This paper explores a Series-Capacitor Tapped Buck (SC-TaB) converter for regulated high voltage conversion ratio dc-dc applications targeting high efficiency and high power density. By adding one series capacitor and one auxiliary switch to the conventional tapped inductor buck converter, the proposed converter features many advantages including: (1) full soft switching; (2) reduced parasitic ringing; (3) capacitive energy buffering; (4) extended duty ratio; (5) reduced switch stress and (6) high efficiency over wide operating ranges. Experimental results of a 48V/5V, 750kHz, 100W, two-phase-interleaved dc-dc converter shows 91% peak efficiency, and above 88% efficiency over 38–58V input voltage range and 25–75W power range.