Efficient LLC resonant converter having variable frequency control and fixed frequency phase-shift PWM

1. A method of operating a LLC resonant converter circuit, the LLC resonant converter circuit including a resonant filter, the LLC resonant converter circuit being operated at an operational frequency and having an inverter coupled to the resonant filter that produces a first waveform and a second waveform, the first waveform having a phase shift with respect to the second waveform, the method comprising:

receiving an output voltage of the LLC resonant converter circuit;

analyzing the received output voltage to determine whether the received output voltage is within an acceptable operational range;

when the output voltage is not within the acceptable operational range and the operational frequency is below a maximum predetermined frequency, adjusting the operational frequency of the LLC resonant converter circuit, the adjusting of the operational frequency being effective to change the output voltage to a value that is within the acceptable operational range such that efficient operation of a plurality of inverter transistors is maintained by operating at a frequency above a boundary condition and within a gain-versus-frequency area bounded by a plurality q-value curves between a minimum gain and a maximum gain, wherein the plurality of q-value curves each have distinct peak q-values relative to one another;

when the output voltage is not within the acceptable operational range and the operational frequency is above the maximum predetermined frequency, adjusting a phase shift in the LLC resonant converter circuit to adjust the output voltage to a value that is within the acceptable operational range.

2. The method of claim 1 , wherein the first waveform and the second waveform are produced by the actuation of pairs of transistors.

3. The method of claim 1 wherein the overlap between the two waveforms is approximately 180 degrees.

4. The method of claim 1 wherein the overlap between the two waveforms is shifted from approximately 180 degrees to a value substantially below 180 degrees.

5. The method of claim 1 , wherein the output voltage is desired to be approximately 12 volts.

6. The method of claim 1 , wherein the output voltage is used to power an accessory of a vehicle.

7. The method of claim 1 , wherein the voltage is transformed down to a voltage of approximately 12 volts.

8. An LLC resonant converter circuit, comprising:

an inverter circuit, the inverter circuit producing a first waveform and a second waveform that are summed into a third waveform;

a resonant filter coupled to the inverter circuit, the resonant filter receiving the third waveform and converting the third waveform into a sinusoidal waveform;

a transformer isolator that converts the sinusoidal waveform from a first voltage to a second voltage;

a controller coupled to the inverter circuit;

a rectifier and output circuit coupled to the isolation transformer;

wherein the inverter is operated at an operational frequency by the controller and wherein the controller operates such that the first waveform has a phase shift with respect to the second waveform;

wherein the controller is coupled to the output circuit, the controller configured to, based upon a maximum frequency of operation, when the output voltage needs to be adjusted and the operational frequency is below the maximum frequency, adjust the operational frequency of operation of the inverter circuit to adjust the output voltage to a desired value such that efficient operation of a plurality of inverter transistors is maintained by operating at a frequency above a boundary condition and within a gain-versus-frequency area bounded by a plurality q-value curves between a minimum gain and a maximum gain, wherein the plurality of q-value curves each have distinct peak q-values relative to one another, and when the output voltage needs to be adjusted and the operational frequency is above the maximum frequency, adjust the phase shift of the first waveform and the second waveform to adjust the output voltage to a desired value.

9. The circuit of claim 8 , wherein the first waveform and the second waveform are produced by the actuation of pairs of transistors.

10. The circuit of claim 8 wherein the overlap between the two waveforms is approximately 180 degrees.

11. The circuit of claim 8 wherein the overlap between the two waveforms is shifted from approximately 180 degrees to a value substantially below 180 degrees.

12. The circuit of claim 8 , wherein the output voltage is desired to be approximately 12 volts.

13. The circuit of claim 8 , wherein the output voltage is used to power an accessory of a vehicle.