Abstract <p>Quasi–resonant converters can reduce the frequency-dependent part of energy losses, which promotes solving the problem concerning the increase in the operating frequency. A number of converter classes based on the phenomenon of quasi-resonance with switching at zero currents and voltages are known Optimal circuits thereof are constructed according to the basic topologies of pulsed pulse-width-modulation (PWM) converters by means of a simple replacement of the power switch by a resonant one. However, such converters, as a rule, use a frequency control method that has a number of disadvantages. The transition to a pulse width modulation mode with a constant switching frequency is possible only when additional key components are introduced into the circuit. Such a solution complicates both power part involved in the quasi-resonant converter, and its control system. The article is devoted to the basic topologies of step-down and step-up quasi-PWM converters that provide a natural process of resonance interruption and transition to a PWM control mode at a constant switching frequency with no use of any additional active or passive circuit components.</p>