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.