Apparatus and method for resonant converters

1. A converter comprising:

an input coupled to a power source;

a plurality of power switches coupled to the input;

a resonant tank coupled to the plurality of power switches; and

a controller coupled to the power switches, wherein the controller is configured to generate a plurality of gate drive signals for the power switches, and wherein the gate drive signals are arranged such that a switching frequency of the converter is in a frequency band, wherein the frequency band comprises an upper limit and a lower limit, and wherein the upper limit and the lower limit are adjacent to a resonant frequency of the resonant tank, and wherein the frequency band is determined through a control loop, and wherein a reference of the control loop is so arranged that the resonant frequency is within the frequency band, and wherein the reference follows a variable reference function, and wherein the variable reference function includes variables selected from the group consisting of an input voltage, an input current, an output voltage, an output current, an operating temperature.

2. The converter of claim 1 , wherein:

the frequency band includes the resonant frequency of the resonant tank; and

the gate drive signals are generated by varying the switching frequency of the converter from the resonant frequency of the resonant tank.

3. The converter of claim 1 , wherein:

in response to an input voltage change, the gate drive signals are generated by varying the switching frequency of the converter from a first switching frequency to a second switching frequency through a feed-forward control mechanism, and wherein the first switching frequency and the second switching frequency are within the frequency band.

4. The converter of claim 1 , wherein:

in response to an output voltage change, the gate drive signals are generated by varying the switching frequency of the converter from a first switching frequency to a second switching frequency through a feedback control mechanism, and wherein the first switching frequency and the second switching frequency are within the frequency band.

5. The converter of claim 1 , wherein:

in response to a load current change, the gate drive signals are generated by varying the switching frequency of the converter from a first switching frequency to a second switching frequency through a feedback control mechanism, and wherein the first switching frequency and the second switching frequency are within the frequency band.

6. The converter of claim 1 , wherein:

in response to a power change, the gate drive signals are generated by varying the switching frequency of the converter from a first switching frequency to a second switching frequency through a feedback control mechanism, and wherein the first switching frequency and the second switching frequency are within the frequency band.

7. A method comprising:

providing a resonant converter, wherein the resonant converter comprises:

an input coupled to a power source;

a plurality of power switches coupled to the input;

a resonant tank coupled to the plurality of power switches; and

a controller coupled to the power switches; and

generating a plurality of gate drive signals for the power switches, wherein the gate drive signals are arranged such that a switching frequency of the resonant converter is in a frequency band, wherein the frequency band comprises an upper limit and a lower limit, and wherein the upper limit and the lower limit are adjacent to a resonant frequency of the resonant tank, and wherein the frequency band is determined through a control loop, and wherein a reference of the control loop is so arranged that the resonant frequency is within the frequency band, and wherein the reference follows a variable reference function, and wherein the variable reference function includes variables selected from the group consisting of an input voltage, an input current, an output voltage, an output current, an operating temperature.

8. The method of claim 7 , further comprising:

operating the resonant converter in the frequency band, wherein the switching frequency of the resonant converter varies from a first switching frequency to a second switching frequency in response to an input voltage drop, and wherein:

the second switching frequency generates a second gain of the resonant converter; and

the first switching frequency generates a first gain of the resonant converter, and wherein:

the second gain is greater than the first gain; and

the second switching frequency is less than the upper limit of the frequency band.

9. The method of claim 7 , further comprising:

operating the resonant converter in the frequency band, wherein the switching frequency of the resonant converter varies from a first switching frequency to a second switching frequency in response to an input voltage increase, and wherein:

the first switching frequency generates a first gain of the resonant converter; and

the second switching frequency generates a second gain of the resonant converter, and wherein:

the first gain is greater than the second gain; and

the second switching frequency is greater than the lower limit of the frequency band.

10. The method of claim 7 , further comprising:

controlling the resonant converter through a feedback loop, wherein a reference of the feedback loop follows:

V

REF

⁡

(

w

)

=

w

2

·

L

m

·

C

r

·

R

eq

·

V

IN

(

w

2

·

L

m

·

C

r

+

w

2

·

L

r

·

C

r

-

1

)

2

·

R

eq

2

+

w

2

·

L

m

2

·

(

1

-

w

2

·

L

r

·

C

r

)

2

where w is an angular frequency of the switching frequency, Lm is a magnetizing inductance, Cr is a resonant capacitance of the resonant tank, Req is an equivalent resistor, VIN is an input voltage, Lr is a resonant inductance of the resonant tank.

11. The method of claim 10 , wherein:

the switching frequency is within the frequency band, and wherein the switching frequency is determined by a function.

12. A method comprising:

providing a resonant converter, wherein the resonant converter comprises:

a power stage comprising:

an input coupled to a power source;

a plurality of power switches coupled to the input;

a resonant tank coupled to the plurality of power switches;

an isolation device coupled to the resonant tank; and

an output coupled to the isolation device through a rectifier; and

a control stage coupled to the power switches, wherein the control stage receives signals from both the input and the output; and

generating a plurality of gate drive signals for the power switches, wherein the gate drive signals are arranged such that a switching frequency of the resonant converter is in a frequency band, wherein the frequency band comprises an upper limit and a lower limit, and wherein the upper limit and the lower limit are adjacent to a resonant frequency of the resonant tank, and wherein the frequency band is determined through a control loop, and wherein a reference of the control loop is so arranged that the resonant frequency is within the frequency band, and wherein the reference follows a variable reference function, and wherein the variable reference function includes variables selected from the group consisting of an input voltage, an input current, an output voltage, an output current, an operating temperature.

13. The method of claim 12 , wherein:

the frequency band includes the resonant frequency of the resonant tank; and

the frequency band is in a range from about 90% of the resonant frequency of the resonant tank to about 110% of the resonant frequency of the resonant tank.

14. The method of claim 12 , further comprising:

varying the switching frequency from a first switching frequency to a second switching frequency to achieve a better output voltage regulation, wherein the second switching frequency is within the frequency band.

15. The method of claim 12 , further comprising:

varying the switching frequency from a first switching frequency to a second switching frequency to achieve a better output current regulation, wherein the second switching frequency is within the frequency band.

16. The method of claim 12 , further comprising:

varying the switching frequency from a first switching frequency to a second switching frequency through a feedback control mechanism, wherein the second switching frequency is within the frequency band.

17. The method of claim 12 , further comprising:

varying the switching frequency from a first switching frequency to a second switching frequency through a feed-forward control mechanism, wherein the second switching frequency is within the frequency band.