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According to the electronic design rules, every 10°C rise in temperature reduces the average life by 50%, so it is important to properly evaluate the thermal stress or junction temperature of the semiconductor devices.
Once junction temperature is known, another important parameter, thermal resistance (Rθ), may be calculated using the following equation: Junction temperature of LEDs and laser diodes. An LED or laser diode’s junction temperature (Tj) is a primary determinate for long-term reliability; it also is a key factor for photometry.
Junction temperature is calculated by using the above thermal resistance. ΔT j [deg.C]＝ R th (j-a) [deg.C/W] × P LOSS [W] T j = ΔT j + T a. ΔT j: Junction temperature rise. R th (j-a): Thermal resistance, junction to ambient. P LOSS: Power dissipation in semiconductor device. T j: Junction temperature.
3 Calculating the Junction Temperature When the junction-to-ambient thermal resistance ( JA) and the ambient temperature are given, you can calculate the junction temperature of the chip after calculating the power dissipated by the device, as follows: T J = P d JA + T A Where, JA = Junction-to-ambient thermal resistance T A
How to Calculate Junction Temperature (From Ambient Temperature) Junction temperature (or channel temperature) can be calculated from the ambient using the following equation. *Rth (j-a): Thermal resistance of "junction-to-ambient" varies depending on the type of circuit board.
The junction temperature can be calculated with Equation (6): $$T_J = \Psi_{JT} \times P_{DEVICE} + T_{SURFACE} $$ Where T SURFACE (°C) is the temperature on top of the package, and P DEVICE is the electrical power in the IC.
There are a number of ways of calculating the junction temperature of a device. These involve various levels of complexity from a quick hand calculation to a full three dimensional finite element analysis, with various shades of complexity between these two extremes.
