This article analyzes the phenomenon of LED junction temperature changing with the circuit and environment, and proposes an improved measurement of LED junction temperature based on infrared thermal imaging method. By fitting the curve between heat transfer parameters and LED chip and packaging parameters, an LED experimental model is constructed, and junction temperature detection experiments and theoretical simulations are carried out. The results indicate that compared to traditional infrared thermal imaging methods, this method is more convenient and intuitive, and can quickly measure LED junction temperature. Finally, this article compares the LED junction temperature detection results under different experimental conditions to verify the universality of this method.
KEYWORDS: Temperature metrology, Light emitting diodes, Calibration, LabVIEW, Data acquisition, Computing systems, Luminous efficiency, LED lighting, Error analysis, Temperature sensors
In order to easily and accurately measure the junction temperature of high-power LED, this paper designs a new k-value calibration module based on LabVIEW platform, and develops an improved LED junction temperature measurement system by combining hardware equipment such as thermostat, data acquisition card, constant current source and temperature sensor, aiming at the huge workload brought by fitting the voltage temperature coefficient K under large current with small current data and the measurement error caused by self heating effect. The measurement system can measure the LED junction temperature in real time and store the required data. Compared with the measured junction temperature by forward voltage method, the maximum relative error is 1.4%, which indicates that the system has high measurement accuracy.
To solve the problems of short lifespan and double-line-frequency current ripple caused by LED driver, and reduce the number of energy processing times, a high-efficiency single-stage electrolytic-capacitor-less flicker-free Boost LED driver based on the traditional Boost circuit is proposed. The driver introduces a ripple cancellation circuit, which outputs an AC ripple cancellation voltage to offset the total voltage ripple and achieve a flicker-free LED driver. Ceramic capacitors are used instead of electrolytic capacitors to extend the life of the LED driver. 96% of the power of the LED driver is converted once, the ripple coefficient of the output voltage is less than 2%, and output capacitor Co1 and output capacitor Co2 are 100μF and 47μF ceramic capacitors respectively. Finally, an 80W experimental prototype was built to verify the feasibility of the scheme.
This paper describes a tree-based decomposition and subexpression exchange method for generating new strategically valid handwritten mathematical expressions (HMEs). This approach uses the Edmonds algorithm to extract a Minimum Spanning Tree (MST) from a directed view and groups input strokes to segment symbols and label spatial relationships between symbols and symbol pairs. By training the HME recognition model and the mathematical Language Model (LM), we aim to improve the recognition performance and generalization ability of existing state-of-the-art methods from both data enhancement and model design perspectives. By adding HMEs of different styles, complexity and difficulty levels in the training dataset in order to increase the adaptability of the system to various forms of expressions.
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