MOSFET Switching: Part I - Turn-ON, Hard Switching by MAYA CREATION

This article is trying to make sense out of confusing information regarding the behavior of a MOSFET during switching sequences, in numerous technical articles.

We are not attempting to explain the physics behind a MOSFET structure. For those interested to find more about a MOSFET structure, we recommend the SGS-Thomson technical articles mentioned in the references. The purpose of the article is to present a power supply design engineer with facts that will help design a MOSFET driving circuit, calculate the estimated losses for critical events, predict the efficiency of a power supply, estimate the junction temperature for critical components and various stresses, and ultimately, helping make decision to optimize a design.

The MOSFET switching events are analyzed for an inductive load, diode clamping circuit, the only one that applies to a switching power supply. The data sheet information or technical articles regarding resistive loads have little or no relevance to switching a MOSFET in a switch mode power supply. Also the article is considering only 500V/600V MOSFETs, most relevant and for switch mode power supplies.

Capacitors reference designators are the same as in SGS-Thomson articles. Check the references if a more detailed explanation of their significance is necessary.