DC/DC resonant converters and power factor correction using resonant converters, and corresponding control methods
Various improvements are provided to resonant DC/DC and AC/DC converter circuit. The improvements are of particular interest for LLC circuits. Some examples relate to self-oscillating circuit and others relate to converter circuits with frequency control, for example for power factor correction, driven by an oscillator.
1. A converter, comprising:
a half bridge inverter comprising a first switch and a second switch, wherein a first output is defined from a node between the switches;
an LLC circuit comprising a second output for supplying an output voltage and an output current, and being coupled to the first output, wherein an electrical feedback parameter is provided by the LLC circuit;
a control circuit for generating a gate drive signal for controlling the switching of the first switch and the second switch in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on one switch and turns off the other switch and a low gate drive signal turns off the one switch and turns on the other switch,
wherein the control circuit comprises:
an outer control loop for setting a threshold level proportionally to at least the converter output voltage or current;
an inner control loop for reducing an effect of false or missing triggers in the converter, wherein the inner control loop includes an oscillator for generating the gate drive signal and a comparator for controlling a frequency of the oscillator based on an average value of a comparison between the threshold level and the electrical feedback parameter; and
wherein the threshold level is an input current threshold level, and the inner control loop comprises an integrator arranged to integrate an error in a desired input current, wherein the oscillator is controlled in dependence on the integrated error and the electrical feedback parameter.
2. The converter as claimed in claim 1 , wherein the electrical feedback parameter corresponds to a voltage across a capacitor of the LLC circuit.
3. The converter as claimed in claim 1 , wherein the oscillator comprises circuitry for implementing duty cycle modification in dependence on the output load.
4. An AC/DC PFC converter, comprising:
an AC input;
a rectifier; and
the converter as claimed in claim 1 , wherein the outer control loop is for setting the threshold level taking into account the rectified input voltage and an input current.
5. An LED driver, comprising:
the converter as claimed in claim 1 , and an isolation transformer at the output of the self-oscillating LLC circuit, wherein the secondary side of the isolation transformer is for driving an LED load.
6. A converter, comprising:
a half bridge inverter comprising a first switch and a second switch, wherein a first output is defined from a node between the switches;
an LLC circuit comprising a second output for supplying an output voltage and an output current, and being coupled to the first output, wherein an electrical feedback parameter is provided by the LLC circuit;
a control circuit for generating a gate drive signal for controlling the switching of the first switch and the second switch in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on one switch and turns off the other switch and a low gate drive signal turns off the one switch and turns on the other switch,
wherein the control circuit comprises:
an outer control loop for setting a threshold level proportionally to at least the converter output voltage or current;
an inner control loop for reducing an effect of false or missing triggers in the converter, wherein the inner control loop includes an oscillator for generating the gate drive signal and a comparator for controlling a frequency of the oscillator based on an average value of a comparison between the threshold level and the electrical feedback parameter, and
wherein the threshold level is a threshold level for the electrical feedback parameter, and the inner control loop comprises a phase detector for detecting a phase difference between a signal having timing dependent on the threshold level and the electrical feedback parameter and an integrator for integrating a phase difference, wherein the oscillator is controlled in dependence on the integrated phase difference.
7. A conversion method, comprising:
operating a half bridge inverter comprising a high side switch and a low side switch using a gate drive signal and providing an output from a node between the switches, wherein a high gate drive signal turns on one switch and turns off the other switch and a low gate drive signal turns off the one switch and turns on the other switch;
providing an electrical feedback parameter from an LLC circuit coupled to the output; and
controlling the switching of the high side and low side switches in dependence on the electrical feedback parameter, by:
setting a threshold level proportionally to the converter output voltage or current and a rectified input voltage in an outer control loop;
reducing, via an inner control loop, an effect of false or missing triggers in the converter, wherein the inner control loop comprises an oscillator for generating the gate drive signal, setting an oscillator frequency based on an average value of a comparison between the threshold level and the electrical feedback parameter; and
wherein the threshold level is an input current threshold level, and the inner control loop comprises an integrator for integrating an input current error, wherein the method comprises controlling the oscillator in dependence on the integrated current error and the electrical feedback parameter.
8. The method as claimed in claim 7 , wherein the electrical feedback parameter comprises a voltage across a capacitor of the LLC circuit.
9. The method as claimed in claim 7 , comprising implementing duty cycle modification in dependence on the output load.
10. A conversion method, comprising:
operating a half bridge inverter comprising a high side switch and a low side switch using a gate drive signal and providing an output from a node between the switches, wherein a high gate drive signal turns on one switch and turns off the other switch and a low gate drive signal turns off the one switch and turns on the other switch;
providing an electrical feedback parameter from an LLC circuit coupled to the output; and
controlling the switching of the high side and low side switches in dependence on the electrical feedback parameter, by:
setting a threshold level proportionally to the converter output voltage or current and a rectified input voltage in an outer control loop;
reducing, via an inner control loop, an effect of false or missing triggers in the converter, wherein the inner control loop comprises an oscillator for generating the gate drive signal, setting an oscillator frequency based on an average value of a comparison between the threshold level and the electrical feedback parameter; and
wherein the threshold level is a threshold level for the electrical feedback parameter, and the method comprises, in the inner control loop, detecting a phase difference between the threshold level and the electrical feedback parameter.
11. The method as claimed in claim 10 , comprising integrating a phase error, and controlling the oscillator in dependence on the integrated phase error.