LED has not only satisfied the market share of the general lighting market. With the downstream attention to some special segmentation application markets, some LED chip manufacturers have begun to target the market in the fields of ultraviolet and infrared, and continue to innovate. For this reason, the author will begin to focus more on this emerging application area and launch more series of evaluations for developing application products.
The model ES-SASFPN42D infrared chip product, which has been continuously pushed by Jingyuan Optoelectronics, has attracted attention because of “the highest laboratory record of luminous efficiency in the worldâ€. Recently we got 20 samples of this model. To find out, we will sample Incorporate this phase of testing and evaluation. In particular, the LED-FPD Engineering Technology Research and Development Center of Hong Kong University of Science and Technology, Foshan City was invited as a third-party testing agency to test sample parameters and performance.
The sample is initially in the bare state of the infrared chip, with a size of 42 mil X 42 mil and a thickness of 6.7 mil. It is a vertical structure chip, and the upper surface solder joint and the lower surface are all gold plated, as shown in Fig. 1.
Figure 1 chip appearance
The lab evaluation is based on the performance of the chip packaged on the 5050 bracket, as shown in Figure 2.
Figure 2 chip package in 5050 bracket
Basic light color performance
First, the remote spectral analysis system and the 0.3m integrating sphere (Fig. 3) were used, and five samples were randomly selected to carry out the basic test of the light color electrical parameters. The test results are shown in Table 1.
Figure 3 Remote spectrum analysis system and 0.3m integrating sphere
Table 1 Basic light color electrical parameters (@350mA)
The randomly selected five samples have an average radiated power of 316.4 mW, an electro-optic conversion efficiency of 61.00%, an average peak wavelength of 858.9 nm, and a half-wave width of 35.5 nm at a current of 350 mA.
According to the previous test results and experience, under the same operating conditions, the general infrared chip electro-optical conversion effect is maintained at about 50%, which is about 11% higher. That is to say, when the same electric power is consumed, more conventional chips can be provided. Higher brightness output. In some industries with high infrared illumination requirements, this can provide a basis for creating more efficient infrared lighting solutions.
In the performance of LED spectral energy distribution, we often use the peak wavelength and spectral half-wave width as an important reference. In general, infrared LEDs made of GaAs materials are significantly wider in wavelength distribution than LEDs made of other compound types and structures. The average peak wavelength of the sample is 858.9 nm. It is generally believed that the 850-950 nm range is already a long-wavelength infrared light. Compared with the traditional infrared chips that have been subject to wide wavelengths, there is indeed no small progress. From the peak wavelength curve corresponding to the average value of the half-wave width of 35.5nm, it can be seen that the spectral width is still relatively narrow, indicating that the color of the luminescence is relatively clear and pure, very clear.
Voltammetric characteristic curve
Five samples were randomly selected for voltammetric characteristics test, and the results are shown in Fig. 4.
Figure 4 volt-ampere characteristic curve
The performance of an LED can be described by its volt-ampere characteristics. The curve in the figure reflects the relationship between voltage and current. When the applied forward voltage is small, the current change is also small, almost zero. When it exceeds 1.2V, the current increases rapidly as the voltage increases. Large, exponential curve relationship, the operating current reaches 350mA when the voltage reaches 1.5V.
When the voltage change is small after the "dead zone voltage" is exceeded, the current varies greatly. The industry generally believes that the high-power LED operating current is 350mA, and the overcurrent problem of the LED should be considered in the state where constant current circuit power supply is required. Of course, from the curve, the sample is in a certain voltage range, and the current is in the working range, which is of considerable significance for reducing the power consumption of the LED and reducing the aging period.
Temperature change characteristics of light color electrical properties
On the basis of the remote 0.3m integrating sphere, a special water-cooling temperature control fixture (Fig. 5) is equipped to test the change of the light color and electric parameters of the sample at different temperatures. The results of the photochromic parameters of the evaluation product are shown in Figures 6-9.
Figure 5 0.3m integrating sphere (with special water cooling temperature control fixture)
1) Forward voltage-temperature variation characteristics (@350mA)
Figure 6 Forward voltage-temperature curve
2) Radiation power maintenance rate - temperature change characteristics (@350mA):
Figure 7 Radiation power maintenance rate - temperature curve
3) Electro-optic conversion efficiency - temperature change characteristics (@350mA):
Figure 8 Electro-optic conversion efficiency - temperature curve
4) Peak wavelength and half-wave width-temperature variation characteristics (@350mA):
Figure 9 Peak wavelength and half-wave width-temperature variation characteristics
It can be seen from Fig. 7 and Fig. 9 that the radiation power is attenuated by about 9% and the attenuation rate is about 0.15%/°C under the temperature change of 20 ° C to 80 ° C; the peak wavelength is red shifted with the increase of temperature. The rate of change is about 0.23 nm / ° C.
Light color performance under different currents
1) Characteristics of radiated power as a function of current:
Figure 10 Radiated power-current curve
2) Electro-optic conversion efficiency varies with current:
Figure 11 Electro-optic conversion efficiency - current curve
It can be seen from Fig. 10 to Fig. 11 that the radiated power increases linearly with the increase of the operating current, and the electro-optical conversion efficiency decreases linearly with the increase of the operating current.
High temperature and high humidity aging
Figure 12 Radiant flux maintenance rate changes with temperature
Based on time and cost considerations, we conducted aging tests in a 336 h high temperature and high humidity environment.
The aging conditions are 85 ° C & 85% RH, 350 mA current is lit. We performed the light color electrical performance test at 0h, 168h, and 336h respectively. The calculation, the radiation power maintenance rate is basically maintained at 98.8% after 168h, at a certain level. To a certain extent, this sample can be considered to have stable performance after aging.
summary:
From the beginning to the special segmentation application market, security, medical, automotive and other fields are the targets of such infrared chip products. As more and more companies participate, the product line is becoming more and more abundant, and infrared lighting technology remains. Faced with many bottlenecks that need to be broken, electro-optical conversion efficiency, wavelength width, product power consumption and stability need to be further refined. This infrared chip product has attracted attention since its release. According to the test results, it is excellent in light color performance and stability, and the light color and electric performance under temperature change conditions can be kept in a relatively small range. Fluctuations can be adapted to the needs of a variety of environments and applications.
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