Power MOSFET Basics

by Vrej Barkhordarian, International Rectifier, El Segundo, Ca., Vendor website, Oct 01 2005

Focus:
This application note dissects the power MOSFET, identifying and describing the various parasitic elements within MOSFET structure, and defining the data sheet parameters associated with power MOSFETs. Parameters defined here include breakdown voltage (BVDSS); on-resistance (RDSon); transconductance (gfs); threshold voltage (Vth); diode forward voltage (VF); power dissipation (Pd); capacitance parameters such as input (Ciss), output (Coss), reverse transfer (Crss), and Miller capacitance (CGD); turn-on delay (td(on)) and turn-off delay (td(off)); and gate charge (QGS and QGD). The circuits used to measure these parameters are presented. The section on RDSon includes a graph showing how the various contributions to RDSon change as the voltage rating of the MOSFET changes. Peak diode recovery or dV/dt capability and the mechanisms for dV/dt-induced turn-on are discussed. Article begins with a discussion of the advantages of power MOSFETs over bipolar junction transistors (BJTs), but also notes MOSFET disadvantage at high breakdown voltages (>200 V). Differences in the design of planar and Trench MOSFETs are also noted.

What you’ll learn:

• How to understand the definitions and significance of the key datasheet parameters for power MOSFETs

Notes:
International Rectifier Application Note AN-1084.

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