Power converters having synchronous rectifier circuits powered by auxiliary windings

A circuit comprising:

• a transformer including a primary winding extending between a first terminal and a second terminal, and further including a secondary winding extending between a third terminal and a first output terminal, and further including an auxiliary winding extending between a fourth terminal and the third terminal;
• a first switch having a first gate terminal, a first source terminal and a first drain terminal, the first drain terminal coupled to the second terminal and the first source terminal coupled to a power source;
• a second switch having a second gate terminal, a second source terminal and a second drain terminal, the second source terminal coupled to the third terminal and the second drain terminal coupled to a second output terminal;
• and
• a third switch having a third gate terminal, a third source terminal and a third drain terminal, the third drain terminal coupled to the second terminal and the second source terminal coupled to a first node of a first capacitor, a second node of the first capacitor coupled to the first terminal;
• wherein the secondary winding has a winding direction that is opposite to that of the primary winding and wherein the auxiliary winding has a winding direction that is same as that of the primary winding.

A circuit comprising:

• a transformer including a primary winding extending between a first terminal and a second terminal, and further including a secondary winding extending between a third terminal and a first output terminal, and further including an auxiliary winding extending between a fourth terminal and the third terminal;
• a first switch having a first gate terminal, a first source terminal and a first drain terminal, the first drain terminal coupled to first node of a capacitor and the first source terminal coupled to a power source, a second node of the capacitor coupled to the second terminal;
• a second switch having a second gate terminal, a second source terminal and a second drain terminal, the second source terminal coupled to the third terminal and the second drain terminal coupled to a second output terminal;
• a first winding coupled between the first terminal and the power source;
• and
• a third switch having a third gate terminal, a third source terminal and a third drain terminal, the third drain terminal coupled to the first winding and the second source terminal coupled to the first drain terminal;
• wherein the secondary winding has a winding direction that is opposite to that of the primary winding and wherein the auxiliary winding has a winding direction that is same as that of the primary winding.