ADAPTIVE ACTIVE CLAMP OF FLYBACK POWER CONVERTER WITH HIGH EFFICIENCY FOR HEAVY LOAD AND LIGHT LOAD

• US 20140233275A1
• Filed: 02/18/2014
• Published: 08/21/2014
• Est. Priority Date: 02/18/2013
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: System General Corporation (ON Semiconductor Corporation)
• Inventors: YANG, TA-YUNG, HSIEH, CHIH-HSIEN, CHEN, JUNG-SHENG, WEI, KAI-FANG
• Granted Patent: US 9,252,676 B2
• Time in Patent Office: Days
• US Class Current: 363/21.17
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A control circuit of a flyback power converter according to the present invention comprises a low-side transistor, an active-damper, a high-side drive circuit, and a controller. The low-side transistor is coupled to switch a transformer. The active-damper is coupled in parallel with the transformer. The high-side drive circuit is coupled to drive the active-clamper. The controller generates a switching signal and an active-clamp signal. The switching signal is coupled to drive the low-side transistor. The switching signal is generated in accordance with a feedback signal for regulating an output of the flyback power converter. The active-clamp signal is coupled to control the high-side drive circuit and the active-damper. The active-clamp signal is generated in response to a demagnetizing time of the transformer. The pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition.

Claims

1. A control circuit of a flyback power converter, comprising:

a low-side transistor coupled to switch a transformer;

an active-damper coupled in parallel with the transformer;

a high-side drive circuit coupled to drive the active-damper; and

a controller generating a switching signal and an active-clamp signal;

wherein the switching signal is coupled to drive the low-side transistor;

the switching signal is generated in accordance with a feedback signal for regulating an output of the flyback power converter;

the active-clamp signal is coupled to control the high-side drive circuit and the active-damper;

the active-clamp signal is generated in response to a demagnetizing time of the transformer;

the pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition.

2. The control circuit as claimed in claim 1, wherein the active-damper comprises a high-side transistor connected in series with a capacitor, the high-side drive circuit is coupled to drive the high-side transistor.

3. The control circuit as claimed in claim 1, wherein the active-clamp signal is generated in accordance with a reflected signal of the transformer.

4. The control circuit as claimed in claim 1, wherein the pulse width of the active-clamp signal is correlated to the demagnetizing time of the transformer.

5. The control circuit as claimed in claim 1, wherein the controller generates the switching signal in response to the demagnetizing time of the transformer.

6. The control circuit as claimed in claim 1, wherein the controller includes:

a discharge-time signal generation circuit generating a discharge-time signal in response to a reflected signal of the transformer;

in which the discharge-time signal is related to the demagnetizing time of the transformer;

a turn-on circuit generating a turn-on signal in response to the discharge-time signal for generating the switching signal; and

an active-clamp signal generation circuit generating the active-clamp signal in response to the discharge-time signal.

7. The control circuit as claimed in claim 1, wherein the switching signal is enabled in response to a clock signal in a CCM operation;

the clock signal is generated by an oscillation circuit of the controller.

8. The control circuit as claimed in claim 1, wherein the active-clamp signal is disabled in response to a pulse signal in a CCM operation;

the pulse signal is generated by an oscillation circuit of the controller;

the pulse signal is correlated to a clock signal generated by the oscillation circuit.

9. A method for controlling a flyback power converter with an active-damper, comprising:

generating a switching signal in accordance with a feedback signal for switching a low-side transistor and regulating an output of the flyback power converter; and

generating an active-clamp signal in accordance with a demagnetizing time of a transformer;

wherein the pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition;

the low-side transistor is coupled to switch the transformer;

the active-clamp signal is coupled to drive the active-damper, the active-damper is coupled in parallel with the transformer.

10. The method as claimed in claim 9, wherein the active-clamp signal is generated in accordance with a reflected signal of the transformer.

11. The method as claimed in claim 9, wherein the switching signal is generated in response to the demagnetizing time of the transformer.

12. The method as claimed in claim 9, wherein the switching signal is enabled in response to a clock signal in a CCM operation;

the clock signal is generated by an oscillation circuit.

13. The method as claimed in claim 9, wherein the active-clamp signal is disabled in response to a pulse signal in a CCM operation;

the pulse signal is correlated to a clock signal.

14. A control circuit of an active clamp flyback power converter, comprising:

a low-side transistor coupled to switch a transformer;

an active-damper coupled in parallel with the transformer;

a high-side drive circuit coupled to drive the active-damper; and

a controller generating a switching signal and an active-clamp signal;

wherein the switching signal is coupled to drive the low-side transistor;

the switching signal is generated in accordance with a feedback signal for regulating an output of the active clamp flyback power converter;

the active-clamp signal is coupled to control the high-side drive circuit and the active-damper;

the pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition.

15. The control circuit as claimed in claim 14, wherein the pulse width of the active-clamp signal is correlated to a demagnetizing time of the transformer.

16. The control circuit as claimed in claim 14, wherein the controller generates the switching signal in response to a demagnetizing time of the transformer.