Method and apparatus to limit maximum switch current in a switching power supply

• US 20070008756A1
• Filed: 07/08/2005
• Published: 01/11/2007
• Est. Priority Date: 07/08/2005
• Status: Active Grant

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Djenguerian, Alex, Morrish, Andrew
• Granted Patent: US 7,593,245 B2
• Time in Patent Office: Days
• US Class Current: 363/95
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/0038 Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• 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 limit the current in a switch of a switching power supply. An example switching regulator circuit includes a power switch to be coupled to an energy transfer element of a power supply. A controller to generate a drive signal is coupled to be received by the power switch to control the switching of the power switch. A short on time detector is included in the controller. The short on time detector is to detect an occurrence of a threshold number of one or more consecutive short on times of the switch. A frequency adjuster is also included in the controller and coupled to the short on time detector. The frequency adjuster is to adjust an oscillating frequency of an oscillator included in the controller in response to the short on time detector.

Claims

1. A switching regulator circuit, comprising:

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

a controller to generate a drive signal coupled to be received by the switch to control switching of the switch;

a short on time detector included in the controller and coupled to detect an occurrence of a threshold number of one or more consecutive short on times of the switch; and

a frequency adjuster included in the controller and coupled to the short on time detector, the frequency adjuster to adjust an oscillating frequency of an oscillator included in the controller in response to the short on time detector.

2. The switching regulator of claim 1 wherein the frequency adjuster is to reduce the frequency of the oscillator to delay a next pulse in a drive signal coupled to be received by the switch in response to the detection of the occurrence of the threshold number of one or more consecutive short on times of the switch.

3. The switching regulator of claim 1 wherein the frequency adjuster is to reduce the frequency of the oscillator to skip a next one or more pulses in a drive signal coupled to be received by the switch in response to the detection of the occurrence of the threshold number of one or more consecutive short on times of the switch.

4. The switching regulator of claim 1 wherein the controller is included in an integrated circuit.

5. The switching regulator of claim 4 wherein the switch is included in the integrated circuit.

6. The switching regulator of claim 1 wherein the controller is to be coupled to receive a feedback signal from an output of the power supply, the controller to generate a drive signal coupled to be received by the switch to control switching of the switch to regulate the output of the power supply.

7. The switching regulator of claim 1 further comprising a current sensor included in the controller and coupled to detect an excess current through the switch.

8. The switching regulator of claim 7 further comprising a leading edge blanking circuit included in the controller and coupled to the current sensor.

9. The switching regulator of claim 8 wherein a short on time of the switch is slightly greater than a sum of leading edge blanking time and a current limit delay time.

10. A method for regulating a power supply, comprising:

switching a switch coupled to an energy transfer element at an input of a power supply in response to a drive signal responsive to feedback received from an output the power supply;

detecting an occurrence of a threshold number of one or more consecutive short on times of the switch; and

delaying a next pulse of a drive signal coupled to be received by the switch in response to the occurrence of the threshold number of one or more consecutive short on times of the switch.

11. The method for regulating the power supply of claim 10 wherein delaying the next pulse of the drive signal in response to the occurrence of the threshold number of one or more consecutive short on times of the switch comprises adjusting a frequency of an oscillating signal from which the drive signal is generated.

12. The method for regulating the power supply of claim 10 wherein delaying the next pulse of the drive signal in response to the occurrence of the threshold number of one or more consecutive short on times of the switch comprises skipping a next pulse in the drive signal.

13. The method for regulating the power supply of claim 10 wherein detecting the occurrence of a threshold number of one or more consecutive short on times of the switch comprises detecting a pulse in the drive signal having an on time approximately equal to a sum of a leading edge blanking time and a current limit delay time.

14. A power supply, comprising:

an energy transfer element coupled between an input and an output of the power supply;

a switch coupled to the input of the energy transfer element to regulate a transfer of energy from the input of the power supply to the output of the power supply;

a controller including an oscillator to generate a drive signal received by the switch to control switching of the switch;

a short on time detector included in the controller and coupled to detect an occurrence of a threshold number of one or more consecutive short on times of the switch; and

a frequency adjuster included in the controller and coupled to the short on time detector and coupled to the oscillator, the frequency adjuster to adjust an oscillating frequency of the oscillator in response to the short on time detector.

15. The power supply of claim 14 further comprising a feedback circuit coupled between the output of the power supply and the controller to provide a feedback signal from the output of the power supply to the controller.

16. The power supply of claim 14 further comprising a current sense circuit included in the controller to limit a current through the switch.

17. The power supply of claim 14 further comprising an integrated circuit including the controller.

18. The power supply of claim 17 wherein the integrated circuit further includes the switch.