LED lighting product power deviation Who has?
2019-04-23

Recently, various media frequently reported that the national and local quality inspection departments randomly checked the quality of LED light sources and LED lamps. The high-quality 'quality door' incident seriously damaged the company's own image and the brand image of China's LED industry on the international stage. The situation is alarming.


LED lighting products 'quality door' incidents are high, on the one hand, industry norms and supervision are absent, on the other hand, the company's own quality awareness is weak, design ability, process level defects, this article takes the LED lamp power deviation out of control as an example, theoretical calculation combined Case calculus, detailed analysis of the constant current accuracy of the driving power supply, the influence of the LED forward voltage drop distribution on the deviation of the lamp power, for the reference of the designer to improve the design quality of the LED product.


Recently, various media frequently reported that the national and local quality inspection departments randomly checked the quality of LED light sources and LED lamps. The high-quality 'quality door' incident seriously damaged the company's own image and the brand image of China's LED industry on the international stage. The situation is alarming.


In the unqualified test project, the actual test power of the luminaire does not match the declared power of the product. As early as 2010, China has issued the National Standard GB/T24908-2010 'Performance Requirements for Self-ballasted LED Lamps for General Lighting', Article 5.3 requires 'when the lamp is working at rated voltage and rated frequency, its actual power consumption and rated The difference in power should not exceed 15% or 0.5W'. The International Electrotechnical Commission also requires in paragraph 7 of IEC62722-1 that 'the deviation between the nominal value of the electrical parameters of the luminaire and the actual value should not exceed 10%'.


The author believes that the reasons for the product power deviation are as follows:


First, due to cost pressure, the production process cut corners and reduced the necessary product testing process. The unqualified products were not removed from the factory and shoddy to the market.


Second, the LED lamp bead heat dissipation design margin is insufficient, the assembly process, the deviation of the incoming material causes the lamp bead to overheat, and the forward voltage drop (Vf) drops out of control, causing the actual power of the lamp to deviate from the lower limit.


Thirdly, the thermal power supply of the selected driving power supply is poor, and the output current temperature drifts greatly, which directly causes the lamp power to deviate in a wide range.


Fourth, in order to reduce the procurement cost of LED lamp bead, the lamp bead purchase did not select the LED Vf distribution BIN according to the design requirements, causing the actual power consumption of the LED to deviate from the design center value.


Fifth, the optional drive power supply has a low constant current accuracy (typically 5%-8%) and cannot be adapted to the Vf BIN with various lamp beads.


The author believes that the first three reasons directly reflect the manufacturer's low quality awareness, and the design is not relevant, this article does not comment, the latter two incentives and the precision design of the lamp driving power supply have strong correlation, the specific analysis is as follows,

 

Lamp nominal power --- Pin;


Percentage deviation---∆P;


Drive power efficiency --- C;


LED lamp string forward pressure drop design center value --- U0; deviation percentage --- ∆U


LED drive current design center value --- I0; deviation percentage --- ∆I


According to the lamp power calculation expression Pin=U0, we derive ∆U=(∆P-∆I)【1】


Assume that the driving power supply accuracy (∆I) is 5%. To meet the IEC power nominal requirement, ∆P is within 10%. According to the expression [1], the LED light string voltage deviation percentage (∆U) is about 4.8. %, which means that the LED lamp bead Vf BIN must be strictly screened, which directly causes the invisible lamp bead purchase cost to climb.


For example, engineers chose the OSRAM LCW CRDD series of lamp beads (Vf BIN table below) for 12 light strings with a design center value of 36V:


LED照明产品功率偏差 谁之过?


If the constant current accuracy 5% drive power is used, the minimum voltage drop of the string is required to be 34.27V, and the maximum value is 37.72V.


Compared with the Vf BIN distribution table of the lamp bead, it is not difficult to find that nearly half of the lamp beads cannot be used in mass production without taking effective BIN measures, and the cost of lamp bead purchase is indirectly increased.


If the constant current accuracy is 1%, the minimum voltage drop is 32.79V and the maximum value is 39.204V, which completely covers the lamp bead Vf BIN. No need to mix BIN measures, the production cost and procurement cost are greatly reduced.


Through the comparison and analysis of the above cases, it is not difficult to see that the high-precision driving power supply can effectively avoid the troubles of the cumbersome and unpredictable proportion of lamp bead mixing in the lamp factory, greatly reduce the system comprehensive cost, and the 'small cost' of the power supply in exchange for the 'big gain' of the system. '.


LED lighting competition has become increasingly hot, and product prices continue to fall, and low-cost strategies at the expense of product quality and even against industry norms and regulatory requirements are not desirable. LED industry practitioners must explore low-cost solutions to meet the quality requirements of the product, so that ordinary people can afford high-quality LED lighting products.


Source: Landexpence Lighting