Abstract: In the basic DC/DC converter, high-voltage step-up capacity is limited by the parasitic parameters of the circuit and components. This paper presented the idea of putting a "coat" on the basic DC/DC converters, and proposed a family of "coat circuits" for various basic DC/DC converters. Due to the fact that there was no active switch in "coat circuit", the control and drive circuit of the basic DC/DC converters is not change. The proposed "coat circuit" could also reduce the voltage stress of the switching components, and the device stress of the proposed circuit was unity, which made the device selection easier and lower the effect caused by device stress inconsistency. Taking the Cuk converter as an example, the working principle and performance characteristics of the converter were analyzed in detail. Finally, the effectiveness of the proposed method was verified by the experimental results of a 300W prototype.