Improving system reliability using FRFET® in LLC resonant converters

The trend in power converters is towards increasing power densities. In order to achieve this goal, it is necessary to reduce power losses, overall system size and weight by increasing the switching frequency. High reliability is also very important for todaypsilas switched mode power supplies. The zero-voltage-switching (ZVS) or zero-current-switching (ZCS) topologies that allow for high frequency switching while minimizing the switching losses are of interest. The ZVS topology operating at high frequency can improve the efficiency as well as reduce the size of the application. It also reduces the stress on power switches and therefore improves the reliability. LLC resonant half bridge converters are becoming a popular topology since they can provide these benefits. Now, it is widely accepted for many applications from high-end servers even to flat panel display power supplies. But the ZVS bridge topologies including LLC resonant half bridge require a MOSFET with fast reverse recovery body diode for better reliability. This article shows potential failure modes of power MOSFET in LLC resonant half bridge converters and proposes a solution for this. An enhanced FRFET^reg, power MOSFET with fast recovery body diode, provides higher reliability at the same performance.