Four-switch step-down storageless converter

A switching DC-to-DC converter for providing power from a DC voltage source connected between an input terminal and a common terminal to a DC load connected between an output terminal and said common terminal, said converter comprising:

• a first switch with one end connected to said input terminal;
• a second switch with one end connected to another end of said first switch and the other end connected to the output terminal;
• a resonant capacitor with one end connected to said another end of said first switched;
• a first current rectifier switch with an anode end connected to another end of said resonant capacitor;
• a second current rectifier switch with an anode end connected to said common terminal;
• a first resonant inductor with one end connected to a cathode end of said first current rectifier switch and another end connected to output terminal;
• a second resonant inductor with one end connected to cathode end of said second rectifier and the other end connected to the other and of resonant capacitor;
• switching means for keeping said first switch ON and said second switch OFF during TON time interval, and keeping said first switch OFF and said second switch ON during TOFF time interval, where TON and TOFF are complementary time intervals within one switching operating cycle TS;
• wherein said first resonant inductor connected in series with said first switch, said resonant capacitor, said first current rectifier, and said second resonant inductor form a first resonant circuit during TON time interval with the resonant period Tr1;
• wherein said second resonant inductor connected in series with said second switch, said second current rectifier and said resonant capacitor form a second resonant circuit during TOFF time interval with the resonant interval Tr2;
• wherein a first resonant frequency fr1 of said first resonant circuit is independent of a second resonant frequency fr2 of said second resonant circuit;
• wherein said TON time interval is adjusted to one half of a first resonant period or 0.5Tr1 and said TOFF time interval is adjusted to one half of a second resonant period or 0.5Tr2 to obtain a fixed 2:1 step-down conversion ratio with zero freewheeling period.
• wherein said TON time interval is controlled by continuously reducing the ON-time interval, while keeping the OFF-time interval constant so that the freewheeling interval is continuously increasing causing the continuous decrease of the output voltage bellow 2:1 fixed step-down voltage conversion ratio.

A method for storageless switched-mode DC-to-DC step-down power conversion comprising:

• providing two controllable three-terminal switches and two rectifier switches, all having an ON-time interval DTS and an OFF-time interval (1−D)TS within a switching time period TS where D is a duty ratio of the switches;
• providing a first resonant inductor operating during said ON-time interval in series with one controllable switch, one rectifier switch, and a resonant capacitor with resonant period Tr1 and being flux-balanced within said ON-time period;
• providing a second resonant inductor operating during said OFF-time interval in series with another controllable switch, another rectifier switch, and said resonant capacitor with resonant period Tr2 and being flux-balanced within said OFF-time period;
• providing said resonant capacitor being charged from a DC source during said ON-time interval and being discharged into a DC load during said OFF-time interval;
• adjusting ON-time to be equal to Tr1 and adjusting OFF time to be equal to Tr2 so that the fixed 2:1 step-down conversion ratio is obtained with zero freewheeling interval;
• continuously reducing ON-time, while keeping the OFF-time constant so that the output voltage is continuously reduced bellow 2:1 DC voltage conversion ratio.