Series connected buck-boost regulator

A series connected buck-boost regulator comprising:

• a control circuit;
• a transformer having a primary winding and a center-tapped secondary winding, wherein the center tap of said secondary winding is for connecting to a source voltage;
• a switching circuit controlled by said control circuit and for pulse-width-modulating the source voltage for inputting into said primary winding, with said switching circuit including four PWM switches connected in a bridge configuration with said primary winding connected to a center of said bridge, wherein each PWM switch has a diode connected in parallel;
• and
• an output circuit controlled by said control circuit and connected to said secondary winding for outputting a load voltage, with said output circuit having two pairs of two series connected output switches connected in parallel, wherein each output switch also has a diode connected in parallel;
• wherein said control circuit controls a duty cycle of said pulse-width-modulation of the source voltage and also drives said output circuit such that said output voltage can be varied in a range from a minimum voltage less than the source voltage to a maximum voltage greater than the source voltage;
• and further wherein some substantial fraction of the power input by the source voltage is not pulse-width-modulated by said switching circuit during one or more operating modes;
• and wherein said PWM switches include a first switch, a second switch, a third switch, and a fourth switch, and further wherein said output switches include a fifth switch, a sixth switch, a seventh switch, and an eighth switch,
• wherein, during said boost mode, said control circuit continuously turns on said fifth switch and said sixth switch, and further wherein said control circuit cycles through a plurality of boost states including:
• a first boost state wherein the first, fourth, and seventh switches are on and further wherein the second, third, and eighth switches are off;
• a second boost state wherein the seventh and eighth switches are on, and further wherein the first, second, third, and fourth switches are off;
• and
• a third boost state wherein the second, third and eighth switches are on and further wherein the first, fourth, and seventh switches are off;
• and wherein, during said buck mode, said control circuit continuously turns on said seventh switch and said eighth switch, and further wherein said control circuit cycles through a plurality of buck states including:
• a first buck state wherein said first, fourth, and sixth switches are on and further wherein said second, third, and fifth switches are off;
• a second buck state wherein said fifth and sixth switches are on, and further wherein said first, second, third, and fourth switches are off;
• and
• a third buck state wherein said second, third, and fifth switches are on, and further wherein said first, fourth, and sixth switches are off;
• and further wherein, during said current limiting mode, said control circuit continuously turns off said first, second, third, and fourth switches, and further wherein said control circuit cycles through a plurality of current limiting (CL) states including:
• a first CL state wherein said fifth, sixth, seventh, and eighth switches are on;
• and
• a second CL state wherein said fifth, sixth, seventh, and eighth switches are off.