Method and apparatus for fault detection in a switching power supply

• US 20070002510A1
• Filed: 07/01/2005
• Published: 01/04/2007
• Est. Priority Date: 07/01/2005
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Polivka, William M., Baurle, Stefan
• Granted Patent: US 7,539,028 B2
• Time in Patent Office: Days
• US Class Current: 361/94
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

Techniques are disclosed to detect a fault in the feedback circuit of a switching power supply while the power supply operates in a mode where the output is below its regulated value. The power supply delivers maximum power at a given switching frequency without a feedback signal while the output is below its regulated value. A fault protection circuit substantially reduces the average output power if there is no feedback signal for the duration of a fault time. When there is no feedback signal, the power supply increases the maximum output power by increasing the switching frequency before the end of the fault time to increase the output to a regulated value. The presence of a feedback signal when the output reaches a regulated value restores the original switching frequency and returns the output to its unregulated value. The absence of a feedback signal at the end of the fault time engages the fault protection circuit to substantially reduce the output power.

Claims

1. A switching regulator circuit, comprising:

a switch to be coupled to an energy transfer element of a power supply;

a feedback circuit coupled to the controller and coupled to receive a feedback signal from an output of the power supply;

a controller coupled to the switch and to the feedback circuit to control a switching of the switch to regulate a combination of an output voltage and an output current at the output of the power supply, wherein combinations of the output voltage and the output current correspond to output regions such that there is at least one regulated output region and one unregulated output region, the controller including an oscillator having first and second switching frequencies, wherein the second switching frequency is greater than the first switching frequency, the controller further including a fault detection circuit having a fault timer to measure a duration of an absence of an adequate feedback signal, the fault detection circuit having a fault mode of operation and a feedback check mode of operation, the fault mode of operation to substantially reduce an average power at the output of the power supply when the feedback signal is absent longer than a fault time, the feedback check mode of operation to raise the switching frequency from the first switching frequency to the second frequency when the feedback signal is absent for a duration less than the fault time.

2. The switching regulator of claim 1 wherein the switching regulator is included in a battery charger.

3. The switching regulator of claim 1 wherein the controller includes an integrated circuit.

4. The switching regulator of claim 1 wherein the controller includes discrete electrical components.

5. A method, comprising:

measuring a feedback signal received from an output of a power supply to control an output power of the power supply;

operating the power supply in an unregulated feedback check mode after an adequate feedback signal is not present for a first duration;

operating the power supply in an unregulated auto-restart mode if an adequate feedback signal is not present for a second duration greater than the first duration.

6. The method of claim 5 further comprising increasing a switching frequency during the unregulated feedback check mode.

7. The method of claim 5 further comprising measuring a duration of time that the adequate feedback signal is not present.

8. The method of claim 5 further comprising moving an operating point of the power supply from an unregulated condition to a regulated current operating point by increasing output power of the power supply.

9. The method of claim 5 further comprising moving an operating point of the power supply from an unregulated condition to a regulated voltage operating point by increasing output power of the power supply.

10. The method of claim 5 further comprising adjusting a maximum power output power of the power supply in response to a switching frequency of the power supply.