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, non-conforming products have not been eliminated in the factory, and flowed to the market in order to be good.

Second, the LED lamp bead has insufficient heat dissipation design margin. The assembly process and the deviation of the incoming material cause 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.

Third, the driving power of the lamp is poor in thermal stability, and the output current temperature drift is large, which directly causes the lamp power to deviate in a large range.

Fourth, in order to reduce the purchase cost of LED lamp beads, the LED beads Vf distribution BIN was not selected according to the design requirements, which caused the actual LED power consumption 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 diverse Vf BIN of lamp beads.

The author believes that the first three reasons directly reflect the manufacturer's weak quality awareness and have little relevance to design. This article does not comment on it. The latter two incentives are strongly related to the accuracy design of the lamp drive power supply. The specific analysis is as follows:

Calculation expression according to lamp power

Deduced:

Pin-lamp nominal power

△P-% deviation

C-drive power efficiency

U0-LED light string forward voltage drop design center value

△U-% deviation

I0-LED drive current design center value

△I-% deviation

Assuming that the drive power supply accuracy (?I) is 5%, to meet the IEC power nominal requirements, ?P is within 10%, and the percentage deviation of the LED string voltage (?U) is about 4.8 according to the expression [1] %, which means strict selection of LED lamp beads Vf BIN, directly causing the invisible lamp beads procurement costs to rise.

For example, engineers choose OSRAM LCW CRDD series lamp beads (Vf BIN table is as follows) 12 lights with design center value of 36V.

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

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

If the drive power with constant current accuracy of 1% is selected, the minimum value of the lamp string voltage drop is 32.79V and the maximum value is 39.204V, which completely covers the lamp bead Vf BIN without any BIN mixing measures. The production cost and procurement cost are greatly reduced.

It is not difficult to see from the comparative analysis of the above cases that the high-precision drive power supply can effectively avoid the trouble of the tedious and difficult to predict the proportion of lamp beads mixed use in the lamp factory, greatly reducing the overall cost of the system, and the "small price" of the power supply exchanges for the "big gains of the system" ".

LED lighting competition has become increasingly fierce, and product prices have continued to fall. Low-cost strategies at the cost of sacrificing product quality or even violating industry norms and regulations are undesirable. Practitioners in the LED industry must explore low-cost solutions under the premise of meeting product quality requirements, so that ordinary people can afford high-quality LED lighting products.