As the term suggests, the buck converter converts the high- level input voltage into low-level output voltage. The main applications of the buck converter are dc source suppliers and dc motor speed control. The advantages of the buck converter [2] include: (1) it is highly efficient, since it has a simple structure needing one MOSFET switch and without any transformers to drop the voltage, and (2) the load current rate di/dt can be limited and protected by inductance Lo. The power transistor in traditional buck converters is operated in its saturation and cut-off regions as a switching switch for controlling the duty cycle of the switch to reduce the voltage. The buck converter even improves the low efficiency shortcoming of the conventional linear converter. However, raising the switching frequency also raises the switching losses, electromagnetic interference (EMI) and switching stress [3, 4], thus reducing the volume and weight of the converter to raise the power density. Therefore, a resonant converter is proposed to solve all