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LED driver power supply design Four Problems Summary

2016-05-31 16:37:43
 
LED drive power quality is good or bad will directly affect the LED lifetime, how to do a LED drive power is LED power supply designers a top priority.
 
In the current life, in order to energy saving, LED has been a great promotion, but we need to have a power LED driver, which will directly affect the life of the LED, so how to do a LED drive power is LED power supply designers a top priority. This article describes some of the LED drive power in the hope that engineers can offer little help.
 
1, The driving circuit directly affects the life of the LED
We are talking about LED driver includes a digital driving and analog driving categories, digital driver circuit refers to the digital drive, including digital dimming control, RGB full color changing and so on. Driving means driving the analog circuit simulation, including AC constant current switching power supply, DC constant current control circuit. A drive circuit by the electronic components, including semiconductor elements, resistors, capacitors, inductors, etc. These components have life, any device failure will cause a failure of the entire or part of the circuit function failure. LED life of 5-10 million hours of 50,000 hours by the operator, continuous light, nearly six years of life. Switching power supply life is difficult to achieve six years, switching power supply market ** warranty period is typically 2--3 years, up to 6-year warranty power is military level, the price is 4-6 times the normal power supply, the general lighting plant is very difficult to accept. So LED lamps fault mostly drive circuit.
 
2, The heat problem
LED cold light source, operating junction temperature can not exceed the limit, but also to leave a margin design. The lighting is designed to consider the appearance, easy installation, a lot of problems with light, heat, etc., to strike a balance among other factors, so the overall lighting is the best. The LED lamp development is not a long time, can learn from the experience much, many designers are constantly improved. Some manufacturers use LED lighting power for the outsourcing or outsourcing, lighting designers do not know much of the power to LED heat dissipation larger space, the smaller the power supply to the cooling space. Generally good lighting design and then find a suitable power source facilities, which gives the power to bring a certain degree of difficulty matching. Often encountered inside the lamp due to a smaller space, or high internal temperatures, and low cost control, can not be assigned to the appropriate power source. Some LED lamp has a power plant research and development capabilities, at the beginning of the initial design lamps evaluate power supply design simultaneously, we can solve these problems. In the design takes into consideration the heat LED heat dissipation and power supply, the overall control of the temperature rise of the lamp, so as to design a better lamps.
 
3, The power supply design problems
A, power design. Although the LED luminous efficiency, but there are 80-85% of the heat loss, resulting in temperature rise inside the lamp 20-30 ($ 10.6626) degrees, if the room temperature of 25 degrees, the inside the lamp there is 45-55 degrees, the power supply for a long time in the high-temperature environment, to ensure that life we ​​must increase the power margin, generally left to 1.5-2 times the margin.
B, component selection. Lamps internal temperature at 45-55 degrees, the temperature inside the power supply there are about 20 degrees, the temperature near the element to reach 65-75 degrees. Some elements in high temperature parameter drift, some life will be shortened, so that the device you want to select, special attention can be used for a long time at a high temperature electrolytic capacitors and wires.
C, electrical performance design. Switching Power Supply for LED design parameters, the main parameters are constant, the size of the current depends on the brightness of the LED, if the bulk of the current error is large, the brightness of the entire batch of light uniform. And the change in temperature can cause the output current offset. Batch control error is generally within +/- 5%, in order to ensure uniform brightness of light .LED biased forward voltage drop, the power supply voltage constant current design range to include LED voltage range. A plurality of LED series using time series multiplied by the number of minimum pressure drop lower voltage, maximum voltage drop multiplied by the number of tandem upper limit voltage, constant current power supply voltage range slightly wider than this range, upper and lower limits of each general 1-2V left margin.
D, PCB layout design .LED lighting power left to smaller sizes (except external power supply), so the PCB design requirements higher, factors to be considered, too. Enough to stay a safe distance, requiring the input and output isolated power primary circuit and secondary circuit voltage requirements 1500-2000VAC, at least enough to stay on the PCB 3MM distance. If the metal shell lamps, the entire power distribution board should also consider the safety distance and high-pressure part of the housing. If no space is necessary to ensure a safe distance from the case to use other measures to ensure that the insulation, such as punch holes in the PCB, add insulation paper, insulation potting glue. Further layout must also consider the heat balance, the heating element to be evenly distributed, not centralized place, to avoid local temperature. Electrolytic capacitors away from heat, slow aging and prolong life.
E, certification issues. Currently no standard for LED lamps, the relevant state departments are studying the development of the domestic sales of certified reference lamp lighting fixture standards, export is to do CE or UL certification, and some reference to LED lighting standards abroad do. So for this situation, switching power supply design to meet more of these criteria is difficult, we can meet different requirements for different certification.
 
4, Using the parameters
Purchased power mainly depends on the choice of constant current and constant voltage range. LED current value is selected as the standard current lower side. Voltage range of options should be moderate, try not to choose a large range, to avoid waste of power.

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