Protection circuit to prevent a transition from ZVS mode to ZCS mode under variable frequency operation

A simple protection circuit for resonant power converters using soft switching topologies is proposed in this paper. The proposed protection circuit can protect the power MOSFET of bridge converter from abnormal condition. The circuit is designed to provide protection to a power supply for a gas discharge lamp by a sudden transition from zero voltage switching (ZVS) mode to zero current switching (ZCS) mode under variable frequency operation. Using this protection circuit, the operating frequency of the lamp driving inverter system is kept close to and on the right side of the resonant frequency and the inverter is always operated in the ZVS condition. The validity and effectiveness of the proposed circuits are verified thought experimental results.