High-power LED usage instructions and recommendations (2011)

LEDs have the unique advantages of long life, energy saving, and high brightness, which is why they are favored. Although the LED light source has the above advantages, it is not as magical as people say. Only by matching it with a suitable and efficient LED driving power supply , perfect anti-static measures, and correct installation process can the above advantages of the LED light source be fully utilized and utilized. In order to better play the performance of our products and ensure that there are fewer quality problems during the use of our customers, we have put forward the following suggestions for the installation and use process, for reference only:

First, suitable high efficiency LED drive power

The graph below shows the non-linear relationship between positive forward voltage drop (VF) and forward current (IF). It can be seen from the curve that when the forward voltage exceeds a certain threshold, that is, the so-called on-voltage, it can be approximated that IF rises sharply with the rise of VF; as can be seen from the figure, the high-power LED is low voltage and large current. For the light-emitting device, the current high-power LED has a maximum IF of 1A, and the VF is generally 2 to 4V. Since the optical characteristics of high power LEDs are generally described as a function of current (IF), not as a function of voltage (VF). In addition to the difference in LED production process and temperature, the forward voltage drop (VF) variation range of high-power LEDs will have relatively large fluctuations (up to 1V or more), and the VF-IF curve in the above figure shows that VF A small change will cause a large IF change; the intensity of the LED illumination is determined by the current flowing through the LED. If the current is too strong, the LED will be attenuated. If the current is too weak, the LED will be affected. Therefore, the use of constant voltage source drive can not guarantee the consistency of LED brightness, and affect the reliability and life of the LED. Therefore, high-power LEDs are usually driven by a constant current source to ensure the safety of high-power LEDs and achieve the desired luminous intensity.

The constant voltage circuit is the same as the linear voltage regulator of the power frequency transformer in the principle of driving the high power white LED. The constant voltage current limiting method is adopted, and the nonlinear VI curve characteristic of the high power white LED is not met, so in terms of performance, There is still a problem that the serial brightness of the series is unstable and the brightness of the light is inconsistent;

The constant current circuit driving method conforms to the nonlinear VI curve characteristic of the high-power white LED, avoids the current fluctuation caused by the slight fluctuation of the voltage, fundamentally solves the problem that the high-power LED series brightness is unstable, and ensures the illumination of the high-power LED. The brightness is constant. For the parallel use of high-power white LEDs, this type of circuit still cannot guarantee the uniformity of the brightness of the parallel branch LEDs. However, a plurality of constant current power sources can be used to respectively drive different parallel branch LEDs, and at the same time ensure the consistency of the parallel branch LED properties, thereby solving the problem of uniform brightness of the illumination;

In comparison, the constant current output mode is more suitable for use in the lighting field than the constant voltage mode. This type of circuit is superior in terms of energy conversion efficiency and brightness stability.

Common constant voltage drives have the following effects on the lamp bead due to excessive current fluctuations:

1. The gold wire and the pad/chip connection point are blown, and the center of the gold wire is blown, and the visual representation is an open circuit;

2. The chip burns in a large area (dead light) or the surface of the surface is burnt (light).

Second, perfect anti-static measures: LED is a semiconductor device sensitive to static electricity, and the anti-ESD capability of various chips is also different. Our company has strict control on anti-static measures in each process during the packaging process. In order to eliminate this external factor, we need your company to strengthen the prevention of static electricity during the assembly process of the finished product (especially in the dry season). The following is a table for directly generating static electricity under different conditions: (Generally, the anti-static ability of the chip human body model provided by our company is less than 2000V, and the InGaN anti-ESD with sapphire A1203 as the substrate can only reach 400V～500V, different brands. Comprehensive results of the product)

1,   Breakdown principle :

Electrostatic discharge (ESD) causes breakdown of the PN junction of the LED, which is the primary means of electrostatic hazard in the LED device packaging and application assembly industries. (ESD occurs very rapidly with very high intensity. When the discharge current flows through the PN junction of the LED, the Joule heat generated causes the local medium between the two poles of the chip PN to melt, causing a short circuit or leakage of the PN junction.)

2. The harm of static electricity to LED has the following two forms :

1. The heat generated by the instantaneous electric field or current causes the LED to be partially injured. The leakage current increases rapidly and still works, but the brightness is reduced (light decay, color temperature deviation), which seriously affects the service life of the LED;

2. The electric field or current destroys the insulation layer of the LED, causing reverse breakdown (internal P/N junction short circuit), making the device inoperable, showing a dead light.

3. Protective measures for static electricity during LED production and assembly:

I. Grounding: the grounding of the tool used, the grounding anti-static wrist strap, and the grounding of the work surface. When soldering, the anti-static low-voltage soldering iron should be used as much as possible, and good grounding should be maintained. In the assembly process, use a low-voltage DC electric screwdriver with a grounding wire (commonly known as an electric batch).

II. Storage and transshipment: Plastics, plexiglass and ordinary plastic bags are not used during storage and transportation. Workers must wear cordless static rings and gloves, anti-static clothing and anti-static shoes.

III. Regulation of temperature and relative humidity: When the humidity of the air is controlled, less than 60%, the anti-static operating system must be strengthened. (especially in the dry climate of winter) When the relative humidity is low in autumn and winter, it can be solved by humidifier or wet cloth mopping method.

V, detection and recording: form a good static test habit, and record and monitor in detail.

Third, the correct installation process (mainly for heat dissipation):

For a single LED, if the heat is concentrated in a chip with a small size and cannot be effectively exported, the temperature of the chip will rise, causing a non-uniform distribution of thermal stress, a luminous efficiency of the chip, and a decrease in the lasing efficiency of the phosphor (brightness). It becomes lower, and the chip wavelength is red-shifted to cause color temperature deviation). When multiple LEDs are densely arranged to form a lighting system, the heat dissipation problem is more serious. Therefore, solving the heat dissipation problem has become a prerequisite for power LED applications.

Based on the product characteristics and long-term aging test data experience, our company puts forward some suggestions on heat dissipation in the finished product installation, for reference only!

1. Heat-dissipating shell requirements: appearance and material: If the sealing requirements of the finished product are not high, it can directly convect with the outside air environment. It is recommended to use aluminum or copper fins with fins.

2. Effective heat dissipation surface area: For 1W high power LED white light (other colors are basically the same), we recommend the total heat dissipation surface area of ​​the heat sink to ≥ 50 square centimeters. For 3W products , it is recommended that the total heat dissipation surface area of ​​the heat sink be ≥150 square centimeters. The higher power depends on the situation and the test results. Try to ensure that the heat sink temperature does not exceed 50 °C.

3. Connection method: When connecting the high-power LED substrate to the heat sink, please ensure that the two contact surfaces are flat and the contact is good. To strengthen the bonding degree of the two contact surfaces, it is recommended to apply a layer of thermal grease on the bottom of the LED substrate or the surface of the heat sink (thermally conductive silicon) Grease thermal conductivity ≥ 3.0W / mk), do not use inferior silica gel or other bonding materials (not only can not achieve thermal conductivity, but form a thermal insulation layer).

  4. welding:  
Please pay attention to the selection of constant temperature soldering iron when soldering, the soldering temperature is 260 °C, Note: soldering temperature of the pin (4mm from the colloid) 260 degrees welding within three seconds! ! ! (When soldering, pay attention to the soldering iron must be grounded, the operator should wear an electrostatic bracelet or blow the ion fan) ; if it is overheated platform welding, you need to pay attention to the temperature and control the welding time, so as not to overheat the lens deformation and fall off (some manufacturers If you use a natural dry glue package, there will be delamination of the glue and the lens, which will break the gold wire and cause dead lights. If it is necessary to reflow solder 220-260 °, please explain with us, use high temperature lens package. Or the mold strip soft silicone package to solve the welding problem.

   Only by doing the above can we effectively ensure the service life of the LEDs provided by our company and avoid the quality problems that arise when using your finished products. If you have any suggestions or questions about the use of the lamp beads, please contact us. , our company will provide relevant technical support or advice.

The human body has static electricity, please do not touch it directly with your hands, pay attention to anti-static!

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