Switch-mode power supplies including three-level LLC circuits

1. A switch-mode power supply, comprising:

a pair of input terminals for receiving an alternating current (AC) or direct current (DC) voltage input from an input power source;

a pair of output terminals for supplying a direct current (DC) voltage output to a load;

a three-level LLC circuit coupled between the pair of input terminals and the pair of output terminals, the circuit including a first switch coupled with a first diode to define a first half-bridge and a second switch coupled with a second diode to define a second half-bridge;

a third switch coupled across the first diode and the second diode to short circuit the first diode and the second diode when the third switch is closed; and

a control circuit including a voltage-controlled oscillator (VCO), at least one flip-flop and multiple logic gates to operate the three switches with zero-voltage switching (ZVS).

2. The power supply of claim 1 , further comprising a transformer and multiple secondary diodes, wherein the transformer includes a primary winding and a secondary winding, the third switch is coupled with the primary winding, and the multiple secondary diodes are coupled with the secondary winding.

3. The power supply of claim 1 , further comprising a transformer and multiple synchronous rectifier switches, wherein the transformer includes a primary winding and a secondary winding, the third switch is coupled with the primary winding, and the multiple synchronous rectifier switches are coupled with the secondary winding.

4. The power supply of claim 3 , wherein the control circuit is coupled to operate the multiple synchronous rectifier switches with zero-voltage switching (ZVS) and zero-current switching (ZCS).

5. The power supply of claim 2 , further comprising:

a first capacitor and a first inductor coupled between the primary winding and the first half-bridge; and

a second capacitor and a second inductor coupled between the primary winding and the second half-bridge.

6. The power supply of claim 1 , further comprising:

a circuit ground, wherein the first half-bridge is coupled between the circuit ground and a first one of the pair of input terminals, and the second half-bridge is coupled between the circuit ground and a second one of the pair of input terminals; and

first and second capacitors, wherein the first capacitor is coupled between the circuit ground and the first input terminal, and the second capacitor is coupled between the circuit ground and the second input terminal.

7. The power supply of claim 6 , wherein capacitance values of the first and second capacitors are the same to divide the voltage input equally across the first and second capacitors.

8. The power supply of claim 1 , wherein only the third switch is coupled across the first diode and the second diode.

9. The power supply of claim 1 , wherein:

the at least one flip-flop comprises a D flip-flop coupled to receive an output from the VCO, the D flip-flop including a first output and a second output that is complementary to the first output;

a first one of the multiple logic gates is coupled to the first output of the D flip-flop to generate a first control signal having a fifty percent duty cycle; and

a second one of the multiple logic gates is coupled to the second output of the D flip-flop to generate a second control signal having a fifty percent duty cycle, wherein the second control signal is complementary to the first control signal.

10. The power supply of claim 9 , wherein:

the first one of the multiple logic gates is coupled to supply the first control signal to the first and second switches of the three-level LLC circuit; and

the second one of the multiple logic gates is coupled to supply the second control signal to the third switch.

11. The power supply of claim 1 , wherein the control circuit is coupled to:

turn on and turn off the first and second switches of the three-level LLC circuit at the same time; and

turn on the third switch while the first and second switches of the three-level LLC circuit are turned off.

12. The power supply of claim 1 , wherein:

the first and second switches of the three-level LLC circuit each comprise a voltage rating of less than or equal to 400V; and

the third switch comprises a voltage rating of less than or equal to 650V.

13. The power supply of claim 1 , wherein:

the first and second switches of the three-level LLC circuit each comprise a voltage rating of less than or equal to 650V; and

the third switch comprises a voltage rating of less than or equal to 1200V.

14. The power supply of claim 1 , wherein:

the first half-bridge and the second half-bridge of the three-level LLC circuit each comprise a single switch coupled with a single diode;

the three-level LLC circuit comprises a total of three switches coupled for active switching operation by the control circuit; and

the control circuit is configured to operate the three switches in a symmetrical half-bridge mode of operation.

15. A switch-mode power supply, comprising:

a pair of input terminals for receiving an alternating current (AC) or direct current (DC) voltage input from an input power source;

a pair of output terminals for supplying a direct current (DC) voltage output to a load;

a circuit ground;

a three-level LLC circuit coupled between the pair of input terminals and the pair of output terminals, the three-level LLC circuit arrangement including a first half-bridge having at least a first switch and a second half-bridge having at least a second switch, the first half-bridge coupled between the circuit ground and a first one of the pair of input terminals, and the second half-bridge coupled between the circuit ground and a second one of the pair of input terminals; and

a third switch coupled across a portion of the first half-bridge and a portion of the second half-bridge to short circuit said portions when the third switch is closed.

16. The power supply of claim 15 , further comprising a transformer and multiple secondary switches or diodes, wherein the transformer includes a primary winding and a secondary winding, the third switch is coupled with the primary winding, and the multiple secondary switches or diodes are coupled with the secondary winding.

17. The power supply of claim 16 , further comprising:

a first capacitor and a first inductor coupled between the primary winding and the first half- bridge; and

a second capacitor and a second inductor coupled between the primary winding the second half-bridge.

18. The power supply of claim 15 , further comprising:

a first capacitor coupled between the circuit ground and the first input terminal; and

a second capacitor coupled between the circuit ground and the second input terminal.

19. A switch-mode power supply, comprising:

a pair of input terminals for receiving an alternating current (AC) or direct current (DC) voltage input from an input power source;

a pair of output terminals for supplying a direct current (DC) voltage output to a load;

a transformer having a primary winding and a secondary winding;

at least two switches and two diodes coupled in a three-level LLC circuit between the pair of input terminals and the pair of output terminals;

a third switch coupled across the two diodes to short circuit the two diodes when the third switch is closed, the third switch coupled with the primary winding; and

a control circuit including a voltage-controlled oscillator (VCO), at least one flip-flop and multiple logic gates coupled to operate the three switches.

20. The power supply of claim 19 , wherein:

the at least one flip-flop comprises a D flip-flop coupled to receive an output from the VCO, the D flip-flop including a first output and a second output that is complementary to the first output;

a first one of the multiple logic gates is coupled to the first output of the D flip-flop to generate a first control signal having a fifty percent duty cycle; and

a second one of the multiple logic gates is coupled to the second output of the D flip-flop to generate a second control signal having a fifty percent duty cycle, wherein the second control signal is complementary to the first control signal.