In data center applications, the low voltage load typically operates under light-load conditions. Hence, the light-load efficiency of the switched tank converter (STC) is crucial for energy saving. In this paper, a hybrid soft switching control scheme is proposed to improve the light-load efficiency of STC. The proposed control technique regulates the frequency and phase shift between wing-side switches and bridge-side switches such that the converter is tuned in either ZCS or ZVS mode. At heavy load, the large current and high switching frequency make the switching loss of ZVS mode more severe than that of ZCS mode. While at light load, switching loss in ZCS mode is fixed and significant compared with the negligible switching loss in ZVS mode. The proposed control technique enables ZCS mode at heavy load and ZVS mode under light load, respectively. Hence, high efficiency over a wide load range can be achieved. Two modes of steady-state circuit analysis are briefed and the simulation model is established to verify the analysis. A hardware prototype that converts 48 V to 12 V is designed and tested. The results demonstrate that the light load efficiency can be improved remarkably using the proposed technique.