This paper presents a regulated 24V-to-1V series-capacitor buck converter to achieve single-stage high step-down dc-dc power conversions with high efficiency and high power density. Many of the challenges faced by conventional buck converters are overcome by this converter topology. The switching losses and noise of all switching elements in this topology are sufficiently reduced because the voltage stress of switches is reduced to one-fourth of the input source voltage at switching periods. By taking advantage of the benefits from the series-capacitor buck converter topologies, all switching elements of the converter allow for low withstand voltage MOSFETs with low drain-source on-state resistance and low gate charge total characteristics. Further, the use of coupled inductors can achieve a small steady-state current ripple and enhance transient response to the load steps. The effectiveness of the topology is verified by a 24V-1V/20A prototype with a peak efficiency of 91.6%.