Half bridge resonant converters, circuits using them, and corresponding control methods

1. A half bridge resonant converter, comprising:

a pair of DC voltage lines comprising a high voltage line and a low voltage line;

a half bridge inverter comprising a high side switch and a low side switch in series between the high voltage line and the low voltage line, wherein an output of the half bridge inverter is defined from a node (X) between the high side switch and the low side switch;

a resonant circuit coupled to the output of the half bridge inverter via a series output capacitor;

a first generating circuit for generating a first supply voltage from the high voltage line and from a voltage at the node (X) wherein the first generating circuit comprises:

a first input for receiving a voltage between the node (X) and the resonant circuit;

a charge pump circuit for converting an AC voltage at the first input into a DC voltage and storing it on a first output capacitor (Co) as an output of the first generating circuit at the first supply voltage; and

a supply transistor between the high voltage line and the output of the first generating circuit for charging the output capacitor (Co) before a start-of-oscillation occurs;

a second generating circuit for generating a second supply voltage from the low voltage line and from the voltage at the node (X);

a first control circuit for generating a gate drive signal for controlling the switching of the high side switch in dependence on an electrical feedback parameter, wherein the first control circuit has as its reference voltage supply the voltage at the node (X) and the first supply voltage greater than the voltage at the node; and

a second control circuit for generating a gate drive signal for controlling the switching of the low side switch in dependence on the electrical feedback parameter, wherein the second control circuit has as its reference voltage supply the low voltage line and the second supply voltage greater than the voltage at the low voltage line.

2. A converter as claimed in claim 1 , wherein the second generating circuit comprises:

a second input for receiving a voltage between the resonant circuit and the low voltage line;

a charge pump circuit for converting the AC voltage at the second input into a DC voltage and storing it on a second output capacitor as the output of the second generating circuit at the second supply voltage; and

a supply transistor between the node between the high side switch and the low side switch and the output of the second generating circuit.

3. A converter as claimed claim 1 , wherein the first control circuit comprises:

a first end of slope detection circuit having as input the high voltage line;

a first latch element triggered by the end of slope detection circuit and which generates a first control signal for switching the high side switch to a first state; and

a first signal generator for generating a second control signal for switching the high side switch to a second state.

4. A converter as claimed in claim 3 , wherein the first signal generator has a reference input for controlling the duration of the first state.

5. A converter as claimed in claim 1 , wherein the second control circuit comprises:

a second end of slope detection circuit having as input the node between the high side switch and the low side switch;

a second latch element triggered by the end of slope detection circuit and which generates a third control signal for switching the low side switch to a first state; and

a second signal generator for generating a fourth control signal for switching the low side switch to a second state.

6. A converter as claimed in claim 5 , wherein the second signal generator has a feedback control input for controlling the duration of the first state in dependence on the electrical feedback parameter.

7. A converter as claimed in claim 1 , wherein the electrical feedback parameter comprises a voltage which is dependent on the output current delivered by the converter to a load.

8. A converter as claimed in claim 1 , wherein the resonant circuit comprises an LLC circuit.

9. A converter as claimed in claim 1 , wherein the first and second control circuits each comprise an integrated circuit, for example integrated circuits of the same type.

10. An apparatus comprising:

the converter as claimed in claim 1 ; and

an output load.

11. An apparatus as claimed in claim 10 wherein the output load is an LED arrangement of one or more LEDs.

12. A conversion method, comprising:

operating a half bridge inverter comprising a high side switch and a low side switch between a DC high voltage line and a DC low voltage line, using a gate drive signal and providing an output from a node between the high side switch and the low side switch;

providing the output of the half bridge inverter to a resonant circuit via a series output capacitor;

generating a gate drive signal using a first control circuit, for controlling the switching of the high side switch in dependence on an electrical feedback parameter, wherein the first control circuit has as its reference voltage supply a voltage at the node between the high side switch and the low side switch and a first supply voltage greater than the voltage at the node between the high side switch and the low side switch;

generating the first supply voltage from the DC high voltage line and from the voltage at the node comprising the following method steps:

receiving a voltage between the node and the resonant circuit;

converting an AC voltage between the node and the resonant circuit at a first input into a DC voltage and storing it on a first output capacitor as an output via a charge pump;

charging the output capacitor before a start-of-oscillation occurs via a supply transistor; and

generating a gate drive signal using a second control circuit, for controlling the switching of the low side switch in dependence on the electrical feedback parameter, wherein the second control circuit has as its reference voltage supply the low voltage line and a second supply voltage greater than the voltage at the low voltage line.

13. A method as claimed in claim 12 , further comprising generating the first supply voltage from the high voltage line and from the voltage at node between the high side switch and the low side switch, and generating the second supply voltage from the low voltage line and from the voltage at node between the high side switch and the low side switch.