Method for measuring the mean junction temperature of alternating current light-emitting diodes

Abstract

A new technique is developed to measure the mean junction temperature during ac operation of alternating current light-emitting diodes (ac LEDs). In general, the ac electrical system supplies power at a fixed root-mean-square voltage (Vrms) but the current may vary during operation. The ac LED begins to function after the instantaneous voltage rises above a certain threshold. Both the theoretical and experimental results show that the threshold current under the threshold voltage input increases linearly with temperature. The mean temperature of the ac LED increases from the ambient temperature to a quasi-steady state under ac operation. The mean junction temperature at the quasi-steady state can be determined by using the linear temperature dependence of the threshold current and measuring the threshold currents at both the initial and quasi-steady states. After the junction temperature of an ac LED is determined, the thermal resistance from the junction to the lead frame can also be calculated by definition of the thermal resistance. The thermal resistance of an ac LED under ac operation, calculated by the present method, is very close to that measured under dc operation by the conventional forward voltage method.

A Numerical Model for Studying Multimicrochip and Single-Chip LEDs With an Interdigitated Mesa Geometry

“…A system based on the forward-voltage method [36], [39] has been constructed to measure the junction temperature of the present LEDs, as shown in Fig. 5.…”

“…However, the size of the LED chip is so tiny that the temperature distribution and the local current density in each layer are difficult to measure. At the present time, the junction temperature of LEDs is commonly measured by the forward-voltage method [36]- [39]. Bogdanov et al proposed a numerical model based on the finite volume method, which was used to simulate an IMPA LED and a conventional lateral injection LED [40], [41].…”

“…Nowadays, LEDs driven by alternating current (ac) are receiving much attention due to their characteristics of high voltage (HV) and low current [38], [39], [43], [44]. They are also convenient to operate in an ac utility system.…”

Numerical Study of Thermal Behavior in Alternating Current Light-Emitting Diodes

“…However, the input power of an AC LED is an alternating current, so the thermal effect is not the same as that for a DC LED. Hwu et al proposed a method for measuring the mean junction temperature of an AC LED [8]. In the present study, we apply a three-dimensional unsteady numerical model to simulate the thermal behavior of an AC LED chip.…”

Method to design alternating current light-emitting diodes luminous flux

“…Other research on AC LEDs include flickering luminescence overcoming through phosphor with appropriately persistent luminescence, controlling junctions' temperature and testing photoelectric and thermal performances etc. (Jang and Shin 2011;Shin and Jang 2012;Jayawardena et al 2011;Hwu et al 2011;Jayawardena et al 2013).…”