Using Application Loss Analysis as a Figure of Merit for MOSFET Selection

Inhalt:
This paper analyses the considerations that go into the selection of power MOSFETs for switching applications. Choosing the lowest available Rdson almost always results in more expensive and inefficient solutions, particularly in high voltage switching circuits used in AC-DC converters. Comparing Figures of Merit (FOM), either the traditional Rdson x Qg product or its variants with added parameters, does not lead to the optimum solution either. It is proposed that a simplified loss equation be derived as a weighted sum of relevant MOSFET parameters and used as an application specific FOM. The process is illustrated using the high power PFC converter as an example. It is demonstrated that different MOSFETs, with identical Rdson x Qg FOM, can have different performances based on their individual parameters and operating conditions. Analytical results are compared with data taken on a 1500 W PFC unit with power MOSFETs based on different technology platforms.