[Source: Gaogong LED's "LED Good Products" magazine February issue] Most of the early LEDs were only used as indicator lights and neon lights. However, in recent years, due to the rapid development of high-brightness LED related technologies, the gradual reduction of LED production costs, and the maturity of LED lighting fixtures to replace traditional lighting technology, LED lighting has been widely used under the driving force of technology thrust and market pull. A wide range of fields, including indoor and outdoor lighting, architectural lighting, automotive lighting, street lighting, portable lighting, etc., and more and more manufacturers compete to join the design and development of LED lighting.
LED light particles are the light source in lighting fixtures, and the service life of the light source is often one of the important indicators when customers purchase products. Therefore, how to make the LED light source have a long-lasting service life is an important issue. At present, the service life of LED chips can reach tens of thousands of hours, and under certain special conditions, it can even reach 50,000 to 100,000 hours. However, in addition to the LED light source, the entire LED lamp also includes an LED drive circuit and a heat sink.
Therefore, not only the service life of the LED light source will affect the service life of the LED lamp, but also the service life of the LED drive circuit is one of the important factors. Traditionally, electrolytic capacitors have been used as energy storage components in LED drive circuits. However, the service life of electrolytic capacitors is rapidly attenuated as temperature rises. Therefore, when the drive circuit uses electrolytic capacitors, its service life may be reduced. There are only thousands of hours left. When the service life of the driving circuit is only several thousand hours, even if the service life of the LED chip can reach tens of thousands of hours, before the light decay of the LED chip, the driving circuit may be destroyed first, so that the service life of the LED lamp is greatly reduced. Therefore, in order to make the LED light source have a long-lasting service life, in addition to selecting an LED light source with a long-lasting life, it is also necessary to try to extend the service life of the drive circuit.
LED usage type and drive circuit architecture
In the application of LED lighting, the types of LEDs are roughly divided into three types. The first one is LEDs with low forward voltage and high forward current, such as LEDs with forward current of 350mA, 700mA or even up to 1000mA; The second is to use LEDs with high forward voltage and low forward current, such as using dozens or even hundreds of low power LEDs in series; the third is AC LED, which itself is also from dozens or even hundreds. Low-power LEDs, but basically AC LEDs can be lit without the need for an additional driver circuit. Since these three types are quite different from each other, the LED driver circuit architecture used is also very different. At present, most of the LEDs with low forward voltage and high forward current are mainly driven circuit architectures of switching converters, such as LED driving circuits developed by Buck converters or Flyback converters. For LEDs with high forward voltage and low forward current, the common LED driver circuit architecture has the following three types: circuit architecture using current limiting resistors, circuit architecture using Current Regulation Diode (CRD), and use. The circuit architecture of the switching converter. The circuit structure of the current limiting resistor mainly adjusts the forward current flowing through the LED through the series resistor, so that no additional energy storage component is needed, the circuit itself is relatively simple, and has the advantages of small size and low cost, but The LED current varies with the input voltage and cannot be maintained at a fixed value, and the LED lamp can only be driven if the input voltage is greater than its own forward voltage.
The circuit structure of the constant current diode is mainly to adjust the forward current flowing through the LED through a series-series-pass element, and the circuit architecture also has the advantages of the circuit structure of the current limiting resistor, and It can improve the limitation that the LED current in the current limiting resistor circuit structure fluctuates with the input voltage fluctuation and cannot maintain a fixed value. However, such a circuit structure also has an LED lamp that can be driven only when the input voltage is greater than its own forward voltage. The problem. Conversely, the circuit architecture of the switching converter does not have this limitation. Because it has different circuit types, it can satisfy any situation where the input voltage is greater than, less than or equal to the output voltage. However, the circuit architecture of the switching converter requires the use of magnetic components to achieve energy transfer. Therefore, compared with the circuit structure of the current limiting resistor or the circuit architecture of the constant current diode, the overall circuit cost is relatively high and the volume is relatively large. .
At present, LEDs with high forward voltage and low forward current are used in medium and low output power, such as candle lamps of less than 5W and bulbs of GU10 or 7-8W, due to volume and price considerations. More and more manufacturers have adopted the circuit architecture of constant current diodes. However, with this circuit architecture, the most common problem is that the LED can be driven only when the input voltage is greater than the forward voltage of the LED, so the input is When AC power is supplied, when the number of LEDs connected in series is large, the LED will be driven only near the peak of the input voltage, so that the time when the LED lamp is effectively lit is shortened, which will greatly reduce the LED light. The total output lumens. In order to improve this problem, it is generally possible to increase the time during which the LED lamp is effectively illuminated by reducing the number of LEDs connected in series, or to increase the current of the LED to increase the total output lumen of the LED lamp. However, reducing the number of LEDs connected in series will cause the power consumption of the driving circuit itself to be too large, reduce the conversion efficiency of the overall circuit, increase the operating temperature of the driving circuit itself, and cause special treatment of the heat dissipation of the driving circuit; The LED current may over-current the LED lamp, which may affect the life of the LED. In view of this, this article describes an off-line thyristor linear LED driver to improve this problem.
Unfinished: For more information, please check the February issue of Gaogong LED's "LED Good Products" magazine.
LED light particles are the light source in lighting fixtures, and the service life of the light source is often one of the important indicators when customers purchase products. Therefore, how to make the LED light source have a long-lasting service life is an important issue. At present, the service life of LED chips can reach tens of thousands of hours, and under certain special conditions, it can even reach 50,000 to 100,000 hours. However, in addition to the LED light source, the entire LED lamp also includes an LED drive circuit and a heat sink.
Therefore, not only the service life of the LED light source will affect the service life of the LED lamp, but also the service life of the LED drive circuit is one of the important factors. Traditionally, electrolytic capacitors have been used as energy storage components in LED drive circuits. However, the service life of electrolytic capacitors is rapidly attenuated as temperature rises. Therefore, when the drive circuit uses electrolytic capacitors, its service life may be reduced. There are only thousands of hours left. When the service life of the driving circuit is only several thousand hours, even if the service life of the LED chip can reach tens of thousands of hours, before the light decay of the LED chip, the driving circuit may be destroyed first, so that the service life of the LED lamp is greatly reduced. Therefore, in order to make the LED light source have a long-lasting service life, in addition to selecting an LED light source with a long-lasting life, it is also necessary to try to extend the service life of the drive circuit.
LED usage type and drive circuit architecture
In the application of LED lighting, the types of LEDs are roughly divided into three types. The first one is LEDs with low forward voltage and high forward current, such as LEDs with forward current of 350mA, 700mA or even up to 1000mA; The second is to use LEDs with high forward voltage and low forward current, such as using dozens or even hundreds of low power LEDs in series; the third is AC LED, which itself is also from dozens or even hundreds. Low-power LEDs, but basically AC LEDs can be lit without the need for an additional driver circuit. Since these three types are quite different from each other, the LED driver circuit architecture used is also very different. At present, most of the LEDs with low forward voltage and high forward current are mainly driven circuit architectures of switching converters, such as LED driving circuits developed by Buck converters or Flyback converters. For LEDs with high forward voltage and low forward current, the common LED driver circuit architecture has the following three types: circuit architecture using current limiting resistors, circuit architecture using Current Regulation Diode (CRD), and use. The circuit architecture of the switching converter. The circuit structure of the current limiting resistor mainly adjusts the forward current flowing through the LED through the series resistor, so that no additional energy storage component is needed, the circuit itself is relatively simple, and has the advantages of small size and low cost, but The LED current varies with the input voltage and cannot be maintained at a fixed value, and the LED lamp can only be driven if the input voltage is greater than its own forward voltage.
The circuit structure of the constant current diode is mainly to adjust the forward current flowing through the LED through a series-series-pass element, and the circuit architecture also has the advantages of the circuit structure of the current limiting resistor, and It can improve the limitation that the LED current in the current limiting resistor circuit structure fluctuates with the input voltage fluctuation and cannot maintain a fixed value. However, such a circuit structure also has an LED lamp that can be driven only when the input voltage is greater than its own forward voltage. The problem. Conversely, the circuit architecture of the switching converter does not have this limitation. Because it has different circuit types, it can satisfy any situation where the input voltage is greater than, less than or equal to the output voltage. However, the circuit architecture of the switching converter requires the use of magnetic components to achieve energy transfer. Therefore, compared with the circuit structure of the current limiting resistor or the circuit architecture of the constant current diode, the overall circuit cost is relatively high and the volume is relatively large. .
At present, LEDs with high forward voltage and low forward current are used in medium and low output power, such as candle lamps of less than 5W and bulbs of GU10 or 7-8W, due to volume and price considerations. More and more manufacturers have adopted the circuit architecture of constant current diodes. However, with this circuit architecture, the most common problem is that the LED can be driven only when the input voltage is greater than the forward voltage of the LED, so the input is When AC power is supplied, when the number of LEDs connected in series is large, the LED will be driven only near the peak of the input voltage, so that the time when the LED lamp is effectively lit is shortened, which will greatly reduce the LED light. The total output lumens. In order to improve this problem, it is generally possible to increase the time during which the LED lamp is effectively illuminated by reducing the number of LEDs connected in series, or to increase the current of the LED to increase the total output lumen of the LED lamp. However, reducing the number of LEDs connected in series will cause the power consumption of the driving circuit itself to be too large, reduce the conversion efficiency of the overall circuit, increase the operating temperature of the driving circuit itself, and cause special treatment of the heat dissipation of the driving circuit; The LED current may over-current the LED lamp, which may affect the life of the LED. In view of this, this article describes an off-line thyristor linear LED driver to improve this problem.
Unfinished: For more information, please check the February issue of Gaogong LED's "LED Good Products" magazine.
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