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Thermal Management Practical Application for
the High Power LED emitters.
A. Introduction
The thermal management design of an LED application is very important to
ensure its reliability and optimum performance. The maximum junction
temperature of the die inside the package is based on the allowable thermal
stress of the package material which can not be exceeded to avoid a
catastrophic failure of the device. The following is a brief overview of basic
thermal properties followed with examples as reference design which may
not be suitable for some practical applications due to a variety of constraints
from the system package design aspect or operating conditions.
B. The basic thermal modeling
The thermal resistance of a LED package is defined as the ratio of
temperature differences between the junction of the LED and the ambient
atmosphere over the power dissipation due to a current flowing through an
LED accompanied by a forward voltage drop across the device.
RΘ
Junction-Ambient
= (ΔT junction – Ambient) / P
d
(1)
Where
ΔT = T junction – T Ambient
P
d
= Forward current (If) * Forward voltage (Vf)
