introduction
As the familiar backlight of the laptop is a combination of a large number of LED lights , the problem of chromatic aberration is becoming more and more obvious. If the LED lamp beads used are not in the same batch, it is easy to cause problems such as different wavelengths and chromatic aberrations. This problem is inevitable even if the same batch of LED lamp beads are used. For the testing of LED chips , the integrating sphere testing system is generally used.
Using the integrating sphere to measure parameters such as luminous flux, the measurement results can be more reliable. The integrating sphere reduces and removes errors caused by differences in light shape, divergence angle, and the like. Such high-precision and prudent measurement also drives LED integrating sphere manufacturers to increasingly choose higher performance power supplies in the system to power the LEDs to be tested.
LED integrating sphere test system
The LED integrating sphere is mainly used to measure the luminous efficiency, color rendering and chromatic aberration of the LED lamp, and the parameters that characterize the performance of the LED light source. In the large-volume test of the production line every day, there are two problems at present: one is how to improve the test efficiency and the other is how to better protect the LED to be tested in the measurement.
It is understood that in the current power industry, from the power supply to the LED lamp power supply to the software control system to collect back a stable voltage and current value, the total time is about 600ms, then on this basis, is there a possibility of breakthrough? The answer is yes. So what can be achieved? In fact, the power supply configured in the system to supply power to the LED to be tested plays a very important role.
LED integration ball test system schematic
1. Configure professional power supply to suppress overshoot and improve test efficiency
In the normal power supply, due to the loop response time, the power output does not reach the set output voltage value and stops outputting. Therefore, during this time, the voltage will overshoot. Excessive overshoot voltage can affect the life of the LED, and even severely break down the LED.
For low power LED lamps, the constant current operating current is typically between tens and hundreds of milliamps. When operating at a small current, the current and voltage climb speeds are reduced accordingly, sometimes the LED is lit for a period of time, even more than the time required to add the stable voltage and current values ​​from the normal supply of the LED lamp to the software control system. To be long.
In the face of the above two problems, in order to speed up the climb, improve the test efficiency, and improve the loop speed, it usually brings more serious overshoot. However, if the problem of overshoot is taken care of, the overall test efficiency will decrease. This kind of problem can be achieved by configuring the power supply for professional test LEDs. For example, the Itech IT6874A power supply can solve this problem. The following two figures are waveform diagrams of the voltage rise phase when the IT6874A DC power supply is supplied to LEDs of 80V/20mA and 80V/400mA.
Figure 1: LED (80V/20mA) IT6874A climbing time: about 80ms
Figure 2: LED (80V/400mA) IT6874A climbing time: about 50ms
As can be seen from the above figure, the Itech IT6874A DC power supply can basically meet the high-speed and no-overshoot test requirements in 100ms, while the general power supply takes about 600ms. The Itech IT6874A DC power supply will This number has increased by nearly 6 times, which is of great significance for the improvement of test efficiency.
1. Configure professional power supply to make the integrated ball test system collect more stable values
The stability of the power supply in the system is also very important when using the integrating sphere test. Stability is mainly reflected in:
(1) Error range of power supply
When performing the integrating sphere test, if the accuracy of using the power supply is higher, the measured data will tend to be true when the batch test is performed, and the deviation between the LEDs to be tested tends to be accurate. For example, if the LED lamp is tested, it is assumed that the allowable error range of the power supply readback is 20mV. When two LED lamps are measured simultaneously (theoretical rating is 350mA), the #1-LED measurement value may be 330mA, #2 - The LED measurement value may be 370mA. Assuming that the true values ​​of these two LED lights are 352 mA, it can be seen that the values ​​of 330 mA and 370 mA are far from the true value, and the performance indexes of the two LED lamps are also greatly deviated. If a higher precision power supply is used, assuming that the voltage readback value is allowed to be tested with a power supply of 10 mV, the value of the same two LED lamps may be between 342 mV and 362 mV, which is numerically close. It can more accurately reflect the performance index of a single LED lamp and the deviation range of consistency between multiple LEDs.
The Idex IT6874A series power supply has a voltage accuracy of up to five ten thousandths and a current accuracy of one thousandth. This high precision can bring more accurate test results to the test.
(2) Stability of collected values
What does the stability of the collected values ​​mean? Let me give you an example. For example, the power supply can illuminate the LED light within 400mS (the parameter of the LED to be tested is 80V/20mA), and the value of the voltage collected by the integrating sphere test system software is 80.099V. When the LED is turned off and turned on again, it is possible that the value read by the software is 82.152V. So simply using an oscilloscope, we can only see the waveform rise to the rated current and voltage values, but it does not guarantee that the value collected by the software also reaches a stable range. This will lead to the test of the performance of the LED lamp due to the instability of the power supply value in the LED mass production test. Under normal circumstances, software engineering developers will delay to 500-600ms to ensure stable values ​​during continuous read operations. Therefore, the time required for the integrating sphere test is about 600ms, instead of the 400ms measured by the oscilloscope.
The ITECH IT6874A DC power supply guarantees that the time from lighting the LED lamp to reading a stable voltage and current value is less than 150ms.
IT6874A measures LED light parameters: 60V/20mA takes about 150ms
It can be seen that it is of great significance to configure a power supply for LED testing in the LED integrating sphere test system. The ITECH IT6874A DC power supply breaks through the shortcomings of the general power supply in the LED integrating sphere test system, which can perfectly suppress the transient overshoot of the startup and greatly improve the test efficiency.
Product application:
â– Products for commercial,household,lighting
Product features:
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Standard
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