Load Current and Cooling of Diodes and Thyristors

Abstract

Unlike the previous chapters which have dealt with the physics and technology of power semiconductor devices, Chaps. 10, 11, and 12 deal with their use in electronic circuits. Chapter 10 first introduces the role of the forward current-voltage characteristic and the forward voltage drop, then the role of the reverse current-voltage characteristic; it also analyses the energy loss and the power loss of diodes and thyristors. Knowledge of dynamic components of power loss (at turn on and turn off) makes it possible to explain the frequency dependence of diode and thyristor current rating. Another part of the exposition is devoted to the determination of the average power loss P AV of a diode or a thyristor, which is decisive for determining thermal flow and device cooling. There are typical examples of calculations of cooling the power semiconductor devices in the mode of continuous current loading and in the mode of pulse current loading. The calculations are made much easier by the introduction of the notions of thermal resistance and transient thermal resistance. The conclusion of Chap. 10 is devoted to the surge current rating of diodes and thyristors which, unlike commercial power devices and equipment, has a completely specific character and calls for special attention.