Smooth Pulse-Width Modulation in Quasi-Resonant Pulsed Converters Using Transistor as a Voltage-Controlled Capacitance

The problems of usage the pulse-width modulation in quasi-resonant converters are considered. Dependence of the parasitic drain-source (collector-emitter) capacitance of power transistors on applied of gate-source (base-emitter) voltage was established. A novel clarification of the mathematical model for high-power bipolar-junction and field-effect transistors taking into account parasitic capacitance changing under control voltage was developed. The possibility of using pulse-width modulation in conjunction with a quasi-resonant converter by using of bipolar-junction and field-effect transistors as a voltage-controlled capacitance for changing the natural frequency of resonant circuit was proposed. Proposed converter eliminates the main disadvantage of quasi-resonant converters and can be use in portable power supply and energy storage systems.