Dimensionless Correlation between Empirical Modeling and T3ster Measurements for the Dynamic Thermal Characterization of the PWM-mode Current Driving UVLED

The measurement of the junction temperature of light emitting diodes (LEDs) has been crucial for the thermal management. It is more important for the applications of the ultra-violet light emitting diode (UVLED) with a low efficiency generating more heat and with the PWM-mode current driving at a higher peak current than the one with the DC-mode current driving. In this paper, the dynamic junction temperature of the UVLED with 365nm peak wavelength is characterized by the empirical modelling for the PWM-mode current driving modes with different duty cycles and periods using T3ster with the time-resolved measuring based on the JESD 51-14 and 51-51 for the DC-mode current driving. The PWM-mode response of the junction temperature rise and its fluctuation are normalized by the DC-mode response and its PWM-mode response respectively in terms of duty cycles (ranged from 10~90%) and periods (ranged from 0.1msec. to 1sec.). The DC-mode junction temperature rise with respect to applied dc currents can be direct measured by T3ster. Based on the DC correlation, the PWM-mode correlations with the power-exponential function of the normalized peak junction temperature rise and its fluctuation is established. With the proposed correlations, the normalized mean junction temperature rise as the average of the dynamic junction temperature rise over a period is found. The normalized thermal resistances of the peak, mean, fluctuation are inferred from the correlations. Furthermore, the maximum permissible pulse current is able to be determined based on the maximum rating of the DC junction temperature and the consideration of current crowding. Finally, the pulse density modulation (PDM) mode of current driving is also discussed. Those successful empirical modeling is helpful for the thermal design and thermal management for applications of UVLED with PWM-mode driving.