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Published byConrad Gabriel Modified about 1 year ago

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Modelling power LEDs in SPICE with selfheating taken into account Krzysztof Górecki Department of Marine Electronics Gdynia Maritime University, POLAND

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Outline Introduction Description of the model Results of calculations and measurements Conclusions

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Introduction Power LEDs are more and more frequently used for the illumination of rooms, illuminated advertisings and in motorization. The advantages of power LED are: High efficiency, low power consumption, high reliability. The properties of power LEDs (the current-voltage characteristics, the luminance and the lifetime) depend strongly on temperature. The internal temperature T j of the LED is equal to the sum of the ambient temperature T a and the rise of the temperature caused by selfheating. In order to include in analyses the influence of selfheating on the properties of the power LED it is indispensable to use special electrothermal models of this device.

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Introduction (cont.) In this paper the new compact electrothermal model of the power LED for SPICE is proposed. The correctness of this model is verified experimentally.

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Description of the model 3 components of the model: the electrical model – i(v) characteristics, the thermal model – T j (i,v) dependence, the optical model - the dependence of luminance on temperature. The network representation of this model G 1 - the normal and recombination current, G 2 - the breakdown current, R S0 - the series resistance of the diode E RS - the additional voltage drop on the series resistance, resulting from the temperature rise Detailed description of the model – see proceedings

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Results of calculations and measurements Verification of the model for the diode LXHL-BW03 produced by Luxeon The values of parameters obtained from measurements – see proceedings Results for the diode situated on the big heat-sink (R th = 9 K/W)

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Results of calculations and measurements (cont.) The influence of cooling conditions on the dc characteristics the thermal resistance R th is equal to: 105 K/W for the diode without any heat-sink, 33 K/W for the diode on the small heat-sink, 9 K/W for the diode situated on the large heat-sink.

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Results of calculations and measurements (cont.) The dependence of the relative luminance of the diode on the forward current and the voltage drop

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Conclusions The electrothermal model of the power LED proposed in this paper has a simple form, and simultaneously ensures a good agreement between the calculated and measured dc characteristics of the considered device. The results of the calculations and the measurements prove that the ambient temperature and the selfheating phenomenon strongly influence the electrical and optical characteristics of the considered device. The elaborated model makes it possible to estimate, with good accuracy, the values of the internal temperature of the investigated LED, which to a great extent decides about its reliability.

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