This application note discusses potential failure mode and mechanism in LLC resonant converters and provides a simple and cost-effective solution to prevent failures.
The document discusses the trend towards increasing power densities in switched-mode power supplies (SMPS) by utilizing high-frequency switching topologies like Zero-Voltage-Switching (ZVS). It highlights that while LLC resonant half-bridge converters offer benefits such as wide output regulation and guaranteed ZVS, they require MOSFETs with fast reverse-recovery body diodes to ensure reliability.
The text details specific failure modes associated with these converters, particularly during the startup phase. It explains how empty capacitances at startup cause higher reverse recovery currents in the low-side switch's body diode, leading to shoot-through problems when the high-side switch turns on. This can result in device breakdown due to high dv/dt stress.
A large shoot-through current flows due to the reverse-recovery current of the low-side MOSFET's body diode, which can break down the device.
The application requires a MOSFET with a fast reverse-recovery body diode to ensure better reliability.
Unexpected failures can occur during startup, overload, and output short circuit conditions.