Active Voltage Spike Absorption for Synchronous Rectification MOSFETs in Half-Bridge Isolated DC-DC Converters

This paper solves the issue of turn-off voltage spikes in the secondary-side synchronous rectifiers of half-bridge power converter by applying active spike absorption schemes. The cause of turn-off voltage spike of MOSFET is analyzed, and the operation principle of active spike absorption circuit is introduced. By utilizing an absorption capacitor to store the spike energy and an extra MOSFET to release the energy to the output, the topology not only alleviate the voltage spike but also reduce the power loss caused by the absorption circuit. The active absorption circuit is built to verify its effectiveness. The original circuit and a passive absorption scheme are also set up as control groups. In full-load test, the voltage spike amplitude is far lower than the MOSFET's stress limit, and the efficiency reaches 90.73%. Test results suggest that the active scheme effectively mitigates voltage spike under heavy load condition, significantly improving load capacity of converter by 80% and achieving expected output power.