CN111982340B - Non-contact LED junction temperature measuring method and device - Google Patents
Non-contact LED junction temperature measuring method and device Download PDFInfo
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- CN111982340B CN111982340B CN202010886611.6A CN202010886611A CN111982340B CN 111982340 B CN111982340 B CN 111982340B CN 202010886611 A CN202010886611 A CN 202010886611A CN 111982340 B CN111982340 B CN 111982340B
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Abstract
The invention discloses a method and a device for measuring the junction temperature of a non-contact LED. The method comprises two parts of laboratory calibration and field test. The invention provides a method and a device for rapidly measuring junction temperature of a white LED during normal work by adopting blue light and red light glass and combining a selenium photocell aiming at the problems of low speed and high price of spectral distribution measured by adopting a spectrometer. The selenium photocell has high response speed, the measurement speed is hundreds of times of the spectral distribution measurement, and the test cost is low; the junction temperature is represented by two parameters of the blue light ratio and the red light ratio, and the influence of current change is eliminated. According to the invention, blue light and red light glass are adopted, and simple component combinations such as a selenium photocell and the like are combined, so that junction temperature of a white LED obtained by a GaN chip and single fluorescent powder during normal operation can be accurately represented.
Description
Technical Field
The invention relates to an LED photoelectric detection device and a method thereof, in particular to a method and a device for measuring the junction temperature of a non-contact LED by adopting blue and red optical filters.
Background
In addition to the LED light source itself, the drive current and the ambient temperature are also important factors affecting the junction temperature. The white LED is an important light source in the field of illumination and display, and has important theoretical significance and application value in researching how to measure junction temperature by adopting a non-contact method.
There is a non-contact measurement method for characterizing junction temperature by white LED blue-white ratio [ YiminGu and nadarajahnardantran.a non-contact method for determining junction temperature of phosphor-converted white LEDs ] [ C ]. spie.2004,5187: 107-:
(1) the junction temperature of the LED cannot be measured when the current and junction temperatures change simultaneously.
(2) The high-precision spectrometer is required to accurately measure the luminous spectrum distribution, and the measurement cost is high.
(3) The measurement speed and measurement environment requirements are closely related to the performance of the spectrometer.
There are many reports of non-contact measurement methods of junction temperature based on spectral distribution. For example, the patent publication No. CN111220295A entitled "automatic detection device and measurement method for non-contact measurement of junction temperature of LED lamp", the patent publication No. CN110823532A entitled "method for measuring junction temperature based on variation of LED relative spectrum with temperature", the patent publication No. CN108871605A entitled "method for characterizing AlGaInP-based LED junction temperature using relative spectrum rotator volume", the patent publication No. CN105784185A entitled "apparatus and method for measuring LED junction temperature according to variation of spectrum distribution", the patent publication No. CN104792434A entitled "apparatus and method for characterizing GaN-based LED junction temperature using centroid wavelength in combination with spectral width", the patent publication No. CN104019908A entitled "method for measuring average junction temperature of LED or LED array", the patent publication No. CN104006898A entitled "method for characterizing GaN-based LED junction temperature using weighted width", the patent with publication number CN103267588A and entitled "junction temperature testing device and method based on the variation of LED relative spectrum with temperature" requires accurate measurement of spectral distribution in the implementation process, and therefore requires a high-performance spectrometer, is suitable for scientific research in laboratories, and is not suitable for wide low-cost high-precision measurement in production and life.
Disclosure of Invention
Aiming at the defects that the conventional equipment for measuring the junction temperature of the white LED based on spectral distribution is expensive and has low measurement speed, the invention aims to provide a method and a device for quickly measuring the junction temperature of the white LED in normal work by adopting blue light and red light glass and combining a selenium photocell.
In order to achieve the purpose, the invention provides the following technical scheme:
the invention provides a non-contact LED junction temperature measuring method, which comprises the following steps:
calibration: the light source sends white light, passes through the transmission of three-color disc and gets into the photocell, the three-color disc includes transparent zone, blue region, red region, measures the photovoltage of the LED light effect on the selenium photocell that sees through the three-color disc respectively under ambient temperature T1 and T2, and the LED drive adopts pulse drive, and pulse width Δ T:
⊿t＝(5％*Ie/I)2s
in the formula IeIs the rated current of the LED, I isPulse current;
selecting a plurality of pulse current values to repeatedly measure within a preset range of the upper and lower predicted working currents of the LED to obtain a plurality of groups of data of blue-white ratio and red-white ratio, neglecting the influence of current self-heating, and obtaining an equal junction temperature chart by taking the junction temperature as the ambient temperature;
measurement: the LED emits light under an environment to be measured, the photovoltage acted on the selenium photocell through the three-color disc is measured in real time, the actual blue-white ratio and the actual red-white ratio are calculated, the coordinate point is marked on the equal junction temperature graph, the junction temperature Tj is calculated according to the following equal proportion method,
Tj＝T1+(s1/s2)(T2-T1)
where T1 and T2 are junction temperatures corresponding to the equal junction temperature lines on both sides of the blue-white ratio and the red-white ratio coordinate at the time of actual lighting, s1 is a distance from the blue-white ratio and the red-white ratio coordinate to the equal junction temperature line T1 at the time of actual lighting, and s2 is a distance between the equal junction temperature lines T1 and T2.
Further, the photovoltaic cell is a selenium photovoltaic cell.
Further, when the photovoltage transmitted through the three-color disc is measured at temperatures of T1 and T2, respectively, the number of measurements is not less than 6, and the average value of the median is selected as the final result.
Furthermore, the two temperatures T1 and T2 differ by 50 ℃.
Further, at the start of calibration, the LED light source is driven at 5% of rated power.
Further, when the ambient temperatures are respectively T1 and T2, the driving current I selects not less than 6 groups of blue-white ratio and red-white ratio data points around the predicted working current of the LED, and an isojunction temperature graph with junction temperatures of T1 and T2 is obtained on a two-dimensional graph with coordinates of the blue-white ratio and the red-white ratio.
The invention also provides a non-contact LED junction temperature measuring device which comprises an LED to be measured, a three-color disc, a selenium photocell and a voltage collector, wherein the three-color disc comprises a transparent area, a blue area and a red area, the selenium photocell is arranged on the front side of the three-color disc, the selenium photocell is arranged on the rear side of the three-color disc, the selenium photocell is connected with the voltage collector, the voltage collector is used for collecting the photovoltage penetrating through the three-color disc, and the photovoltage is transmitted to a computer through a connecting wire.
Furthermore, the three-color disc is made of round and glass materials, the selenium photocell is arranged at a position 5 +/-1 cm away from the center of the three-color disc, the distance from the color disc is 0.1-1 cm, the blue area is cobalt glass with the thickness of 1 mm, the blue light transmittance at the wavelength band of 440-. The diameter of the color disc is 10-20 cm.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method and a device for rapidly measuring junction temperature of a white LED during normal work by adopting blue light and red light glass and combining a selenium photocell aiming at the problems of low speed and high price of spectral distribution measured by adopting a spectrometer. The response speed of the selenium photocell is high, and the measuring speed is hundreds of times of that of spectral measurement; the junction temperature is represented by two parameters of a blue light ratio and a red light ratio, and the influence of current is eliminated; the cost is reduced.
Drawings
FIG. 1 is a schematic diagram showing the structure of a measuring apparatus according to the present embodiment;
FIG. 2 is a schematic structural diagram of the three-color disc of the present embodiment;
FIG. 3 is a plot of the isojunction temperature obtained during the measurement;
FIG. 4 is a flow chart of a method of the present invention;
fig. 5 is an actual isotherm of the junction temperature obtained by the measurement process in the example.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, a power supply (not shown) drives a light source to be measured, white light emitted from the light source is transmitted through a three-color disc and enters a selenium photocell, and the selenium photocell generates voltage due to photoelectric effect, and the voltage is collected by a voltage collector (such as a data collection card) and input into a computer for further processing.
A typical structure of the three-color plate is shown in fig. 2, but the structure of the three-color plate of the present invention is not limited to a circular shape, and may have other shapes. This three-colour dish can rotate, and the light that sees through three kinds of glass can satisfy selenium photocell sampling requirement.
In this embodiment, a circular three-color disk is used, the disk diameter is 10 cm, and the selenium photocell probe is positioned 5 ± 1 cm from the center of the three-color disk, 0.1-1 cm from the color disk. The blue glass is cobalt glass with the thickness of 1 mm, the blue light transmittance of 440-780 nm waveband is 90-92%, the red glass is selenium red glass with the thickness of 1 mm, the light transmittance of 630-780nm waveband is 84-88%, the selenium photocell is a 2UC6 model product of Asiscai Kabushiki, the maximum output is 0.5V, and the minimum output is 0.1 mA. The sampling frequency of the data acquisition card is 10 GHz.
The measurement principle of the invention is as follows:
the red light ratio is defined as the proportion of red light in white light, and the blue light ratio is defined as the proportion of blue light in white light. For a single phosphor-converted white LED, the red and blue ratios are calculated as follows:
wherein R is red light power, W is white light power, ηrFor red light conversion efficiency, SrThe quantum efficiency in red light. Alpha is alpha0And alpharWhite light and attenuation constant, respectively.
These coefficients are both a function of junction temperature and are current dependent. The red-to-white ratio is therefore also temperature and current dependent, i.e.:
similarly, for blue-to-white ratio:
under the condition of small current change, the blue-white ratio is a function of junction temperature, and the junction temperature can be obtained by measuring the blue-white ratio, which is the principle of measuring the junction temperature by the blue-white ratio.
When the current changes greatly, the influence of the blue-white ratio is also large, and at the moment, the junction temperature is represented by only the blue-white ratio, so that the accuracy is low.
If the blue-white ratio and the red-white ratio are adopted simultaneously, the junction temperature can be represented theoretically, the driving current can also be obtained, actually, the driving current obtained by the method has a larger error, and the junction temperature is more accurate, so that the junction temperature is represented by only using the blue-white ratio and the red-white ratio.
The method for measuring the junction temperature of the non-contact LED in this embodiment is shown in fig. 4, and includes two parts, namely laboratory calibration and field test:
laboratory calibration
0805 white LED of Nissan corporation is selected as a sample, the power is 3W, and the package is an SMD (surface mounted device) patch type.
(1) Before use, a light source is driven in a laboratory at 5% of rated power, T1 is 30 ℃, T2 is 80 ℃, rated current is 750mA, driving current is 600-900 mA, the interval is 50mA, the number of measurement times is 6, and the average value of median is selected as a final result.
(2) The pulses Δ T are respectively Δ T (5% 750/I)2The precision is microsecond, and an integer is taken.
At 30 ℃ and 80 ℃ junction temperatures, 7 blue-white ratio and red-white ratio data points are respectively measured, and the obtained iso-junction temperature graph is shown in fig. 5.
(II) field test
(1) Measurement: the lamp is lightened under an environment to be measured, and Uc1 (transparent), Uc2 (blue) and Uc3 (red) are measured in real time;
(2) and calculating Uc2 (blue)/Uc 1 (transparent) and Uc3 (red)/Uc 1 (transparent), marking the two points on an equal junction temperature chart, and obtaining the junction temperature according to an equal proportion calculation method. As shown in fig. 3.
Junction temperature Tj ═ T1+ (s1/s2) (T2-T1)
In a laboratory, constant current is adopted to drive the LED, the current is 150mA and 200mA respectively, two obtained states are marked in a graph 5, and the junction temperature is 21.4 ℃ and 32.3 ℃ respectively through mathematical calculation.
In summary, on the basis of the previous research, the junction temperature of the white LED obtained by accurately representing the GaN chip and the single fluorescent powder during normal operation is obtained by combining the blue light glass and the red light glass with simple components such as a selenium photocell (which is a metal semiconductor contact type photocell with high photoelectric sensitivity reaching 500 muA/cm 2).
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A method for measuring the junction temperature of a non-contact LED is characterized by comprising the following steps:
calibration: the light source sends white light, passes through the transmission of three-color disc and gets into the photocell, the three-color disc includes transparent zone, blue region, red region, measures the photovoltage of the LED light effect on the selenium photocell that sees through the three-color disc respectively under ambient temperature T1 and T2, and the LED drive adopts pulse drive, and pulse width Δ T:
⊿t＝(5％*Ie/I)2
in the formula IeThe rated current of the LED is I, and the pulse current is I;
selecting a plurality of pulse current values to repeatedly measure within a preset range of the upper and lower predicted working currents of the LED to obtain a plurality of groups of data of blue-white ratio and red-white ratio, neglecting the influence of current self-heating, and obtaining an equal junction temperature chart by taking the junction temperature as the ambient temperature;
measurement: the LED emits light under an environment to be measured, the photovoltage acted on the selenium photocell through the three-color disc is measured in real time, the actual blue-white ratio and the actual red-white ratio are calculated, the coordinate point is marked on the equal junction temperature graph, the junction temperature Tj is calculated according to the following equal proportion method,
Tj＝T1+(s1/s2)(T2-T1)
where T1 and T2 are junction temperatures corresponding to the equal junction temperature lines on both sides of the blue-white ratio and the red-white ratio coordinate at the time of actual lighting, s1 is a distance from the blue-white ratio and the red-white ratio coordinate to the equal junction temperature line T1 at the time of actual lighting, and s2 is a distance between the equal junction temperature lines T1 and T2.
2. The method of claim 1, wherein the photovoltaic cell is a selenium photovoltaic cell.
3. A method of non-contact LED junction temperature measurement as claimed in claim 1, wherein the photovoltage across the three color disc is measured at T1 and T2, respectively, not less than 6 times, and the median average is selected as the final result.
4. The method of claim 1, wherein the two temperatures T1 and T2 differ by 50 ℃.
5. A method of measuring the junction temperature of a non-contact LED as claimed in claim 1, wherein the LED light source is driven at 5% of rated power at the start of calibration.
6. The method as claimed in claim 1, wherein the driving current I selects not less than 6 sets of blue-white ratio and red-white ratio data points around the predicted operating current of the LED when the ambient temperature is T1 and T2, respectively, and the constant junction temperature maps with junction temperatures of T1 and T2 are obtained on the two-dimensional maps with the blue-white ratio and the red-white ratio as coordinates.
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