Zero-voltage switching(ZVS)can improve the efficiency of the forward converter. However，it is difficult to achieve due to the nonlinear parasitic capacitance of the power transistors and the constantly varying load current. In this study，we proposed a novel circuit design scheme based on the critical conduction model(CRM). We used a negative high-voltage zero-over-sampling circuit to sample the forward voltage drop of the power tube diode cycle-by-cycle. A self-modifying circuit integrated in the chip automatically adjusts the dead/overlap time to realize the ZVS of the active clamped forward converter. The circuit simulation results based on the 0. 18 μm BCD process design indicate that，within the load current range of 1 – 30 A in the active clamped forward converter，the power transistor adapts to the load current and achieves ZVS. The proposed design is compatible with DC-DC converters in other topologies.