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. An AC/DC PFC converter, comprising:
an AC input;
a rectifier;
a half bridge inverter comprising a first switch and a second switch, wherein an output is defined from a node between the first and second switches;
a self-oscillating LLC circuit coupled to the output, the self-oscillating LLC circuit being arranged to provide an electrical feedback parameter; and
a control circuit for generating a gate drive signal for controlling switching of the first and second switches in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch,
wherein the control circuit is for determining a first time duration corresponding to an on-time of the first switch and for determining a second time duration corresponding to an on-time of the second switch, the duty cycle of the second switch having a defined value,
and wherein the control circuit further comprises an integrator for:
integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value defining the first time duration;
subsequently integrating a second constant value of opposite sign to the first constant value defining the second time duration;
wherein the first and second constant values are derived from the gate drive signal;
wherein the integrator has a reference input set to a fixed voltage within a range of the gate drive signal; and
wherein the integrator has the reference input set to a mid-point of the gate drive signal.
2. The AC/DC PFC converter as claimed in claim 1 , comprising a transformer between the self-oscillating LLC circuit and an output load.
3. An apparatus comprising
the converter as claimed in claim 1 ; and
the output load.
4. The apparatus as claimed in claim 3 where the output load is an LED arrangement of one or more LEDs.
5. An AC/DC PFC converter, comprising:
an AC input;
a rectifier;
a half bridge inverter comprising a first switch and a second switch, wherein an output is defined from a node between the first and second switches;
a self-oscillating LLC circuit coupled to the output, the LLC circuit being arranged to provide an electrical feedback parameter; and
a control circuit for generating a gate drive signal for controlling the switching of the first and second switches in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch,
wherein the control circuit is for determining a first time duration corresponding to an on-time of the first switch and for determining a second time duration corresponding to an on-time of the second switch, the duty cycle of the second switch having a defined value,
and wherein the control circuit further comprises an integrator for:
integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value defining the first time duration;
subsequently integrating a second constant value of opposite sign to the first constant value defining the second time duration; and an RC output filter at an output of the integrator.
6. The AC/DC PFC converter as claimed in claim 5 , further comprising a shorting transistor at an output of the RC output filter, which is turned on when the integrator output is a falling slope and is turned off when the integrator output is a rising slope.
7. An AC/DC PFC converter, comprising:
an AC input;
a rectifier;
a half bridge inverter comprising a first switch and a second switch, wherein an output is defined from a node between the first and second switches;
a self-oscillating LLC circuit coupled to the output, the self-oscillating LLC circuit being arranged to provide an electrical feedback parameter; and
a control circuit for generating a gate drive signal for controlling the switching of the first and second switches in dependence on the electrical feedback parameter, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch,
wherein the control circuit is for determining a first time duration corresponding to an on-time of the first switch and for determining a second time duration corresponding to an on-time of the second switch, the duty cycle of the second switch having a defined value,
and wherein the control circuit further comprises an integrator for:
integrating a first constant value until the control circuit detects that the electrical feedback parameter reaches a threshold value defining the first time duration;
subsequently integrating a second constant value of opposite sign to the first constant value defining the second time duration; and wherein the electrical feedback parameter comprises a voltage across a capacitor of the LLC circuit.
8. An AC/DC PFC conversion method, comprising:
rectifying an AC input;
operating a half bridge inverter comprising a first switch and a second switch using a gate drive signal and providing an output from a node between the switches, wherein a high gate drive signal turns on the first switch and turns off the second switch and a low gate drive signal turns off the first switch and turns on the second switch;
providing an electrical feedback parameter from a self-oscillating LLC circuit coupled to the output, wherein the electrical feedback parameter is provided by the self-oscillating LLC circuit;
controlling switching of the first and second switches by:
determining a first time duration corresponding to an on-time of the first switch and determining a second time duration corresponding to an on-time of the second switch, and
integrating a first constant value until the electrical feedback parameter reaches a threshold value defining the first time duration; and
subsequently integrating a second constant value of opposite sign to the first constant value defining the second time duration; and
wherein the constant values are derived from the gate drive signal, and the step of integrating includes setting a reference input to a fixed voltage within the range of the gate drive signal and the reference input set to the mid-point of the gate drive signal.
9. An LED driving method comprising providing conversion using the AC/DC PFC conversion method of claim 8 , and driving an LED load using a converted DC voltage.