Understanding MOSFETSemiWell notes Understanding MOSFETs Maximum Ratings Introduction Maximum rating means maximum electrical and thermal stresses that device can be subjected to and withstand. There needs a careful thought to design system for not over maximum rating ,applied stress to device could be a permanently damaged. BVDSS(V) : drain to source voltage BVDSS is determined by resistivity and thickness of epitaxial layer. As is shown at Fig 1, BVDSS is measured at a typical current with source shortcircuited to gate and drain to source reverse biased. Unlikely bipolar transistor, there is not found second breakdown effect. High voltage MOSFET used in some application, the BVDSS of MOSFET decreases after certain period of time. So to prevent it, system should be designed to get a enough BVDSS margins. A……