LED lamp power deviation analysis

The high incidence of “quality gate” incidents in LED lighting products is, on the one hand, the lack of industry standards and supervision, and on the other hand, the company’s own quality awareness, weak design capabilities, and technical level defects.

LED lamp power deviation analysis

This article takes the LED lamp power deviation out of control as an example. The theoretical calculation combined with case calculations analyzes in detail the constant current accuracy of the driving power supply. The forward voltage drop of the LED affects the deviation of the lamp power for designers’ reference to improve the design quality of LED products.

Recently, various media have frequently reported national and local quality inspection departments to spot check LED light sources and LED lamps for substandard quality incidents. The high-quality “quality gate” incident has seriously damaged the company’s own image and the brand image of China’s LED industry on the international stage.

In the non-conformity test project, the actual test power of the lamp does not match the declared power of the product. As early as 2010, China has released the national standard GB / T24908-2010 “Performance requirements for self-ballasted LED lamps for general lighting” in Article 5.3, “When the lamp works at rated voltage and rated frequency, its actual power consumption and rated The difference in power should not be greater than 15% or 0.5W “, and the International Electrotechnical Commission also required in paragraph 7 of IEC62722-2 that” the deviation between the nominal value and the actual value of the electrical parameters of the lamp should not be greater than 10%. ”

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

First, due to cost pressures, the production process cut corners and cut materials, eliminating the necessary product testing process, the unqualified products have not been removed in the factory and flowed to the market in good time.

Second, the LED lamp beads have insufficient cooling design margins. The assembly process and the deviation of the incoming materials cause the lamp beads 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.

Third, the optional drive power supply of the lamp has poor thermal stability and large output current temperature drift, which directly causes the lamp power to deviate in a wide range.

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

Fifth, the constant current accuracy of the optional drive power supply is low (usually 5% -8%), and it cannot adapt to the various Vf BINs of the lamp beads.

The author believes that the first three reasons directly reflect the manufacturer’s weak quality awareness and have little relevance to the design. This article does not review them. The last two reasons have a strong correlation with the precision design of the driving power of the lamp. The specific analysis is as follows:

Assume that the drive power accuracy (△ I) is 5%. To meet the IEC power nominal requirements, P is within 10%. According to the expression [1], the LED lamp string voltage deviation percentage (△ U) is about 4.8. %, Which means that the LED lamp beads Vf BIN must be screened strictly, which directly causes the invisible lamp bead procurement costs to rise.

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

If a constant current accuracy 5% driving power source is selected, the minimum value of the voltage drop of the string is 34.27V and the maximum value is 37.72V.

It is not difficult to find the Vf BIN distribution table of lamp beads. Without effective measures to mix BINs, nearly half of the lamp beads cannot be used in mass production, and the purchase cost of lamp beads has increased significantly indirectly.

If a constant-current precision 1% drive power source is used, the minimum value of the string voltage drop is 32.79V and the maximum value is 39.204V, which completely covers the lamp bead Vf BIN, without any measures to mix BINs. Production costs and procurement costs are greatly reduced.

It is not difficult to see through the comparative analysis of the above cases that the high-precision drive power can effectively avoid the trouble of the lamp factory’s complicated and unpredictable proportion of lamp beads mixed-use, greatly reducing the overall system cost, and the “small cost” of the power source in exchange for the “big benefit” “.

LED lighting competition has become fierce, and product prices have continued to decline. Low-cost strategies at the expense of product quality or even violation of industry norms and regulations are not desirable. Technical personnel in the LED industry must explore low-cost solutions on the premise of meeting product quality requirements so that ordinary people can afford high-quality LED lighting products.