Modeling of junction temperature and forward voltage of LED devices with externally measurable variables

Junction temperature (T
j
) and forward voltage (V
F
) of LED devices are two critical LED variables that are not easily obtained in an LED system. While T
j
affects reliability and lifetime, V
F
affects the power for a given current. This paper includes the modeling of T
j
and V
F
based on externally measurable parameters such as heatsink temperature (Ths) and LED forward current (I
F
). Based on the I–V electrical characteristics, the modeling of T
j
is related to the forward current and does not need the information of V
F
. The modeling of V
F
is associated with forward current and heat sink temperature instead of junction temperature. Designers can therefore estimate the V
F
by measuring the forward current I
F
and T
hs
, thus avoid the inconvenience of measurement of junction temperature. The established theoretical models for T
j
and V
F
are verified by testing several kinds of LEDs. Very good agreements between the theoretical and practical results have been obtained.