System and method for controlling voltage control loop in power converter

1. A circuit for controlling a power converter, the circuit comprising:

a transient detector configured to generate a transient detection signal in response to a feedback signal indicating an output signal of the power converter, the transient detection signal indicating that a value of the feedback signal is in a first range and a slope of the feedback signal is substantially equal to zero;

a gain selector configured to generate a gain selection signal in response to the transient detection signal; and

an amplifier circuit configured to generate a comparison signal based on the value of the feedback signal, a value of a reference signal, and a gain value of the amplifier circuit, the gain value being adjusted in response to the gain selection signal at a plurality of times when the power converter operates in a transient mode.

2. The circuit of claim 1 , wherein the amplifier circuit is a variable-gain non-linear amplifier including a plurality of transconductance amplifiers.

3. The circuit of claim 2 , wherein the gain value of the amplifier circuit has a first value when the value of the feedback signal is in the first range and a second value when the value of the feedback signal is in a second range, the first value being less than the second value.

4. The circuit of claim 2 , wherein the first range of the feedback signal is from a lower threshold voltage to an upper threshold voltage, and

wherein the plurality of transconductance amplifiers includes a first transconductance amplifier having a negative input coupled to a first reference voltage and a positive input coupled to the feedback signal, the first transconductance amplifier beginning to sink a current when the feedback voltage is equal to the lower threshold voltage.

5. The circuit of claim 4 , wherein the plurality of transconductance amplifiers further includes a second transconductance amplifier having a negative input coupled to a second reference voltage and a positive input coupled to the feedback voltage, the second transconductance amplifier sinking a maximum current when the feedback voltage is equal to the lower threshold voltage.

6. The circuit of claim 5 , wherein the plurality of transconductance amplifiers further includes a third transconductance amplifier having a negative input coupled to a third reference voltage and a positive input coupled to the feedback voltage, the third transconductance amplifier beginning to sink a current when the feedback voltage is equal to the upper threshold voltage.

7. The circuit of claim 1 , wherein the transient detector asserts the transient detection signal a given delay after the slope of the feedback signal becomes substantially equal to zero.

8. The circuit of claim 1 , wherein the plurality of times is a first plurality of times, and the gain value of the amplifier circuit decreases at the first plurality of times respectively corresponding to a plurality of points of the feedback signal when the value of the feedback signal decreases in the first range.

9. The circuit of claim 8 , wherein the first plurality of times are respectively associated with a second plurality of times, the feedback signal having a plurality of peaks at the second plurality of times.

10. The circuit of claim 1 , further comprising:

a capacitor having a first end coupled to an output of the amplifier circuit and a second end coupled to ground; and

a resistor having a first end coupled to the output of the amplifier circuit and a second end coupled to the first end of the capacitor.

11. The circuit of claim 1 , wherein the gain selector adjusts a value of the gain selection signal at the plurality of times, the plurality of times being in a range from 2 times to 9 times.

12. The circuit of claim 1 , wherein each of the plurality of times at which the gain value is adjusted lies within a time interval when the value of the feedback signal decreases in the first range.

13. A method for controlling a power converter, the method comprising:

generating a transient detection signal in response to a feedback signal indicating an output signal of the power converter, the transient detection signal indicating that a value of the feedback signal is in a first range and a slope of the feedback signal is substantially equal to zero;

generating a gain selection signal in response to the transient detection signal; and

generating a comparison signal based on the value of the feedback signal, a value of a reference signal, and a gain value of an amplifier circuit, the gain value being adjusted in response to the gain selection signal at a plurality of times when the power converter operates in a transient mode.

14. The method of claim 13 , wherein the amplifier circuit includes a first transconductance amplifier and the first range of the feedback signal is from a lower threshold voltage to an upper threshold voltage, and

wherein generating the comparison signal includes beginning to sink a current by the first transconductance amplifier when the feedback voltage is equal to the lower threshold voltage.

15. The method of claim 14 , wherein the amplifier circuit further includes a second transconductance amplifier, and

wherein generating the comparison signal further includes sinking a maximum current by the second transconductance amplifier when the feedback voltage is equal to the lower threshold voltage.

16. The method of claim 15 , wherein the amplifier circuit further includes a third transconductance amplifier, and

wherein generating the comparison signal further includes beginning to sink a current by the third transconductance amplifier when the feedback voltage is equal to the upper threshold voltage.

17. The method of claim 13 , wherein the plurality of times is a first plurality of times, the method further comprising decreasing the gain value of the amplifier circuit at the first plurality of times respectively corresponding to a plurality of points of the feedback signal when the value of the feedback signal decreases in the first range.

18. The method of claim 17 , wherein the first plurality of times are respectively associated with a second plurality of times, the feedback signal having a plurality of peaks at the second plurality of times.

19. A power converter comprising:

a current control loop performing a power factor correction (PFC) operation; and

a voltage control loop regulating a level of an output voltage, the voltage control loop including a voltage controller configured to generate a comparison signal indicating a difference between a reference voltage and a feedback voltage, the feedback voltage indicating the output voltage,

wherein the voltage controller comprises:

a transient detector configured to generate a transient detection signal in response to the feedback voltage, the transient detection signal indicating that a value of the feedback voltage is in a first range and a slope of the feedback voltage is substantially equal to zero;

a gain selector configured to generate a gain selection signal in response to the transient detection signal; and

an amplifier circuit generating a comparison signal based the value of the feedback voltage, the reference voltage, and a gain value of the amplifier circuit, the gain value being adjusted in response to the gain selection signal at a plurality of times when the power converter operates in a transient mode.

20. The power converter of claim 19 , wherein the transient detector asserts the transient detection signal a given delay after the slope of the feedback signal becomes substantially equal to zero.