Controller for resonant converter

1 . A controller for a resonant converter, the resonant converter comprising:

a first switch;

a resonant tank coupled to the first switch at a switching node; and

a first capacitor;

wherein the controller is configured to:

operate in a first mode by:

providing a plurality of first periodic control pulses to drive the switching of the first switch at a first switching frequency;

operate in a second mode by:

providing the plurality of first periodic control pulses to drive the switching of the first switch at a second switching frequency, the second switching frequency being less than the first switching frequency, or stopping providing the first periodic control pulses; and

providing one or more first charging pulses, each of the one or more first charging pulses driving the switching of the first switch to charge the first capacitor.

2 . The controller of claim 1 , wherein the first charging pulses comprises a plurality of periodic first charging pulses.

3 . The controller of claim 2 , wherein a first pulse width and/or a first charging pulse frequency of the periodic first charging pulses is determined based on a capacitance of the first capacitor and/or a resistance of a first discharge resistor.

4 . The controller of claim 1 , further comprising:

a first gate driver configured to provide the one or more first charge pulses to the first switch; and

a first detector configured to:

detect a first voltage across the first capacitor;

determine whether the first voltage is below a first threshold value; and

provide a first control signal to the first gate driver when the first voltage is below the first threshold value;

wherein the first gate driver is configured to provide the one or more first charge pulses to the first switch to charge the first capacitor in response to receiving the first control signal from the first detector.

5 . The controller of claim 4 , further comprising an isolation circuit for providing electrical isolation, the first control signal being provided to the first gate driver via the isolation circuit.

6 . The controller of claim 1 , wherein the resonant converter comprises:

a second switch coupled to the switching node; and

a second capacitor.

7 . The controller of claim 6 , wherein the controller is configured to:

operate in the first mode by:

providing a plurality of periodic second control pulses to drive the switching of the second switch at a third switching frequency;

operate in a second mode by:

providing the plurality of periodic second control pulses to drive the switching of the second switch at a fourth switching frequency, the fourth switching frequency being less than the third switching frequency, or stopping providing the second periodic control pulses; and

providing one or more second charging pulses, each of the one or more second charging pulses driving the switching of the second switch to charge the second capacitor.

8 . The controller of claim 7 , wherein the controller is configured to drive the switching of the first and second switches such that both the first and second switches are not simultaneously on an on state.

9 . The controller of claim 7 , wherein:

the first charging pulses comprises a plurality of periodic first charging pulses; and/or

the second charging pulses comprises a plurality of periodic second charging pulses.

10 . The controller of claim 9 , wherein:

a first pulse width and/or a first charging pulse frequency of the periodic first charging pulses is determined based on a capacitance of the first capacitor and/or a resistance of a first discharge resistor; and/or

a second pulse width and/or a second charging pulse frequency of the periodic second charging pulses is determined based on a capacitance of the second capacitor and/or a resistance of a second discharge resistor or the load current discharged from the second capacitor or the load current to the second capacitor.

11 . The controller of claim 7 , comprising:

a first gate driver configured to provide the one or more first charge pulses to the first switch;

a second gate driver configured to provide the one or more second charge pulses to the second switch;

a first detector configured to:

detect a first voltage across the first capacitor; and

determine whether the first voltage is below a first threshold value; and

provide a first control signal to the first gate driver when the first voltage is below the first threshold value; and

a second detector configured to:

detect a second voltage across the second capacitor;

determine whether the second voltage is below a second threshold value; and

provide a second control signal to the second gate driver when the second voltage is below the second threshold value;

wherein:

the first gate driver is configured to provide the one or more first charge pulses to the first switch to charge the first capacitor in response to receiving the first control signal from the first detector; and

the second gate driver is configured to provide the one or more second charge pulses to the second switch to charge the second capacitor in response to receiving the second control signal from the second detector.

12 . The controller of claim 11 , further comprising:

a first isolation circuit for providing electrical isolation, the first control signal being provided to the first gate driver via the first isolation circuit; and/or

a second isolation circuit for providing electrical isolation, the second control signal being provided to the second gate driver via the second isolation circuit.

13 . The controller of claim 11 , wherein:

the first switch is a high side switch;

the second switch is a low side switch;

the first capacitor is a resonant capacitor, the resonant tank comprising the first capacitor; and

the second capacitor is a bootstrap capacitor.

14 . The controller of claim 13 , wherein:

the resonant converter comprises a first resistor configured to be coupled to a supply voltage, and a first diode coupled to the first resistor and the second capacitor;

the resonant tank comprises a first inductor coupled to the switching node and the first capacitor; and

the second capacitor is coupled to the switching node.

15 . The controller of claim 14 , wherein:

the first detector is configured to detect a first voltage across the first capacitor by sensing a switching node voltage at the switching node or at a first capacitor node; and

the second detector is configured to detect a second voltage across the second capacitor by sensing the switching node voltage and a bootstrap voltage at a bootstrap node between the first diode and the second capacitor.

16 . The controller of claim 1 , wherein the resonant converter is an asymmetrical half-bridge resonant converter.

17 . The controller of claim 1 , wherein the second mode is a low power mode in which the resonant converter operates to provide a reduced load current when compared to the first mode.

18 . The controller of claim 1 , wherein the controller is configured to provide pulse frequency modulation (PFM) during the first and/or second mode.

19 . An apparatus comprising:

a resonant converter comprising:

a first switch;

a resonant tank coupled to the first switch at a switching node; and

a first capacitor; and

a controller configured to:

operate in a first mode by:

providing a plurality of first periodic control pulses to drive the switching of the first switch at a first switching frequency;

operate in a second mode by:

providing the plurality of first periodic control pulses to drive the switching of the first switch at a second switching frequency, the second switching frequency being less than the first switching frequency, or stopping providing the first periodic control pulses; and

providing one or more first charging pulses, each of the one or more first charging pulses driving the switching of the first switch to charge the first capacitor.

20 . A method of controlling a resonant converter, the resonant converter comprising:

a first switch;

a resonant tank coupled to the first switch at a switching node; and

a first capacitor;

wherein the method comprises:

operating a controller in a first mode in which the controller:

provides a plurality of first periodic control pulses to drive the switching of the first switch at a first switching frequency;

operating in the controller in a second mode in which the controller:

provides the plurality of first periodic control pulses to drive the switching of the first switch at a second switching frequency, the second switching frequency being less than the first switching frequency, or stops providing the first periodic control pulses; and

provides one or more first charging pulses, each of the one or more first charging pulses driving the switching of the first switch to charge the first capacitor.