48V Voltage Regulator Modules (VRMs) are crucial to data center power supply. Control scheme of half-bridge current doubler rectifier (HBCDR) converter for VRM applications affects greatly on its transient responses. In this paper, a novel variable series resistance V2COT control is proposed. Variation of ESR provides both optimal steady-state and transient responses. Characteristics of HBCDR converter is analyzed and proposed control scheme is applied to it, validating its performances. Finally, a prototype is built.