SWITCHING POWER CONVERTER WITH PRIMARY-SIDE DYNAMIC LOAD DETECTION AND PRIMARY-SIDE FEEDBACK AND CONTROL

• US 20140362612A1
• Filed: 06/11/2013
• Published: 12/11/2014
• Est. Priority Date: 06/11/2013
• Status: Active Grant

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Shi, Fuqiang, Li, Yong, Kesterson, John William
• Granted Patent: US 9,184,667 B2
• Time in Patent Office: Days
• US Class Current: 363/21.16
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

A switching power converter provides regulated voltage to a load. The switching power converter comprises a transformer including a first primary winding coupled to an input voltage, a second primary winding, a secondary winding coupled to an output of the switching power converter, and an auxiliary winding, a first switch coupled to the first primary winding, and a second switch coupled to the secondary primary winding. A controller generates a first control signal to turn the first switch on or off at a first switching frequency, and a second control signal to turn the second switch on or off at a second switching frequency that is higher than the first frequency. During off cycles of the switches, feedback voltage representing the output voltage of the power converter is generated across the auxiliary winding. The controller controls switching of the first switch to regulate the output voltage based on the feedback.

Claims

1. A switching power converter comprising:

a transformer including a first primary winding coupled to an input voltage, a second primary winding, a secondary winding coupled to an output of the switching power converter, and an auxiliary winding on a primary side of the transformer, output voltage across the secondary winding being reflected as feedback voltage across the auxiliary winding;

a first switch coupled to the first primary winding of the transformer, current in the primary winding being generated responsive to the first switch being turned on and not generated responsive to the first switch being turned off, the feedback voltage being generated across the auxiliary winding during off-cycles of the first switch;

a second switch coupled to the second primary winding of the transformer, current in the second primary winding being generated responsive to the second switch being turned on and not being generated responsive to the second switch being turned off, the feedback voltage being also generated across the auxiliary winding during off-cycles of the second switch; and

a controller coupled to the first switch and the second switch, the controller being configured to generate a first control signal to turn on or turn off the first switch at a first switching frequency and a second control signal to turn on or turn off the second switch at a second switching frequency that is higher than the first frequency.

2. The switching power converter of claim 1, wherein the controller is further configured to regulate turning on or off the first switch at least in part based on the feedback voltage generated during off-cycles of the first switch and the second switch at the second frequency.

3. The switching power converter of claim 1, wherein the second switch is powered by a voltage that is lower than the input voltage.

4. The switching power converter of claim 3, further comprising a capacitor coupled to the auxiliary winding, the capacitor being charged during the off-cycles of the first switch and the second switch, and the second switch being powered by a voltage across the capacitor.

5. The switching power converter of claim 4, wherein a first switching loss during one switching cycle of the first switch is larger than a second switching loss during one switching cycle of the second switch.

6. The switching power converter of claim 1, wherein the controller is configured to generate the second control signal, while the controller generates the first control signal to control the first switch using pulse frequency modulation.

7. The switching power converter of claim 1, wherein the controller is configured to generate the second control signal, responsive to the first switching frequency dropping below a predetermined threshold.

8. The switching power converter of claim 1, wherein the controller is configured to receive the feedback voltage multiple times during a single off-cycle of the first switch.

9. A switching power converter comprising:

a transformer including a primary winding coupled to an input voltage, a secondary winding coupled to an output of the switching power converter, and an auxiliary winding on a primary side of the transformer, output voltage across the secondary winding being reflected as feedback voltage across the auxiliary winding;

a switch coupled to the primary winding of the transformer, current in the primary winding being generated responsive to the switch being turned on and not generated responsive to the switch being turned off;

a controller coupled to the switch and configured to generate a control signal to turn on or turn off the switch at a switching frequency,

wherein the controller is further configured to determine the feedback voltage multiple times during a single off-cycle of the switch.

10. A method for controlling a switching power converter, the switching power converter including a transformer with a first primary winding coupled to an input voltage, a second primary winding, a secondary winding coupled to an output of the switching power converter, and an auxiliary winding on a primary side of the transformer, output voltage across the secondary winding being reflected as feedback voltage across the auxiliary winding, a first switch coupled to the first primary winding of the transformer, and a second switch coupled to the second primary winding of the transformer, the method comprising:

generating a first control signal to turn on or turn off the first switch at a first switching frequency;

generating a second control signal to turn on or turn off the second switch at a second switching frequency that is higher than the first switching frequency; and

determining the feedback voltage in each off cycle of the second switch.

11. The method of claim 10, further comprising regulating turning on or off the first switch based at least in part on the feedback voltage generated during off-cycles of the first switch and the second switch at the second frequency.

12. The method of claim 10, wherein the second switch is powered by a voltage that is lower than the input voltage.

13. The method of claim 12, wherein the switching power converter further comprises a capacitor coupled to the auxiliary winding, and the method further comprises charging the capacitor during the off-cycles of the first switch and the second switch, the second switch being powered by the voltage across the capacitor.

14. The method of claim 13, wherein a first switching loss during one switching cycle of the first switch is larger than a second switching loss during one switching cycle of the second switch.

15. The method of claim 10, further comprising generating the second control signal, while generating the first control signal to control the first switch using pulse frequency modulation.

16. The method of claim 10, wherein the second control signal is generated responsive to the first switching frequency dropping below a predetermined threshold.

17. The method of claim 10, further comprising receiving the feedback voltage multiple times during a single off-cycle of the first switch.

18. A method for controlling a switching power converter, the switching power converter including a transformer with a first primary winding coupled to an input voltage, a second primary winding, a secondary winding coupled to an output of the switching power converter, and an auxiliary winding on a primary side of the transformer, output voltage across the secondary winding being reflected as feedback voltage across the auxiliary winding, the switching power converter also including a switch coupled to the first primary winding of the transformer, the method comprising:

generating a control signal to turn on and turn off the switch at a switching frequency; and

determining the feedback voltage multiple times during a single off-cycle of the switch.