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1. (WO2017167640) AN AC/DC PFC CONVERTER USING A HALF BRIDGE RESONANT CONVERTER, AND CORRESPONDING CONVERSION METHOD
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CLAIMS:

1. An AC/DC PFC converter, comprising:

a PFC pre-regulator (110), comprising:

an AC input;

a rectifier (12) for rectifying a mains voltage (10);

a half bridge inverter comprising a high side switch (28) and a low side switch (30), wherein an output is defined from a node between the switches;

an LLC circuit (20,24,26,27) coupled to the output; and

a control circuit (112) for generating a gate drive signal for controlling the switching of the high side and low side switches thereby to generate a controlled output voltage (vbus), 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; and

an output stage, comprising:

a DC/DC converter (116);

a feedback unit (118) adapted to provide a feedback signal to the control circuit of the PFC pre-regulator (110) for modulating the controlled output voltage (vbus) of the PFC pre-regulator (110) in dependence on at least the output power of the output stage, wherein a set-point for the controlled output voltage is varied synchronously with the mains voltage.

2. A converter as claimed in claim 1, wherein the control circuit (112) is for generating a gate drive signal in dependence on an electrical feedback parameter from the LLC circuit.

3. A converter as claimed in claim 2, wherein the control circuit (112) is adapted to set a threshold level for the electrical feedback parameter in dependence on the feedback signal and the rectified input voltage without measurement of the input current.

4. A converter as claimed in claim 3, wherein the electrical feedback parameter comprises a voltage (vC) across a capacitor of the LLC circuit, which is representative of the input current.

5. A converter as claimed in claim 4, wherein the control circuit is adapted to compare the voltage across the capacitor of the LLC circuit with a threshold at a switching instant of the gate drive signal.

6. A converter as claimed in any preceding claim, wherein the output stage (116) is a switch mode power converter.

7. A converter as claimed in claim 6, wherein the output stage is a buck converter.

8. A converter as claimed in any preceding claim, wherein the feedback unit

(118) is adapted to provide a feedback signal to the control circuit (112) of the PFC pre-regulator for modulating the controlled output voltage of the PFC pre-regulator in dependence on the amplitude and phase of the input voltage and the output power.

9. A converter as claimed in claim 8, wherein the amplitude and phase of the input voltage are derived by the feedback unit (118) from the frequency of a high frequency ripple on the controlled output voltage (vbus).

10. A converter as claimed in claim 8, wherein the amplitude and phase of the input voltage are derived by the feedback unit (118) based on a feedforward signal from the

PFC pre-regulator.

11. A converter as claimed in any preceding claim, wherein the control unit comprises an oscillator and controls the oscillation frequency or the control unit comprises a latch and controls the timing of the latch switching.

12. An LED driver, comprising:

an AC/DC PFC converter as claimed in any preceding claim.

13. An AC/DC PFC conversion method, comprising:

operating a PFC pre-regulator by:

rectifying a mains voltage;

controlling a half bridge inverter comprising a high side switch and a low side switch by generating a gate drive signal and providing an output from a node between the switches to an LLC circuit thereby to generate a controlled output voltage, wherein a high gate drive signal turns on one switch and turns off the other and a low gate drive signal turns off the one switch and turns on the other switch; and

providing an output from the LLC circuit to an output stage; and operating the output stage by:

implementing DC/DC conversion; and

providing a feedback signal from the output stage to the PFC pre-regulator for modulating the controlled output voltage of the PFC pre-regulator in dependence on at least the output power of the output stage, wherein a set-point for the controlled output voltage is varied synchronously with the mains voltage.

14. A method as claimed in claim 13, comprising providing a feedback signal to the PFC pre-regulator for modulating the controlled output voltage of the PFC pre-regulator also in dependence on amplitude and phase of the input voltage.

15. A method as claimed in claim 14, comprising deriving the amplitude and phase of the AC input:

from the frequency of a high frequency ripple on the controlled output voltage or

from a feedforward signal from the PFC pre-regulator.