Abstract: At present, the accuracy of constant current sources commonly used in LED lighting engineering is relatively poor and cannot be adjusted. A tunable optical drive made by using a VMOS tube not only effectively overcomes the disadvantages of using a npn transistor as a constant current source. It is also possible to adjust the brightness at will according to the different time and place of the LED lighting. The total cost of using the dimmable driver is comparable to the cost of a conventional drive.
Keywords: LED driver, constant current source, triode, dimming. Most of the LED drivers currently on the market use the characteristics of the npn transistor as a constant current source, that is, the output characteristics of the triode are very straight, so corresponding in a certain area The collector current is constant. Since the EB pole forward voltage drop is unchanged at 700 mv, the collector current Ic does not change. The number of LEDs driven by the constant current source is limited by this method. When the triode is turned on, the EB pole voltage is 700mv. When the 350mA constant current source is used, the sampling resistor is only 2Ω, and the 700mA constant current source is only 1Ω, so the small resistance value is difficult to be accurate. Moreover, the EB pole voltage of the triode is a sensitive voltage that changes with temperature. The EB pole voltage changes by about 6 mV for every 1 °C change in temperature. Using this method to make a constant current source, the constant current source has poor accuracy and cannot be Adjustment. This is a constant current source commonly used in LED lighting projects.
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In everyday life, I hope that the lighting will follow people's hobbies, and it is not too glaring to ask for the same. I have developed a dimmable driver made with a Vmos tube. First of all, it overcomes the shortcomings of using a npn transistor as a constant current source. It has nothing to do with temperature, small resistance worthy of precision, and number of LEDs driven. It can be adjusted from the all-off to the brightest like the household desk lamp, and the brightness of the LED follows the potentiometer angle of the constant current value to increase smoothly, and has the best constant current output characteristic. At present, the maximum constant current is close to 800mA. In LED series applications, one driver can drive up to 100 LEDs. When a dimming function is not needed, a fixed resistor can be used instead of a potentiometer. A constant current is required to select, allowing the constant current value to be arbitrarily selected from the range of 20 mA to 800 mA.
Application examples:
1. Fluorescent tube LED tube lamp application, as shown in Figure 1:
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2. With dimming function table lamp application, as shown in Figure 2:
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3. Industrial and mining indoor lighting and road lighting applications, as shown in Figure 3:
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4. Solar powered road lighting application, as shown in Figure 4:
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The constant current driver for solar street lamps can further improve the time-sharing power supply mode. How to supply power in time? That is, the constant current source is fully powered in the first half of the night, and the constant current source is supplied with half current or 1/3 current or 1/4 current in the latter half of the night. This constant current source is on the existing basis, plus the digital-to-analog converter part. , constitutes the constant current driver of the above functions.
Keywords: LED driver, constant current source, triode, dimming. Most of the LED drivers currently on the market use the characteristics of the npn transistor as a constant current source, that is, the output characteristics of the triode are very straight, so corresponding in a certain area The collector current is constant. Since the EB pole forward voltage drop is unchanged at 700 mv, the collector current Ic does not change. The number of LEDs driven by the constant current source is limited by this method. When the triode is turned on, the EB pole voltage is 700mv. When the 350mA constant current source is used, the sampling resistor is only 2Ω, and the 700mA constant current source is only 1Ω, so the small resistance value is difficult to be accurate. Moreover, the EB pole voltage of the triode is a sensitive voltage that changes with temperature. The EB pole voltage changes by about 6 mV for every 1 °C change in temperature. Using this method to make a constant current source, the constant current source has poor accuracy and cannot be Adjustment. This is a constant current source commonly used in LED lighting projects.
In everyday life, I hope that the lighting will follow people's hobbies, and it is not too glaring to ask for the same. I have developed a dimmable driver made with a Vmos tube. First of all, it overcomes the shortcomings of using a npn transistor as a constant current source. It has nothing to do with temperature, small resistance worthy of precision, and number of LEDs driven. It can be adjusted from the all-off to the brightest like the household desk lamp, and the brightness of the LED follows the potentiometer angle of the constant current value to increase smoothly, and has the best constant current output characteristic. At present, the maximum constant current is close to 800mA. In LED series applications, one driver can drive up to 100 LEDs. When a dimming function is not needed, a fixed resistor can be used instead of a potentiometer. A constant current is required to select, allowing the constant current value to be arbitrarily selected from the range of 20 mA to 800 mA.
Application examples:
1. Fluorescent tube LED tube lamp application, as shown in Figure 1:
2. With dimming function table lamp application, as shown in Figure 2:
3. Industrial and mining indoor lighting and road lighting applications, as shown in Figure 3:
4. Solar powered road lighting application, as shown in Figure 4:
The constant current driver for solar street lamps can further improve the time-sharing power supply mode. How to supply power in time? That is, the constant current source is fully powered in the first half of the night, and the constant current source is supplied with half current or 1/3 current or 1/4 current in the latter half of the night. This constant current source is on the existing basis, plus the digital-to-analog converter part. , constitutes the constant current driver of the above functions.
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