Output voltage control circuit of power converter for light-load power saving
A control circuit of a power converter for light-load power saving according to the present invention comprises a first feedback circuit coupled to an output voltage of the power converter to receive a first feedback signal. A second feedback circuit is coupled to the output voltage to receive a second feedback signal. A control circuit generates a switching signal for switching a transformer of the power converter and regulating the output voltage of the power converter in response to the first feedback signal and the second feedback signal. The switching signal is generated in accordance with the first feedback signal when an output load is high. The switching signal is generated in accordance with the second feedback signal during a light-load condition.
1. A control circuit of a power converter for light-load power saving comprising:
a first feedback circuit coupled to an output voltage of the power converter to receive a first feedback signal;
a second feedback circuit coupled to the output voltage to receive a second feedback signal; and
a control circuit generating a switching signal for switching a transformer of the power converter and regulating the output voltage of the power converter in response to the first feedback signal and the second feedback signal;
wherein the control circuit comprises a threshold circuit determining a light-load condition and generating a light-load signal in response to the first feedback signal and the second feedback signal; the switching signal is generated in accordance with the first feedback signal when an output load is high; the switching signal is generated in accordance with the second feedback signal during the light-load condition.
2. The control circuit as claimed in claim 1 , wherein the output voltage at the light-load condition is lower than the output voltage at a heavy-load.
3. The control circuit as claimed in claim 1 , wherein the output voltage controlled by the second feedback signal is lower than the output voltage controlled by the first feedback signal.
4. The control circuit as claimed in claim 1 , wherein the control circuit comprises:
an input circuit coupled to receive the first feedback signal and the second feedback signal for generating a feedback signal;
wherein the threshold circuit is coupled to receive the feedback signal for determining the light-load condition and generating the light-load signal.
5. The control circuit as claimed in claim 4 , wherein the control circuit further comprises a timer coupled to receive the light-load signal for generating a light-load enable signal, wherein the light-load enable signal is coupled to enable the second feedback signal.
6. The control circuit as claimed in claim 1 , wherein the control circuit comprises a soft-start circuit generating a soft-start signal, the switching signal is soft-started by the control circuit in accordance with the soft-start signal when the second feedback signal is disabled and the first feedback signal is enabled to control the switching signal.
7. The control circuit as claimed in claim 1 , wherein the first feedback circuit is coupled to the output voltage of the power converter to receive the first feedback signal through an optical coupler, and the second feedback circuit is coupled to the output voltage to receive the second feedback signal through a winding of the transformer of the power converter.
8. A method of light-load power saving for a power converter comprising:
generating a first feedback signal through an optical coupler;
generating a second feedback signal through a winding of a transformer;
determining a light-load condition and generating a light-load signal in response to the first feedback signal and the second feedback signal; and
generating a switching signal for switching the transformer and regulating an output voltage of the power converter in response to the first feedback signal and the second feedback signal;
wherein the switching signal is generated in accordance with the first feedback signal when an output load is high; the switching signal is generated in accordance with the second feedback signal during the light-load condition.
9. The method as claimed in claim 8 , wherein the switching signal is soft-started when the second feedback signal is disabled and the first feedback signal is enabled to control the switching signal.
10. The method as claimed in claim 8 , wherein the output voltage at the light-load condition is lower than the output voltage at a heavy-load.
11. The method as claimed in claim 8 , wherein the output voltage controlled by the second feedback signal is lower than the output voltage controlled by the first feedback signal.
12. The method as claimed in claim 8 , wherein the first feedback signal and the second feedback signal are generated in accordance with the output voltage of the power converter.
13. A control circuit of a power converter for light-load power saving comprising:
a first primary-side feedback circuit generating a first primary-side feedback signal through a winding of a transformer;
a second primary-side feedback circuit generating a second primary-side feedback signal through the winding of the transformer; and
a control circuit generating a switching signal for switching the transformer and regulating an output voltage of the power converter in response to the first primary-side feedback signal and the second primary-side feedback signal;
wherein the control circuit comprises a threshold circuit determining a light-load condition and generating a light-load signal in response to the first primary-side feedback signal and the second primary-side feedback signal; the switching signal is generated in accordance with the first primary-side feedback signal when an output load is high; the switching signal is generated in accordance with the second primary-side feedback signal during the light-load condition, the output voltage at light-load is lower than the output voltage at heavy-load.
14. The control circuit as claimed in claim 13 , wherein the control circuit comprises:
an input circuit generating a feedback signal in response to the first primary-side feedback signal and the second primary-side feedback signal; and
a timer coupled to receive the light-load signal for generating a light-load enable signal, wherein the light-load enable signal is coupled to enable the second primary-side feedback signal;
wherein the threshold circuit is coupled to receive the feedback signal for determining the light-load condition and generating the light-load signal.
15. The control circuit as claimed in claim 13 , wherein the first primary-side feedback circuit and the second primary-side feedback circuit generates the first primary-side feedback signal and the second primary-side feedback signal in accordance with the output voltage of the power converter.
16. The control circuit as claimed in claim 13 , wherein the control circuit comprises a soft-start circuit generating a soft-start signal, the switching signal is soft-started by the control circuit in accordance with the soft-start signal when the second primary-side feedback signal is disabled and the first primary-side feedback signal is enabled to control the switching signal.
17. A light-load power saving method for a primary-side control power converter comprising:
generating a first primary-side feedback signal and a second primary-side feedback signal through a winding of a transformer;
determining a light-load condition and generating a light-load signal in response to the first primary-side feedback signal and the second primary-side feedback signal; and
generating a switching signal for switching the transformer and regulating an output voltage of the power converter in response to the first primary-side feedback signal and the second primary-side feedback signal;
wherein the switching signal is generated in accordance with the first primary-side feedback signal when an output load is high; the switching signal is generated in accordance with the second primary-side feedback signal during the light-load condition, the output voltage at light-load is lower than the output voltage at heavy-load.
18. The light-load power saving method as claimed in claim 17 , wherein the switching signal is soft-started when the second primary-side feedback signal is disabled and the first primary-side feedback signal is enabled to control the switching signal.
19. The light-load power saving method as claimed in claim 17 , wherein a reference voltage of the second primary-side feedback signal is lower than a reference voltage of the first primary-side feedback signal.
20. The light-load power saving method as claimed in claim 17 , wherein the first primary-side feedback signal and the second primary-side feedback signal are generated in accordance with the output voltage of the power converter.