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.