Abstract <p>An analytical calculation and analysis of the main operating intervals of a step-up quasi-PWM converter over the switching frequency period are carried out. Based on the analysis results, the conditions for the converter stable operation in the soft switching mode with voltage resonance when the power switch is turned off are determined. Based on the calculation results of the current averaged over the switching period in the resonant choke, an analytical expression for the DC voltage conversion ratio of the step-up converter is obtained. It is shown that, in the general case, the conversion ratio is a complex function of three variables: the switching frequency, the PWM control coefficient, and the load current. When selecting the load current as the parameter at a constant switching frequency, a formula for calculating the family of converter control characteristics is obtained. By selecting the control coefficient as the parameter at a constant switching frequency, a formula for calculating the family of load characteristics is obtained. Experimental results confirming the correctness of the main theoretical calculations are presented. A dual correspondence between the two basic versions of the step-up and step-down quasi-PWM converters is noted.</p>