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Selecting the optimum MOSFET for off-line switching power supplies

by Marty Brown, Senior Consultant, D3 Semiconductor, Electronic Products, Jun 16 2017

Focus:
On-resistance (RDS(ON)) is not the only power MOSFET parameter that determines power supply efficiency over the full load range of a power supply. Nor does choosing the MOSFET with lowest RDS(ON) necessarily produce the highest efficiency. This article highlights both these points as it identifies the various MOSFET parameters that contribute to efficiency and which must be considered in MOSFET selection. Within this context, it compares the construction and specifications of planar MOSFETs with those of superjunction MOSFETs making the case that the latter enable better efficiency, and highlighting the dramatic improvements that superjunction MOSFETs from startup D3 Semiconductor have made versus comparably rated planar MOSFETs. But most of the article is a more general introductory explanation of the role of switching versus conduction losses in determining power supply efficiency over the load range and the associated tradeoffs.

What you’ll learn:

How to understand the importance of multiple MOSFET parameters (Ciss, Crss, and RDS(ON)) on power supply efficiency over the operating range of the power supply
How to understand the benefits of superjunction MOSFETs versus planar MOSFETs in offline switching power supply designs

Notes:
After being posted online, this article appeared in the Power Supplement in the August 2017 print edition of Electronic Products magazine.

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