A method to adapt Zth-junction-to-ambient curves to varying ambient conditions

The transient temperature response to a unit power step, commonly referred to as Zth-curve, is an important thermal characteristic for semiconductor devices. Zth-junction-to-ambient curves can be found in most component data sheets and are often used to calculate the time-dependent junction temperature response to a given power pulse or profile. The influence of ambient temperature and power dissipation on Zth-JA however is often neglected in these calculations since it is not possible to provide a Zth-JA curve for each ambient temperature and power dissipation. This paper presents an algorithm based on clipping a part of the structure function which allows transforming a given Zth-JA curve such that it can be adapted to arbitrary ambient temperature and power dissipation levels.