Control circuit for a resonant circuit and the method thereof

A resonant circuit, comprising:

• a first switch, coupled between an input voltage terminal and a switching terminal, configured to receive a first control signal, wherein the first switch is turned on/off based on the first control signal;
• a second switch, coupled between the switching terminal and a primary ground terminal, configured to receive a second control signal, wherein the second switch is turned on/off based on the second control signal;
• and
• a control circuit, comprising:
• a resonant current detecting circuit configured to receive a resonant current, a first reference and a second reference, and to provide a detected current signal based on the resonant current, the first reference and the second reference;
• a current adjustment circuit configured to receive the detected current signal and a charging reference, and to provide an on-time control signal based on the detected current signal and the charging reference;
• and
• an on-time control circuit configured to receive the on-time control signal and an on-time initial value, and to provide an on-time signal to control the second switch of the resonant circuit based on the on-time control signal and the on-time initial value;
• and wherein the resonant current detecting circuit comprises:
• a first comparison circuit configured to receive the resonant current and the first reference, and to provide a first comparison signal based on the resonant current and the first reference;
• a second comparison circuit configured to receive the resonant current and the second reference, and to provide a second comparison signal based on the resonant current and the second reference;
• a first timing circuit configured to receive a timing start signal and the first comparison signal, and to provide a first timing signal;
• a second timing circuit configured to receive the timing start signal and the second comparison signal, and to provide a second timing signal;
• and
• a calculating circuit configured to receive the first reference, the second reference, the first timing signal and the second timing signal, and to provide the detected current signal based on the first reference, the second reference, the first timing signal and the second timing signal.

A control method for a resonant circuit having a transformer, a resonant capacitor coupled in series with a primary winding of the transformer, and a first switch and a second switch coupled in series between an input voltage terminal and a primary ground terminal, wherein the control method comprises:

• providing a first comparison signal based on a first reference and a resonant current;
• providing a second comparison signal based on a second reference and the resonant current;
• providing a first timing signal based on the first comparison signal and a timing start signal;
• providing a second timing signal based on the second comparison signal and the timing start signal;
• and
• providing a detected current signal based on the first reference and the second reference, the first timing signal and the second timing signal, wherein the detected current signal indicates a resonant current value at a start time represented by the timing start signal;
• providing an on-time control signal based on the detected current signal and a charging reference;
• and
• providing an on-time signal to control an on-time of the second switch of the resonant circuit based on the on-time control signal and an on-time initial value.