Traditionally, the PA (Power Amplifier) for driving antenna is connected directly to the battery. However, the power efficiency of this approach is very low especially when the PA operates under a low power condition. The low power efficiency of PA decreases run-time of battery. Recently, a voltage converter with DVS (Dynamic Voltage Scaling) technique is introduced to reduce the power loss in RF (Radio Frequency) PA. In this paper, a 50MHz voltage-mode synchronous Buck converter with a DVS function for RF PA power supplies has been designed and verified. It can improve power efficiency by tracking the output voltage of RF PA changed rapidly.