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Four LED driver power supply design issue summary​

Release date:2015-10-24

The quality LED driver power supply will directly affect the LED life, so 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 drive, which will directly affect the LED life, so how to do a LED drive power is LED power supply designers The top priority. This article describes some of the LED driver power supply problem, engineers hope to be able to offer a little help.

1, the driving circuit directly affect the LED life

We are talking about LED driver includes two types of digital driving and analog driving and digital driving means driving digital circuits, including digital dimming control, RGB full color changing and so on. Analog circuit simulation driving means driving, 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 the failure of the entire or part of the circuit function failure. LED life is 5-10 million hours, according to 50,000 hours count, continuous light, nearly six years of life. Switching power of life is difficult to achieve 6 years, the market ** switching power supply warranty period is generally 2--3 years, up to 6-year warranty is military grade power supply, the price is 4-6 times the normal power supply, general lighting plant is very difficult to accept. So LED lamps failures are mostly drive circuit.

2, the heat problem

LED is cold light source, operating junction temperature must not exceed the limits, but also left a certain margin design. The lighting is designed to consider the appearance, ease of installation, many aspects of light, heat, etc., to find a balance point in a number of factors, such as a whole is the development of lighting fixtures .LED best time is not long, you can learn little experience, a lot of design is constantly improved. Some manufacturers use LED lighting power for the outsourcing or outsourcing, lighting designer for power know much larger space to LED heat dissipation, smaller space for heat dissipation to the power supply. 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 supply. Some LED lighting plant has a power research and development capabilities, at the beginning of the initial design lamps evaluate the power of design simultaneously, we will be able to solve the above 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, 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, 25 degrees if the temperature conditions, there are 45-55 degrees inside the lamp, the power for a long time In the high-temperature environment, to ensure the life we must increase the power margin, generally left to the 1.5-2-fold 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, and 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 LED brightness, if the bulk of the current error is large, the brightness of the entire batch of light uniform. And changes in temperature can cause the power supply output current offset. Batch error control is generally within +/- 5%, in order to ensure uniform brightness of light deviation .LED forward voltage drop, the power supply voltage range constant current design to include LED voltage range. A plurality of LED series use when multiplied by the series 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, generally upper and lower limits of each 1-2V left margin.

d, PCB layout design left lighting power .LED smaller size (except external power supply), so the PCB design on demand is higher, the factors to be considered, too. Enough to stay a safe distance, requiring the input and output isolated power supply, the primary circuit and the secondary side of the circuit requires pressure 1500-2000VAC, at least on the PCB 3MM enough to stay away. 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, potting insulating plastic. Further layout must also consider the heat balance, the heating element to be uniformly distributed, not centralized place, to avoid local temperature. Electrolytic capacitors away from heat, slow down 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 lighting fixtures certified reference standards, export is doing CE or UL certification, and some reference LED lighting standards abroad to do. So for this situation, switching power supply design to meet more of these criteria are difficult, we can only meet the different authentication requirements for different.

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 wasting power.