Resonant converter and method of operating the same

1 . A method of operating a resonant converter, the resonant converter comprising a transformer and a primary-side circuit; the primary-side circuit comprising a resonant circuit, and the resonant circuit being coupled to a primary-side winding of the transformer to form a resonant module, the method comprising steps of:

controlling the primary-side circuit to convert a DC voltage so as to control the resonant converter converting the DC voltage into an output voltage to generate a winding voltage at two ends of the resonant module,

detecting an output current of the resonant converter, and adjusting a duty cycle of the winding voltage with a variation when determining that the output current is in a current interval between a predetermined current and a rated current, so that the duty cycle does not remain at a predetermined value,

adjusting the duty cycle to control an operation frequency of the resonant convert to vary within a frequency range, and the frequency range is positively related to the variation, and

setting a threshold value of the variation to decrease according to the increase of the output current, and the frequency range is expanded according to the decrease of the threshold value.

2 . The method of operating the resonant converter as claimed in claim 1 , further comprising a step of:

fixing the duty cycle to the predetermined value when the output current is less than the predetermined current or is greater than the rated current.

3 . The method of operating the resonant converter as claimed in claim 1 , further comprising a step of:

setting a threshold value of the variation to a fixed value, and the frequency range is in a specific range corresponding to the threshold value.

4 . The method of operating the resonant converter as claimed in claim 1 , wherein the primary-side circuit comprises a first bridge arm and a second bridge arm connected in parallel; the first bridge arm comprises a first switch and a second switch, and the second bridge arm comprises a third switch and a fourth switch, the method further comprises steps of:

providing a first control signal to control the first switch, providing a second control signal to control the second switch, providing a third control signal to control the third switch, and providing a fourth control signal to control the fourth switch, and

controlling a phase shift of phase variation of the first control signal and the fourth control signal to adjust the variation when the output current is in the current interval; or controlling the phase shift of phase variation of the second control signal and the third control signal to adjust the variation when the output current is in the current interval.

5 . The method of operating the resonant converter as claimed in claim 4 , further comprising steps of:

comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal,

generating a pulse-width modulation value and a variation value corresponding to the variation according to the error signal,

modulating the first control signal, the second control signal, the third control signal, and the fourth control signal according to the pulse-width modulation value, and

adjusting the phase shift according to the variation value.

6 . The method of operating the resonant converter as claimed in claim 1 , wherein the primary-side circuit comprises a first bridge arm, and the first bridge arm comprises a first switch and a second switch, the method further comprises steps of:

providing a first control signal to control the first switch and providing a second control signal to control the second switch, and

adjusting a dead time between the first control signal and the second control signal to adjust the variation when the output current is in the current interval.

7 . The method of operating the resonant converter as claimed in claim 6 , further comprising steps of:

comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal,

generating a pulse-width modulation value and a variation value corresponding to the variation according to the error signal,

modulating the first control signal and the second control signal according to the pulse-width modulation value, and

adjusting the dead time according to the variation value.

8 . A method of operating a resonant converter, the resonant converter comprising a transformer and a primary-side circuit, and the primary-side circuit comprising a resonant circuit and a first bridge arm; the resonant circuit being coupled to a primary-side winding of the transformer to form a resonant module, and the first bridge arm comprises a first switch and a second switch, the method comprising steps of:

controlling the primary-side circuit to convert a DC voltage so as to control the resonant converter converting the DC voltage into an output voltage to generate a winding voltage at two ends of the resonant module,

detecting an output current of the resonant converter, and adjusting a duty cycle of the winding voltage with a variation when determining that the output current is in a current interval between a predetermined current and a rated current, so that the duty cycle does not remain at a predetermined value,

adjusting the duty cycle to control an operation frequency of the resonant convert to vary within a frequency range, and the frequency range is positively related to the variation,

providing a first control signal to control the first switch and providing a second control signal to control the second switch, and

adjusting a dead time between the first control signal and the second control signal to adjust the variation when the output current is in the current interval.

9 . The method of operating the resonant converter as claimed in claim 8 , further comprising a step of:

fixing the duty cycle to the predetermined value when the output current is less than the predetermined current or is greater than the rated current.

10 . The method of operating the resonant converter as claimed in claim 8 , further comprising a step of:

setting a threshold value of the variation to a fixed value, and the frequency range is in a specific range corresponding to the threshold value.

11 . The method of operating the resonant converter as claimed in claim 8 , wherein the primary-side circuit comprises a first bridge arm and a second bridge arm connected in parallel; the first bridge arm comprises a first switch and a second switch, and the second bridge arm comprises a third switch and a fourth switch, the method further comprises steps of:

providing a first control signal to control the first switch, providing a second control signal to control the second switch, providing a third control signal to control the third switch, and providing a fourth control signal to control the fourth switch, and

controlling a phase shift of phase variation of the first control signal and the fourth control signal to adjust the variation when the output current is in the current interval; or controlling the phase shift of phase variation of the second control signal and the third control signal to adjust the variation when the output current is in the current interval.

12 . The method of operating the resonant converter as claimed in claim 11 , further comprising steps of:

comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal,

generating a pulse-width modulation value and a variation value corresponding to the variation according to the error signal,

modulating the first control signal, the second control signal, the third control signal, and the fourth control signal according to the pulse-width modulation value, and

adjusting the phase shift according to the variation value.

13 . The method of operating the resonant converter as claimed in claim 8 , further comprising steps of:

comparing a feedback signal corresponding to the output voltage with a reference voltage to provide an error signal,

generating a pulse-width modulation value and a variation value corresponding to the variation according to the error signal,

modulating the first control signal and the second control signal according to the pulse-width modulation value, and

adjusting the dead time according to the variation value.