App note: Power transistor safe operating area – special considerations for switching power supplies

App note from ON Semiconductors about less common transistors stresses when used on switching power supplies. Link here (PDF)

The power transistor, in today’s switching power supply, exists in an environment which is quite hostile to semiconductors. Large currents, large voltages, high temperature, high frequency, and low impedance sources add up to something close to the worst of all possible worlds for the transistor.
Given this type of environment, it is not surprising to find that keeping transistor stresses within acceptable limits can be quite a challenge. Transistors designed and specified specifically for switching power supplies help, but do not in themselves guarantee a reliable design. Very often, reliability is determined by the more subtle aspects of how stress imposed by the power supply relates to transistor safe operating area.

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