Power converters having synchronous rectifier circuits powered by auxiliary windings

1 . 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 gate terminal, a source terminal and a drain terminal, the source terminal coupled to the third terminal and the drain terminal coupled to a second output terminal;

a second switch coupled between the second terminal and a power source; and

a diode having an anode and a cathode, the anode coupled to the fourth terminal and the cathode coupled to a controller circuit, wherein the controller circuit is directly coupled to the third terminal, and wherein the controller circuit is directly coupled to the second output terminal; and

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.

2 . The circuit of claim 1 , wherein the controller circuit is further coupled to the gate terminal and the drain terminal.

3 . The circuit of claim 2 , wherein the controller circuit is arranged to control a voltage at the gate terminal such that when the first switch is on, the second switch is off and when the first switch is off, the second switch is on.

4 . The circuit of claim 3 , further comprising a load coupled between the first output terminal and the second output terminal.

5 . The circuit of claim 4 , further comprising a capacitor coupled in between the first output terminal and the second output terminal.

6 . The circuit of claim 1 , wherein the first switch is a gallium nitride (GaN) based transistor.

7 . 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 gate terminal, a source terminal and a drain terminal, the source terminal coupled to the third terminal and the drain terminal coupled to a second output terminal; and

a second switch coupled between the second terminal and a power source;

a capacitor coupled between the first terminal and the second terminal;

a third switch coupled between the capacitor and the second terminal;

a diode having an anode and a cathode, the anode coupled to the fourth terminal and the cathode coupled to a controller circuit, wherein the controller circuit is directly coupled to the third terminal, and wherein the controller circuit is directly coupled to the second output terminal; and

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.

8 . The circuit of claim 7 , wherein the controller circuit is further coupled to the gate terminal and the drain terminal.

9 . The circuit of claim 8 , wherein the controller circuit is arranged to control a voltage at the gate terminal such that when the first switch is on, the second switch is off and when the first switch is off, the second switch is on.

10 . The circuit of claim 7 , further comprising a load coupled between the first output terminal and the second output terminal.

11 . The circuit of claim 10 , wherein the capacitor is a first capacitor and wherein the circuit further comprises a second capacitor coupled between the first output terminal and the second output terminal.

12 . The circuit of claim 7 , wherein the first switch is a gallium nitride (GaN) based transistor.

13 . 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 gate terminal, a source terminal and a drain terminal, the source terminal coupled to the third terminal and the drain terminal coupled to a second output terminal;

a second switch coupled between the second terminal and a power source;

a third switch coupled between the second terminal and the power source;

a diode having an anode and a cathode, the anode coupled to the fourth terminal and the cathode coupled to a controller circuit, wherein the controller circuit is directly coupled to the third terminal, and wherein the controller circuit is directly coupled to the second output terminal; and

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.

14 . The circuit of claim 13 , wherein the controller circuit is coupled to the gate terminal and the drain terminal.

15 . The circuit of claim 14 , wherein the controller circuit is arranged to control a voltage at the gate terminal such that when the first switch is on, the second switch is off and when the first switch is off, the second switch is on.

16 . The circuit of claim 13 , further comprising a load coupled between the first output terminal and the second output terminal.

17 . The circuit of claim 13 , wherein the first switch is a gallium nitride (GaN) based transistor.