Resonant converter using variably delayed output switching

1. A resonant converter including:

a resonant tank;

a switching circuit that connects the resonant tank to a power supply according to a first switching sequence;

a synchronous rectifier circuit that supplies power to an output; wherein the rectifier circuit is switched according to a second switching sequence; and

a phase delay module arranged to delay the second switching sequence with respect to the first switching sequence by a variable phase delay to achieve a desired power output, said phase delay module configured to use feedback from the output to develop an error signal based on a difference between a nominal value of a voltage at the output and an actual value of the voltage at the output, said error signal having a characteristic that varies in response to a first change in the actual value of the voltage at the output to thereby cause a change in the variable phase delay and a corresponding second change in the actual value of the voltage at the output that results from the change in the variable phase delay;

wherein the second switching sequence is a phase delayed version of the first switching sequence and wherein a duty cycle of the first switching sequence is equivalent to a duty cycle of the second switching sequence.

2. The resonant converter of claim 1 further including a transformer arranged between the power supply and the output.

3. The resonant converter of claim 2 , wherein the transformer is one of an isolation transformer and an auto transformer.

4. The resonant converter of claim 2 , wherein the resonant tank includes an inductor and a capacitor in series on a primary side of the transformer.

5. The resonant converter of claim 4 , wherein the inductor in series with the capacitor is a first inductor and the resonant tank is independent of a second inductor in parallel with the primary side of the transformer.

6. The resonant converter of claim 2 , wherein the resonant tank includes an inductor and a capacitor in series on a secondary side of the transformer.

7. The resonant converter of claim 2 , wherein the resonant tank includes an inductor on a primary side of the transformer and a capacitor in series on a secondary side of the transformer.

8. The resonant converter of claim 2 , wherein the resonant tank includes an inductor on a secondary side of the transformer and a capacitor in series on a primary side of the transformer.

9. The resonant converter of claim 1 , wherein the resonant tank includes an inductor and capacitor in series, and the power supply is not isolated from the output.

10. The resonant converter of claim 1 , wherein the switching circuit is arranged as a half bridge drive circuit.

11. The resonant converter of claim 1 , wherein the resonant tank includes an inductor and a capacitor in series.

12. The resonant converter of claim 1 , wherein the resonant tank includes a single inductor.

13. The resonant converter of claim 1 , wherein the switching circuit and synchronous rectifier circuit employ Zero Voltage Transition (ZVT) switching.

14. The resonant converter of claim 1 further arranged to adjust the alignment of the first and second switching sequences dependent on the desired output.

15. The resonant converter of claim 1 , wherein the first switching sequence is at a fixed operating frequency.

16. The resonant converter of claim 15 , wherein the first switching sequence is varied to spread the frequency spectrum.

17. The resonant converter of claim 1 , wherein the first switching sequence is at a variable operating frequency.

18. The resonant converter of claim 1 , wherein the switching circuit further includes two or more switching devices arranged to charge and discharge the resonant tank.

19. The resonant converter of claim 1 , wherein a first switching device is connected between a first node of an inductor forming part of the resonant tank and a first DC power supply node, and a second switching device is connected between the first node of the inductor and a second DC power supply node.

20. The resonant converter of claim 1 ,

wherein the switching circuit comprises:

a first half bridge drive circuit; and

a driver circuit that drives the first half bridge drive circuit responsive to a first oscillator signal,

wherein the phase delay module is configured to generate, from the first oscillator signal, a second oscillator signal which is a delayed version of the first oscillator signal, and

wherein the synchronous rectifier circuit is switched according to the second oscillator signal.

21. The resonant converter of claim 20 , wherein the first oscillator signal and the second oscillator signal are fixed frequency signals.

22. A resonant converter including:

a resonant tank;

a switching circuit that connects the resonant tank to a power supply according to a first switching sequence having a first duty cycle;

a synchronous rectifier circuit that supplies power to an output and is switched according to a second switching sequence; and

a phase delay module arranged to delay the second switching sequence with respect to the first switching sequence by a variable phase delay to achieve a desired power output, said phase delay module configured to use feedback from the output to develop an error signal based on a difference between a nominal value of a voltage at the output and an actual value of the voltage at the output, said error signal having a characteristic that varies in response to a first change in the actual value of the voltage at the output to thereby cause a change in the variable phase delay and a corresponding second change in the actual value of the voltage at the output that results from the change in the variable phase delay.

23. The resonant converter of claim 22 , wherein a duty cycle of the first switching sequence is equivalent to a duty cycle of the second switching sequence for all values of the variable phase delay.