LED lighting drive technical knowledge

The recent LED driver, concerns a high degree of practical application and product design innovations in energy-saving concept popular today, led lighting more and loved by everyone. LED lighting equipment at this stage the main problem is that the price is still relatively expensive, limiting its rapid spread, in order to make LED lighting more cost competitive, in addition to the LED itself is also very important to select the appropriate driver. LED lighting driver problem special compilation of relevant content for reference only.
    Q: structural model of the high-power products are closely connected metal casing and aluminum circuit board, housing and circuit board electrical isolation only in the aluminum plate to achieve this?
    A: Yes, this non-isolated power LED applications to pay attention to the main points. LED aluminum plate can do general isolation voltage of 4000V.
   Q: For small power LED to take power from 220 volts AC mains power using what program?
    A: The easiest way is to take power from the AC mains using capacitive current limiting buck, but the disadvantage is that LED charged, insecurity, and low power factor. The best approach is the use of switching power converters, made of isolated constant current power supply, the output current is constant and adjustable design, but also pay attention to the input power factor. The latter has a lot of mature circuit, but designers also point effort in switching power supply technology up and down the job.
    Q: In addition to constant current drive, the display screen pulse drive? Pulse drive, how to control? Drive power how calculated?
    A: Absolutely. Mirror circuit of the constant current source + PWM modulation, theoretically, the luminous efficiency can be done higher, but in fact the leakage current when the ON-OFF switching loss and OFF into consideration, efficiency is not so ideal and does not apply High-power LED driver. In addition, the LD laser diode is also used pulse drive, will become part of a new development direction is not known.
    Q: the size of the high-power LED package and drive voltage ordinary LED What's the difference?
    A: The small, high-power LEDs, the same color as forward drive voltage characteristic is the same. Different package because of its different cooling conditions, the difference between the light fades. At small power packaged LED is about the light fades in 1,000 hours to decay to 70% of high-power packaged LED decay to 70% at 10,000 hours. As indicated by the LED because of its small operating current to reduce light decay exponentially.
    Q: LED lights work properly or not, the quality is good or bad, with the lamp body heat is crucial. Cooling of high-power LED lights in the market are now using natural cooling effect is not ideal, what recommendations?
    A: The temperature protection is a must, which is the need of the product itself, and is also responsible for the customer. That the number of temperature protection is appropriate? If calculated according to the following situation: Suppose the maximum ambient temperature, the summer is 40 ° C in summer sunlight exposure under 50 ° C, 50 ° C ambient temperature is the actual, see generally high power LED specification junction temperature can withstand 120 ℃ , the thermal resistance of the chip to the aluminum plate, specifications generally recommended 10-15 ℃, the LED board to ensure that 120-15 = 105 ℃. Then, to retain temperature difference take 50 - 105 ℃ intermediate value of 77.5 ° C, general electronic components is reliable to the temperature of 85 ℃, 77 ℃ is in line with this principle. 77 ℃ start protection, significantly reduce the current 85 ℃, 90 ℃ thoroughly complete product temperature protection function is recommended. Of course, the actual product application, must surpasses this condition to much more stringent, LED highbay light can not maintain high heat for a long life.
    Q: Will the high-power LED thermal standards, and how to choose the heat?
    A: LED working temperature T1 = ambient temperature To + Ploss * Thermal Resistance RR = LED package thermal resistance Rled + LED and heat sink contact the thermal resistance Rled-link +? Heat sink thermal resistance? RLink can +? Heat sink and air heat resistance Rlink-air.
Choose the LED, the thermal resistance of the general package after the same heat sink thermal resistance and volume-related, often subject to the limitations of space, often become the focus of the thermal design LED and heat sink contact area and heat sink area in contact with air toothed, fin-shaped, etc., in order to increase the contact area of ​​the heat sink and the air, often the heat sink design. If the heat sink is installed in a small space or a fan (chassis), the need to consider the impact of heat flow, generally based on the modeling of the body parts, the use of fluid dynamics analysis to estimate the heat flow direction and speed, to calculate the air stream can take the heat.

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