A High Step-Down Buck Converter With Self-Driven Synchronous Rectifier

In this article, a new single-switch buck converter (without considering the synchronous rectifier) with extended duty cycle and continuous output current is proposed. The presented converter employs a self-driven synchronous rectifier with gate energy recovery, which leads to efficiency improvement and simplicity of the converter and the gate drive circuit. The extended duty cycle results in lower current stress of the high-side MOSFET and reduced voltage stress across the synchronous rectifier. Furthermore, the reverse recovery losses of synchronous rectifier are dramatically decreased due to the applied coupled inductors. The introduced converter also provides shoot-through protection and load protection when the high-side MOSFET remains on. In order to clamp the drain-source voltage spikes of the main switch and recover the leakage inductance energy, a lossless snubber circuit is added, which reduces the turn-off drain-source voltage and consequently decreases the turn-off switching losses of the main MOSFET. Moreover, the main switch turns on under zero current switching (ZCS), which results in efficiency improvement. A 150-W prototype of the proposed converter is implemented to verify the theoretical analysis and confirm its efficiency improvement and advantages.