Resonant power converters and control methods for wide input and output voltage ranges

1. A resonant converter, comprising:

first and second primary side input terminals;

a primary side resonant circuit including two or more primary side switches;

a transformer having primary and secondary windings;

a secondary side rectifier circuit;

output points of the secondary side rectifier circuit connected to first and second secondary side output terminals;

an output capacitor connected across the first and second output terminals;

a secondary side blocking capacitor wherein a first terminal of the blocking capacitor is connected to the transformer secondary winding and a second terminal of the blocking capacitor is connected to a second input terminal of the rectifier circuit;

a secondary side control switch wherein a first terminal of the secondary side control switch is connected to the second terminal of the blocking capacitor and a second terminal of the secondary side control switch is connected to a second output point of the rectifier circuit; and

at least one controller that controls a switching frequency of the two or more primary side switches according to a lower switching frequency when the secondary side control switch is off, and according to a higher switching frequency when the secondary side control switch is on, and controls the secondary side control switch according to a first selected mode so that when the secondary side control switch is off, the output voltage of the resonant converter is Vo, and according to a second selected mode so that when the secondary side control switch is on, the output voltage of the resonant converter is 2Vo.

2. The resonant converter of claim 1 , wherein the at least one controller controls a duty cycle of the secondary side control switch during a transition from off to on, wherein the duty cycle gradually increases from 0 to 1 during switching cycles over a first selected duration; and

wherein the at least one controller controls the duty cycle of the secondary side control switch during a transition from on to off, wherein the duty cycle gradually decreases from 1 to 0 during switching cycles over a second selected duration.

3. The resonant converter of claim 2 , wherein the first selected duration corresponds to a duration in which the switching frequency of the two or more primary side switches is increasing; and

wherein the second selected duration corresponds to a duration in which the switching frequency of the two or more primary side switches is decreasing.

4. The resonant converter of claim 1 , wherein the at least one controller controls a duty cycle of the secondary side control switch within each switching cycle;

wherein the output voltage of the resonant converter is determined by the duty cycle of the secondary side control switch within each switching cycle;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

5. The resonant converter of claim 1 , wherein the at least one controller controls the secondary side control switch by:

turning on the secondary side control switch during alternating negative halves of the transformer secondary current cycle; and

otherwise turning off the secondary side control switch;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

6. The resonant converter of claim 1 , wherein the at least one controller controls the secondary side control switch by:

turning on the secondary side control switch during a selected number of consecutive negative halves of a transformer secondary current cycle;

turning off the secondary side control switch during a selected number of consecutive negative halves of the transformer secondary current cycle; and

otherwise turning off the secondary side control switch;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

7. The resonant converter of claim 1 , further comprising a primary side control switch;

wherein a reactive element of the primary side resonant circuit comprises first and second reactive elements;

wherein the primary side control switch is connected to the first and second reactive elements;

wherein the at least one controller controls the primary side control switch according to a third selected mode;

wherein the third selected mode changes a total reactance of the first and second reactive elements;

wherein a voltage at the first and second output terminals is variable between K*Vo and 2Vo, where K is a number between 0 and 1, according to the first, second, and third selected modes.

8. The resonant converter of claim 7 , wherein the at least one controller controls the primary side control switch according to a mode wherein the control switch is alternately off and on during consecutive switching cycles of the two or more primary side switches;

wherein the voltage at the first and second output terminals is between K*Vo and Vo, where K is a number between 0 and 1.

9. A method for implementing a resonant converter, wherein the resonant converter comprises:

first and second primary side input terminals;

a primary side resonant circuit including two or more primary side switches;

a transformer having primary and secondary windings;

a secondary side rectifier circuit;

output points of the secondary side rectifier circuit connected to first and second secondary side output terminals;

an output capacitor connected across the first and second output terminals;

a secondary side blocking capacitor wherein a first terminal of the blocking capacitor is connected to the transformer secondary winding and a second terminal of the blocking capacitor is connected to a second input terminal of the rectifier circuit; and

a secondary side control switch wherein a first terminal of the secondary side control switch is connected to the second terminal of the blocking capacitor and a second terminal of the secondary side control switch is connected to a second output point of the rectifier circuit;

the method comprising controlling a switching frequency of the two or more primary side switches according to a lower switching frequency when the secondary side control switch is off, and according to a higher switching frequency when the secondary side control switch is on, and controls the secondary side control switch according to a first selected mode so that when the secondary side control switch is off, the output voltage of the resonant converter is Vo, and according to a second selected mode so that when the secondary side control switch is on, the output voltage of the resonant converter is 2Vo.

10. The method of claim 9 , comprising controlling a duty cycle of the secondary side control switch during a transition from off to on, wherein the duty cycle gradually increases from 0 to 1 during switching cycles over a first selected duration; and

controlling the duty cycle of the secondary side control switch during a transition from on to off, wherein the duty cycle gradually decreases from 1 to 0 during switching cycles over a second selected duration.

11. The method of claim 10 , wherein the first selected duration corresponds to a duration in which a switching frequency of the resonant converter is increasing; and

wherein the second selected duration corresponds to a duration in which the switching frequency of the resonant converter is decreasing.

12. The method of claim 9 , comprising controlling a duty cycle of the secondary side control switch within each switching cycle;

wherein the output voltage of the resonant converter is determined by the duty cycle of the secondary side control switch within each switching cycle;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

13. The method of claim 9 , comprising controlling the secondary side control switch by:

turning on the secondary side control switch during alternating negative halves of the transformer secondary current cycle; and

otherwise turning off the secondary side control switch;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

14. The method of claim 9 , comprising controlling the secondary side control switch by:

turning on the secondary side control switch during a selected number of consecutive negative halves of a transformer secondary current cycle;

turning off the secondary side control switch during a selected number of consecutive negative halves of the transformer secondary current cycle; and

otherwise turning off the secondary side control switch;

wherein the output voltage of the resonant converter is variable and is regulated at a value from Vo to 2Vo.

15. The method of claim 9 , wherein the resonant converter further comprises a primary side control switch;

wherein a reactive element of the primary side resonant circuit comprises first and second reactive elements;

wherein the primary side control switch is connected to the first and second reactive elements;

the method comprising controlling the primary side control switch according to a third selected mode;

wherein the third selected mode changes a total reactance of the first and second reactive elements;

wherein a voltage at the first and second output terminals is variable between K*Vo and 2Vo, where K is a number between 0 and 1, according to the first, second, and third selected modes.

16. The method of claim 15 , comprising controlling the primary side control switch according to a mode wherein the control switch is alternately off and on during consecutive switching cycles of the two or more primary side switches;

wherein the voltage at the first and second output terminals is between K*Vo and Vo, where K is a number between 0 and 1.