Analysis of MOSFET failure modes in LLC resonant converter

The trend in telecom power supplies is towards increasing power density. The drive for high power density in switch mode power supplies is pushing high switching frequency. This increase in switching frequency is limited by switching losses. To minimize switching loss, soft switching techniques such as zero voltage switching (ZVS) or zero current switching (ZCS) are adapted for high switching frequency converters. LLC resonant half bridge converters become essential topology for greater efficiency and lower profile in switching power supplies. Nowadays, it is widely accepted for telecom power supplies due to many advantages. However, many power MOSFET failures are reported on LLC resonant converter. This paper analyzes failure operation modes and mechanisms of power MOSFETs in LLC resonant converters and shows root cause of the failures. A solution for these failure modes is proposed to improve the system reliability.