chip design, so that the AC current can be bidirectionally conducted to achieve light emission. The arrangement of the dies is shown in Figure 1. The left picture is a schematic diagram of the AC LED dies in a staggered matrix arrangement, and the right small picture is a photo of the actual AC LED dies arrangement. The AC LED dies emit light after being connected to AC power. It only needs two leads to lead into AC power source to be able to emit light.



The working principle of AC LED light source

The working principle of AC LED light source is shown in Figure 2. A pile of small LED dies are divided into five strings using a staggered matrix arrangement process. The string of AC LED dies is similar to a rectifier bridge, and the two ends of the rectifier bridge are connected to AC power supply. , The other two ends are connected to a string of LED dies, the positive half of the alternating current flows along the blue path, 3 strings of LED dies emit light, the negative half of the cycle flows along the green path, and there are 3 strings of LED dies that emit light. The LED dies emit light in turns, and the LED dies on the opposite bridge arms emit light at the same time, and the middle string of LED dies keep emitting light due to sharing. It turns on at a frequency of 60 times per second in a 60Hz alternating current. The DC obtained by the rectifier bridge is pulsating DC, and the light of the LED is also flashing. The LED has the characteristics of continuous afterglow after power off. The afterglow can be maintained for tens of microseconds. Because the human eye is inert to the memory of the flowing light point, people The eye's interpretation of the LED light source's luminous + afterglow working mode is continuous luminescence. LED is working half of the time and resting half of the time, so the heat can be reduced by 40-20%. Therefore, the service life of AC LED is longer than that of DC LED.


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