Controller for a resonant converter and a method of operating a resonant converter

A method of operating a resonant converter, wherein the resonant converter is for supplying electrical energy from a supply source to a load, the resonant converter comprising:

• a first switch and a second switch connected in series with each other between the supply source and a reference terminal, wherein the resonant converter has a high-side switch half cycle when the first switch is closed and the second switch is open, and wherein the resonant converter has a low-side switch half cycle when the first switch is open and the second switch is closed;
• and
• a resonant tank that is electrically connected to the first and second switches, wherein the resonant tank comprises a resonant capacitor;
• wherein the method comprises:
• receiving a measured current signal that represents a current flowing in the resonant tank;
• receiving a measured voltage signal that represents a voltage at a predetermined point in the resonant tank;
• receiving a power setting signal, which defines a requested power level for the load;
• if the measured current signal is greater than an upper-low-load-current-threshold, then setting an upper-voltage-threshold-value based on the measured current signal;
• if the measured current signal is not greater than the upper-low-load-current-threshold, then setting the upper-voltage-threshold-value based on the power setting signal but independent of the measured current signal;
• if the measured current signal is less than a lower-low-load-current-threshold, then setting a lower-voltage-threshold-value based on the measured current signal;
• if the measured current signal is not less than the lower-low-load-current-threshold, then setting the lower-voltage-threshold-value based on the power setting signal but independent of the measured current signal;
• in response to the measured voltage signal exceeding the upper-voltage-threshold-value, opening the first switch and closing the second switch;
• and
• in response to the measured voltage signal dropping below the lower-voltage-threshold-value, opening the second switch and closing the first switch.