[Source: "High-tech LED - Technology and Applications" October issue]
First, the question is raised
In recent years, with the continuous improvement of the manufacturing process of light-emitting diodes (LED) and the development and application of new materials, high-power LEDs of various colors have made breakthroughs. The luminous efficacy of high-brightness white LEDs has exceeded 200 lm/W. In terms of chromaticity, all colors in the visible light band have been realized, especially the emergence of power white LEDs, which has led to the application of LEDs to the high-efficiency lighting source market. Conventional LEDs use direct current (DC) as the driving power source, and must be AC/DC converted when they are powered by a general AC power source (AC). At the same time, due to the inherent characteristics of the LED current and voltage, it is often necessary to increase the voltage regulation and constant current during the conversion process. In the process of AC/DC conversion, about 10%-30% of the power consumption is lost, especially the performance of the small power conversion device is more Low, while the electrolytic capacitors used in the AC/DC conversion process make the life of the power conversion impossible to synchronize with the LED. In order to give full play to the life expectancy of LED lighting and reduce the volume of lamps, many technology companies have invested heavily in the development of ACLEDs for AC power supply to further reduce the cost of lamps and extend the service life of lamps.
Second, the structure analysis of existing AC LED
The AC LED utilizes the diode characteristics of the LED to be directly rectified by the LED. The initial solution is to use a plurality of two identical LEDs to form a simple AC LED, as shown in Figure 1.
The utilization rate of this kind of LED is only 50%. In the era of extremely high LED die prices, it is obviously impossible to enter commercial applications. In order to improve the chip utilization rate of the whole tube, some scientists use the Wheatstone bridge to design the structure design chip as shown in Figure 2. Most of the chips are lit when the AC LED is working in forward and reverse directions, but because of the LED inversion. The breakdown voltage is limited. When this scheme is used on a 110V power supply, the LEDs on the bridge arm also need 8-10, usually 9, according to the VF value of the LED, only 16 can be installed on the bridge, so this structure There are a total of 52 internal AC LEDs. In the half cycle, only 34 LEDs are illuminated, and the LED's lighting rate is only 65%. When this solution is used on a 220V power supply, the LEDs on the bridge arm also need 16-20 LEDs, usually 18, on the bridge. Only 32 can be installed, so there are a total of 104 internal AC LEDs in this structure. Since there is no constant current control circuit inside the AC LED, current limiting measures must be added during actual use to prevent fluctuations in the power supply voltage. The LED overcurrent disaster caused. Samsung's 4W ACLED is recommended to use the circuit shown in Figure 3 when it is used in a 220V power supply. In the figure, the PTC is a thermistor with a temperature of 470 at room temperature. R1, R2, and R3 are not only different in resistance, but also different in power supply and voltage. The resistance value is calculated by using the B specification of 220V. The resistance is 1.951K. The current and voltage waveforms driven by a voltage of 220V are shown in Fig. 4.
Unfinished
For more information, please refer to the October issue of "High-tech LED-Technology and Applications"
First, the question is raised
In recent years, with the continuous improvement of the manufacturing process of light-emitting diodes (LED) and the development and application of new materials, high-power LEDs of various colors have made breakthroughs. The luminous efficacy of high-brightness white LEDs has exceeded 200 lm/W. In terms of chromaticity, all colors in the visible light band have been realized, especially the emergence of power white LEDs, which has led to the application of LEDs to the high-efficiency lighting source market. Conventional LEDs use direct current (DC) as the driving power source, and must be AC/DC converted when they are powered by a general AC power source (AC). At the same time, due to the inherent characteristics of the LED current and voltage, it is often necessary to increase the voltage regulation and constant current during the conversion process. In the process of AC/DC conversion, about 10%-30% of the power consumption is lost, especially the performance of the small power conversion device is more Low, while the electrolytic capacitors used in the AC/DC conversion process make the life of the power conversion impossible to synchronize with the LED. In order to give full play to the life expectancy of LED lighting and reduce the volume of lamps, many technology companies have invested heavily in the development of ACLEDs for AC power supply to further reduce the cost of lamps and extend the service life of lamps.
Second, the structure analysis of existing AC LED
The AC LED utilizes the diode characteristics of the LED to be directly rectified by the LED. The initial solution is to use a plurality of two identical LEDs to form a simple AC LED, as shown in Figure 1.
The utilization rate of this kind of LED is only 50%. In the era of extremely high LED die prices, it is obviously impossible to enter commercial applications. In order to improve the chip utilization rate of the whole tube, some scientists use the Wheatstone bridge to design the structure design chip as shown in Figure 2. Most of the chips are lit when the AC LED is working in forward and reverse directions, but because of the LED inversion. The breakdown voltage is limited. When this scheme is used on a 110V power supply, the LEDs on the bridge arm also need 8-10, usually 9, according to the VF value of the LED, only 16 can be installed on the bridge, so this structure There are a total of 52 internal AC LEDs. In the half cycle, only 34 LEDs are illuminated, and the LED's lighting rate is only 65%. When this solution is used on a 220V power supply, the LEDs on the bridge arm also need 16-20 LEDs, usually 18, on the bridge. Only 32 can be installed, so there are a total of 104 internal AC LEDs in this structure. Since there is no constant current control circuit inside the AC LED, current limiting measures must be added during actual use to prevent fluctuations in the power supply voltage. The LED overcurrent disaster caused. Samsung's 4W ACLED is recommended to use the circuit shown in Figure 3 when it is used in a 220V power supply. In the figure, the PTC is a thermistor with a temperature of 470 at room temperature. R1, R2, and R3 are not only different in resistance, but also different in power supply and voltage. The resistance value is calculated by using the B specification of 220V. The resistance is 1.951K. The current and voltage waveforms driven by a voltage of 220V are shown in Fig. 4.
image 3
Figure 4
Unfinished
For more information, please refer to the October issue of "High-tech LED-Technology and Applications"
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