Journal of Radio Electronics. eISSN 1684-1719. 2023. 11
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DOI: https://doi.org/10.30898/1684-1719.2023.11.6

 

QUALITY CONTROL OF LED COB MATRIXES

BY THRESHOLD CURRENT

 

V.A. Sergeev1,2, I.V. Frolov1, S.A. Zaitsev3, .. Radaev1

 

1 Kotelnikov IRE RAS, Ulyanovsk Branch

432071, Russia, Ulyanovsk, Goncharova st. 48/2

2 Ulyanovsk State Technical University

432027, Russia, Ulyanovsk, Severnyy Venets 32

3 Ulyanovsk Instrument Manufacturing Design Bureau

432071, Russia, Ulyanovsk, Krymova st. 10A

 

The paper was received August 23, 2023.

 

Abstract. A description of a method for measuring the threshold current, the minimum current at which optical emission is occurs, of chips that are part of COB (chip on board) LEDs is given. The method consists in registering with a digital camera the average values of the emission intensities of the chips at three small values of the electric current and determining the threshold currents by solving a system of equations relating the measured intensities to a function approximating the P-I characteristic in the range of low currents. The measurement method was tested on commercially available COB LEDs consisting of ten series-connected chips. It was determined that the values of the threshold current of the chips differ: for the investigated samples, the coefficient of variation ranged from 2.6% to 39.2%. As a result of the tests of COB LEDs under the action of a current of 140 mA at a maximum allowable ambient temperature of 110 C for 11 days, it was found that changes in the average values of the threshold currents during tests correlate with changes in the current-voltage characteristics of the matrices measured in the voltage range from 17 to 24 V at which leakage current dominates: the threshold current increases for those matrices in which leakage current increases. The correlation coefficient between the relative changes in the leakage current and the average values of the threshold currents is 0.94. It is shown that the correlation coefficient between the magnitude of the decline in the luminous flux of the matrices during testing and the change in the average value of the threshold current is 0.96. The established strong correlations show the possibility of diagnosing the quality by the threshold current of individual chips in the composition of COB LEDs.

Key words: COB LEDs, threshold current, measurements, tests.

Financing: The work was carried out within the framework of the state task of the Kotelnikov Institute of Radioengineering and Electronics of Russian Academy of Sciences.

Corresponding author: Frolov Ilya Vladimirovich, ilya-frolov88@mail.ru

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For citation:

Sergeev V.A., Frolov I.V., Zaitsev S.A., Radaev O.A. Quality control of LED COB matrixes by threshold current. // Journal of Radio Electronics. 2023. . 11. https://doi.org/10.30898/1684-1719.2023.11.6 (In Russian)