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Power Deviation Analysis of LED Lamps

2019/11/13

LED lighting products have a high incidence of "quality gate" events, on the one hand, the lack of industry norms and supervision, on the other hand, the weak quality awareness of the enterprise itself, design capacity, technology level defects.

In this paper, the power deviation of LED lamps out of control is taken as an example, theoretical calculation and case calculation are combined to analyze in detail the constant current accuracy of driving power supply and the influence of the positive voltage drop distribution of LED on the deviation of lamp power, for the reference of designers, in order to improve the design quality of LED products.

In recent years, various media frequently reported the unqualified incidents of LED light source and LED lamp quality inspected by national and local quality inspection departments. The high incidence of "quality gate" incidents seriously damaged the image of enterprises and the brand image of China's LED industry on the international stage. The situation is alarming.

In the unqualified test items, the actual test power of lamps does not conform to the declared power of products, which accounts for a large proportion. As early as 2010, China has issued the national standard GB / t24908-2010 performance requirements for self ballasted LED lamps for general lighting, which requires that "when the lamp works at rated voltage and rated frequency, the difference between its actual consumption power and rated power shall not be greater than 15% or 0.5W". The International Electrotechnical Commission also requires "the nominal value and actual value of electrical parameters of lamps" in Article 7 of iec62722-1 The deviation of international value shall not be greater than 10% ".

In the author's opinion, the causes of power deviation of products are as follows:

First, under the pressure of cost, the production process is cut down and the necessary product testing process is omitted. The unqualified products are not removed in the factory and flow to the market as inferior products.

Secondly, the design margin of LED lamp bead heat dissipation is insufficient, the deviation of assembly process and incoming materials causes the lamp bead to overheat, the drop of forward voltage drop (VF) is out of control, and the actual power of the lamp deviates from the lower limit.

Thirdly, the thermal stability of the driving power supply is poor, and the temperature drift of the output current is large, which directly causes the power deviation in a large range.

Fourth, in order to reduce the purchasing cost of LED lamp beads, the LED VF distribution bin was not selected according to the design requirements, resulting in the actual power consumption of LED deviated from the design center value.

Fifthly, the constant current accuracy of the selected driving power supply is low (generally 5% - 8%), and it can not adapt to the vfbin with various lamp beads.

The author thinks that the first three reasons directly reflect the poor quality awareness of the manufacturer and have little relevance to the design. This paper will not comment on them. The last two reasons have strong relevance to the precision design of the lamp driving power supply. The specific analysis is as follows:

Calculation expression based on lamp power

It is deduced that:

Pin - nominal power of lamp

p-deviation percentage

C-drive power efficiency

Design center value of forward voltage drop of u0-led lamp string

u-deviation percentage

I0-led drive current design center value

i-deviation percentage

Assuming that the accuracy of driving power (? I) is 5%, to meet the IEC power nominal requirements,? P is less than 10%, according to the expression [1], the deviation percentage (? U) of LED lamp string voltage is calculated to be about 4.8%, which means that it is necessary to strictly screen LED lamp beads VF bin, which directly causes the hidden lamp bead procurement cost to rise.

For example, the engineer selects 12 OSRAM LCW CRDD series lamp beads (VF bin table is as follows) with a design center value of 36V.

If the constant current accuracy 5% driving power supply is selected, the minimum voltage drop of lamp string is 34.27v and the maximum is 37.72v.

It is not difficult to find out the vfbin distribution table of the control lamp beads. Without the effective mix bin measures, nearly half of the lamp beads can not be used in mass production, and the purchase cost of the lamp beads increases significantly indirectly.

If the constant current accuracy is 1%, the minimum voltage drop of the lamp string is 32.79v, and the maximum value is 39.204v, which completely covers the lamp bead VF bin. There is no need for any mixed bin measures. The production cost and purchase cost are greatly reduced.

Through the comparative analysis of the above cases, it is not difficult to see that the high-precision driving power supply can effectively avoid the complex and unpredictable proportion of lamp beads mixed use in the lamp factory, greatly reduce the comprehensive cost of the system, and the "small cost" of the power supply will bring the "big profit" of the system.

LED lighting competition has become white hot, product prices continue to fall, at the expense of product quality or even against industry norms and regulations at the cost of low-cost strategy is not desirable. Under the premise of meeting the product quality requirements, LED industry practitioners must explore low-cost solutions so that ordinary people can afford and have high-quality LED lighting products.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.