Thermische Stabilität und Kühlprobleme bei Leistungsgleichrichtern

Abstract

The essential features of the dimensional design of p-n rectifiers are discussed. The rectifier area must be chosen in such a way that the losses in reverse direction are small compared to the losses in forward. Otherwise thermal instability may occur as a result of the high increase of the reverse current with temperature. This requires relatively small areas and, correspondingly, high current densities. Therefore cooling has to be much more intensive than with the selenium rectifier in spite of the high efficiency of p-n rectifiers.

The danger of thermal instability decreases with increasing width of the forbidden band E _cv of the semiconductor, since the total amount of reverse current is rapidly reduced. The forward losses are only slightly dependent upon E _cv at a given current density. Therefore, with a sufficient width of the gap, its influence on the dimensions of the rectifier is not significant.