Voltage step-up DC/DC converters are widely used in different applications. Although well investigated, the latest versions, supplemented with an additional quasi-Z-source (qZS) network coupled with a conventional inverter allowing some new properties to be obtained, need further research. This paper presents a comparative study with the aim to obtain objective parameters and characteristics of the converters with classical architecture and with a qZS-network. The comparison is based on the boundary case between the continuous and the discontinuous current. The influence of the internal resistance of the voltage source on the converter performance is discussed.