LLC resonant converter and control method thereof

A control method in use of an LLC converter, comprising:

• providing high-side and low-side switches connected in series between two input power lines via a first node, wherein connected to the first node is a resonant circuit with a primary winding of a transformer and a resonant capacitor both connected to a second node, and a voltage divider is connected to the second node to generate a feedback signal at a feedback node;
• generating first and second control signals to control the high-side and low-side switches respectively in response to the feedback signal and a compensation signal controlled by an output voltage of the LLC converter;
• comparing a first duty cycle of the first control signal with a second duty cycle of the second control signal to provide an accumulation signal;
• and
• providing an adjustment current in response to the accumulation signal to adjust an average of the feedback signal.

A common-voltage modifier in use of an LLC converter, comprising:

• a duty-cycle comparator for comparing a first duty cycle of a high-side switch and a second duty cycle of a low-side switch to provide an accumulated signal, wherein the high-side and low-side switches connected in series between two input power lines via a first node;
• and
• a voltage-controllable current source for providing, in response to the accumulated signal, an adjustment current to shift an average of a feedback signal;
• wherein the high-side and low-side switches are controlled in response to the feedback signal and a compensation signal to provide a square-wave voltage to a resonant tank, a voltage divider is connected between the resonant tank and one of the input power lines to provide the feedback signal, and the compensation signal is controlled by an output voltage of the LLC converter.