In this paper, based on the switching cell approach, a unified steady state analysis for families of soft-switching DC-DC converters with complete unified design equations will be presented. The concept of the unified approach and step by step procedure for a generalized process are discussed and applied to selected soft-switching families such as zero-voltage-switching (ZVS) and zero-current-switching (ZCS)-quasi-resonant converter families, ZVS-clamped voltage quasi-square-wave (QSW) family, ZCS-clamped-current (CC) QSW family, and zero-voltage-transition and zero-current-transition pulse-width modulation families. Also, it has been noted that all the analyzed families have one generalized transformation table. The basic unified equations are summarized and the cell-to-cell comparison will be introduced. It will be shown that the unified analysis leads to several advantages such as improving the computer-aided analysis and design, simplified mathematical modeling, and giving more insight into the converter-cell operation.