Bi-directional HEMT/GaN half-bridge circuit

1. A half-bridge circuit comprising:

an input voltage terminal operable to receive an input voltage;

a first bi-directional switch;

a second bi-directional switch connected in series with the first bi-directional switch, wherein the first and second bi-directional switches are connected to the input voltage terminal such that the input voltage is provided across the first and second bi-directional switches; and

a controller operable to turn the first and second bi-directional switches ON and OFF such that a desired voltage is provided at an midpoint node positioned between the first bi-directional switch and the second bi-directional switch,

wherein the first bi-directional switch and the second bi-directional switch are high electron mobility transistors structured to allow for conduction in two directions when ON and to prevent conduction in any direction when OFF.

2. The half-bridge circuit of claim 1 , wherein the first bi-directional switch and the second bi-directional switch are gallium nitride type transistors.

3. The half-bridge circuit of claim 2 , wherein the input voltage terminal further comprises a positive terminal and a negative terminal and the input voltage is an AC voltage, and

wherein the first and second bi-directional switched are connected between the positive terminal and the negative terminal of the input voltage terminal.

4. The half-bridge circuit of claim 3 , wherein the first and second bi-directional switches are structured such that they do not include internal diodes.

5. The half-bridge circuit of claim 4 , wherein the midpoint node is connected to a load and the desired voltage is provided to the load based on the ON/OFF status of the first and second bi-directional switches.

6. The half-bridge circuit of claim 5 , further comprising:

a transformer connected between the midpoint node and the load; and

a rectifier bridge connected to a secondary coil of the transformer and connected to the load such that the load is magnetically isolated from the midpoint node.

7. The half-bridge of claim 6 , wherein a primary coil of the transformer is connected to the midpoint node and the secondary coil is connected to the rectifier bridge such that a DC output voltage is provided to the load.

8. The half-bridge of claim 5 , further comprising a zero crossing circuit operable to determine when the voltage at the midpoint node crosses zero.

9. The half-bridge of claim 8 , wherein the zero crossing circuit is positioned in the controller and provides a zero detect signal indicating when the voltage at the midpoint node crosses zero.

10. The half-bridge of claim 9 , wherein the first and second bi-directional switches are turned ON by the controller based on the zero detect signal provided from the zero crossing circuit.

11. A half-bridge circuit comprising:

an input voltage terminal operable to receive an input voltage;

first and second bi-directional high electron mobility transistors (HEMTs) connected in a totem pole configuration directly across said input voltage terminal;

a control circuit operable to turn said first and second bi-directional HEMTs ON and OFF individually such that a desired voltage is provided at a node positioned between said first and second bi-directional HEMTs, and

wherein said first and second bi-directional HEMTs are structured to allow for conduction in two directions when ON and to prevent conduction in any direction when OFF without external diodes connected across their terminals.

12. The half-bridge circuit of claim 11 , wherein said first and second bi-directional HEMTs comprise III-nitride devices.

13. The half-bridge circuit of claim 11 , wherein said first and second bi-directional HEMTs are comprised of gallium nitride (GaN).

14. The half-bridge circuit of claim 11 , wherein the input voltage is an AC voltage and said first and second bi-directional HEMTs are connected between a positive terminal and a negative terminal of said input voltage terminal.

15. The half-bridge circuit of claim 11 , wherein the first and second bi-directional HEMTs are structured such that they do not include internal diodes.

16. The half-bridge circuit of claim 15 , further comprising:

a transformer connected between said node and a load; and

a rectifier bridge connected to a secondary coil of said transformer and connected to said load such that said load is magnetically isolated from said node.

17. The half-bridge of claim 16 , wherein a primary coil of said transformer is connected to said node and said secondary coil is connected to said rectifier bridge such that a DC output voltage is provided to said load.

18. The half-bridge of claim 11 , further comprising a zero crossing circuit operable to determine when a voltage at said node crosses zero.

19. The half-bridge of claim 18 , wherein said zero crossing circuit is included in said control circuit and provides a zero detect signal indicating when said voltage crosses zero.

20. The half-bridge of claim 19 , wherein said first and second bi-directional HEMTs are turned ON by said control circuit based on said zero detect signal.