Variation of thermal resistance with input power in LEDs

Abstract

. 70.+f, 85.60.Bt, 85.60.Jb In this paper we report on the thermal analysis of high-power light-emitting diodes (LEDs) as a function of input power. The transient thermal measurement method using structure function was employed to investigate the thermal behavior of LEDs at different working conditions. It was shown that a 5 W LED package installed with four chips exhibited an increase of thermal resistance from 7.06 K/W to 8.83 K/W with the input current ranging from 50 mA to 700 mA at the ambient temperature of 25 ˚C. However, the thermal resistance for a 1 W LED package with one chip was decreased from 20.33 K/W to 19.54 K/W with the input current ranging from 50 mA to 350 mA. Based on our improved LED model, the different trends for the two packages are attributed to the difference in the power dissipated by internal series electrical resistances.

Thermal analysis of high power LEDs at different drive-in current

“…We are able to see that the thermal resistance (and partial thermal resistances) of the LED varies with varying drive-in current (input power). These results however, are different from those obtained from [12]. Besides that, this experiment is important to ensure that whether the thermal resistance of a material in an LED will/will not change with different input currents.…”

High-Resolution Tactile Imaging Sensor Using Total Internal Reflection and Nonrigid Pattern Matching Algorithm

“…Typically, in the LED operation, approximately 20% input power is converted to light and 80% to heat [37]. Heat at the junction of LED affects the overall performance of the LED in terms of light output and spectrum.…”

Measuring the thermal resistance of LED packages in practical circumstances

“…Yang reported that LED's thermal resistance varies while the temperature of heat flow path changes [13]. It mainly due to the following two reasons: First, the thermal conductivity of material changes with the temperature; second, the volume and pressure changing cause by thermal expansion and contraction.…”

“…T (z) = P h0 R 1 ln(10) exp(−10 z− 1 )10 z− 1 + P h0 R 2 ln(10) exp(−10 z− 2 )10 z− 2 (13) T (z) = P h0 R 1 ln 2 (10)[exp(−10 z− 1 )(10 z− 1 − 10 2(z− 1 ) )]…”

“…If the natural convection heat sink was employed to replace the temperature-controlled one, the capture time would be long, even up to 10 min to wait it reached steady state [12]. Secondly, given the fact that the thermal resistance shifts while the junction temperature changes [13], it is more difficult to measure the thermal resistance of LED packages working in practical circumstances such as road lamps, rather than on temperature-controlled heat sinks. Thirdly, the data processing is quite complicated.…”