Diagrams for estimating thermal impedance for pulse current of power semiconductor devices

Abstract

Diagrams for constant pulse current of the rectangular and sinusoidal wave forms were calculated. Current frequency is limited by the amount of switching losses, the relative duration of current pulses within a period being arbitrary. where 6 = The diagrams are valid for all semiconductor components whose thermal circuit is capable of electric modelling by the serial RC-pair connection and whose forward characteristic can be represented by a line or exponential curve. An example is given for use of diagrams. It compares the results obtainable by the linear and exponential approximations of the forward characteristic. 1. THE CONCEPT OF THERMAL IMPEDANCE CALCULATION FOR PULSE CURRENT Figure 1 clarifies the definition of thermal impedance for pulse current /1/ Thermal impedance for pulse current Z (t') differs from the thermal impedance for constant current (i.e. thermal resistance) Rth by addend ARth(t') th The relative thermal resistance increment of the vth RC-pair of the electrical model of the device's thermal circuit, Fig. 2 , due to pulse current is A 'Vt A V , P V M 6.1.4