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LED driver power supply design of the four major issues summary

LED drive power quality will have a direct impact on LED life, so how to do a good LED driver power supply is the most important of LED power supply designers.
In the current life, in order to save energy, LED has been greatly promoted, but the LED needs to have a power-driven, its good or bad will directly affect the LED life, so how to do a LED drive power is LED power supply designer Of the top priority. This article describes some of the LED drive power supply problems, hoping to provide a little help to engineers.
1, the drive circuit directly affect the LED life
We call the LED driver, including digital and analog-driven two categories, digital drive refers to the digital circuit driver, including digital dimming control, RGB full-color changes and so on. Analog drive refers to the analog circuit driver, including AC constant current switching power supply, DC constant current control circuit. Drive circuit from the electronic components, including semiconductor components, resistors, capacitors, inductors, etc., these components have life, any one device failure will lead to the failure of the entire circuit or part of the function failure. LED life is 5-10 million hours, according to 50,000 hours count, continuous light, nearly 6 years of life. Switching power supply life is very difficult to achieve 6 years, the market ** switching power supply warranty period is generally 2-3 years to reach the 6-year warranty is the military-level power supply, the price is 4-6 times the normal power supply, the general Of the lamp factory is very difficult to accept. So the failure of LED lamps and lanterns for the drive circuit failure.
2, the heat problem
LED for the cold light source, the working junction temperature can not exceed the limit, the design should leave a margin. The lighting design to consider the appearance of beautiful, easy to install, with light, heat and many other issues, to find a balance in many factors, so that the overall lighting is the best.LED lighting development time is not long, you can learn from The experience is not much, many designs are unceasingly consummates. Some manufacturers use LED lighting for the outsourcing or outsourcing, lighting designers do not know much about the power to the cooling space LED large, less cooling space to the power supply. Generally good lighting design and then find the right power to support, so give the power of supporting a certain degree of difficulty. Often encountered due to internal space or small internal lighting, high temperature, and cost control is low, can not be assigned to the appropriate power supply. Some LED lighting factory has power research and development capabilities, in the beginning to assess the initial design of lamps, power supply design synchronization, will be able to solve the above problems. In the design of integrated consideration of LED heat dissipation and power supply, the overall control of the temperature rise of the lamp, so as to design a better lamp.
3, the power supply design problems
A, power design. Although the LED light efficiency is high, but there are 80-85% of the heat loss, resulting in the lamp interior 20-30 ($ 10.6626) degree of temperature rise, if the room temperature 25 degrees, the lamp has 45-55 degrees, power for a long time Work in high-temperature environment, to ensure that life must increase the power margin, generally left to 1.5-2 times the margin.
B, component selection. Lamp internal temperature 45-55 degrees case, the power supply internal temperature rise of 20 degrees or so, then the temperature near the component to reach 65-75 degrees. Some components in the high temperature conditions will drift, and some life will be shortened, so the device should be selected at a higher temperature for a long time to use, with special attention to electrolytic capacitors and wires.
C, electrical design. Switching power supply for LED parameter design, mainly constant current parameters, the size of the current LED determines the brightness, if the bulk current error is large, the entire batch of lights uneven brightness. And temperature changes can also cause the power supply output current offset. Usually the batch error control in the +/- 5%, in order to ensure the brightness of the same LED.LED forward voltage deviation, power supply design constant current voltage range to include LED voltage range. When multiple LEDs are connected in series, the minimum voltage drop multiplied by the serial number is the lower limit voltage, the maximum voltage drop multiplied by the serial number is the upper limit voltage, the constant current voltage range of the power supply is slightly wider than this range, the general upper and lower limits Leaving 1-2V margin.
D, PCB layout design.LED lamps left to the power of the smaller size (unless it is external power supply), so in the PCB design requirements are higher, more factors to consider. The safety distance should be sufficient to require input and output isolation of the power supply, primary circuit and secondary circuit voltage requirements 1500-2000VAC, the PCB should be left at least 3MM distance. If the metal shell of the lamps and lanterns, the layout of the entire power supply but also consider the safe part of the high-voltage and shell distance. If there is no space to ensure a safe distance, we must use other measures to ensure that the insulation, such as drilling in the PCB, plus insulation paper, potting insulating plastic. Another layout board also consider the heat balance, heating elements to be evenly distributed, can not be placed centrally, to avoid local temperature. Electrolytic capacitor away from heat, slow down aging and extend the service life.
E, certification issues. Currently there is no standard for LED lighting, national relevant departments are studying the formulation of domestic sales of lighting certification is the reference lighting standards, export is done CE or UL certification, and some reference to foreign LED lighting standards to do. So for this situation, the design of switching power supply to meet these standards at the same time is more difficult, we can only meet the different requirements for different certification.
4, the use of parameters
Buying power in the choice of mainly to see the constant current and constant voltage range. The constant current value is selected as the standard current of the LED. The choice of voltage range should be moderate, try not to choose a larger range, to avoid waste of power.

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