High efficiency resonant switching converters

A DC to DC flyback converter for supplying power derived from an input voltage source to one or more output terminals, comprising:

• a transformer which isolates the one or more output terminals from the input voltage source, said transformer having a primary winding;
• a first semiconductor switch that, when ON, electrically couples said primary winding with the input voltage source;
• a resonant capacitor;
• a second semiconductor switch that, when ON, electrically couples said resonant capacitor with said primary winding;
• and
• control circuitry having means for alternately turning said first switch ON for a period of time T.sub.ON and OFF for a period of time T.sub.OFF, respectively, and means for alternately turning said second switch ON for a period of time T.sub.D2 and OFF for a period of time T.sub.D3, respectively, wherein each second switch ON time period T.sub.D2 commences after a time delay T.sub.D1 following each instance said first switch is turned ON, and wherein said time period T.sub.D2 is limited to the time required to discharge said resonant capacitor.

A DC to DC power converter for supplying power derived from an input voltage source to an output voltage terminal, comprising:

• a transformer which isolates the output voltage terminal from the input voltage source, said transformer having a primary winding, a flyback-secondary winding and a forward-secondary winding, respectively;
• a load-side inductor electrically coupled in series with said forward-secondary winding;
• and
• a load-side storage capacitor electrically coupled with said flyback-secondary winding, said inductor and capacitor connected in parallel across said output voltage terminal.

A DC to DC flyback converter for supplying power to one or more output terminals from an input voltage source, comprising:

• a first transformer which isolates the one or more output terminals from the input voltage source, said transformer having a primary winding;
• a first semiconductor switch that, when ON, electrically couples said primary winding with the input voltage source;
• a resonant capacitor;
• a second semiconductor switch that, when ON, electrically couples said resonant capacitor with said primary winding;
• control circuitry having means for alternately turning said first switch ON and OFF according to a first selected duty cycle and means for alternately turning said second switch ON and OFF according to a second selected duty cycle, wherein said second duty cycle is selected such that said second switch is turned ON only so long as required to discharge said resonant capacitor;
• and
• start-up circuitry having means including a first semiconductor switch to connect a voltage supply for said control circuitry to the input voltage, said connection being maintained from start-up by means including a second semiconductor switch and a comparator until said voltage supply is charged by the input voltage to a first selected voltage level and then discontinued until said voltage supply drops below a second selected voltage level, wherein said second switch is controlled by an output signal from said comparator and said first switch is controlled by said second switch.