Method and apparatus for reducing audio noise in a switching regulator

• US 6,667,605 B2
• Filed: 10/30/2002
• Issued: 12/23/2003
• Est. Priority Date: 08/08/2000
• Status: Expired due to Fees

• Current Assignee: Power Integrations Incorporated
• Original Assignee: Power Integrations Incorporated
• Inventors: Wong, Kent, Balakrishnan, Balu, Djenguerian, Alex B.
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US10/285,266
• Publication Number:
  US 20030062879A1
• Time in Patent Office: 419 Days
• Field of Search: 323/277, 323/272, 323/282, 323/284, 323/285, 323/288, 323/283, 363/16, 363/18, 363/20, 363/97, 363/131, 363/132
• US Class Current: 323/277
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 1/0032 Control circuits allowing low power mode operation, e.g. in standby mode
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• 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
• CPC Class Codes: H02M 3/33515 with digital control
• 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 switching regulator utilizing on/off control that reduces audio noise at light loads by adjusting the current limit of the switching regulator. In one embodiment, a switching regulator includes a state machine that adjusts the current limit of the switching regulator based on a pattern of feedback signal values from the output of the power supply for a preceding N cycles of the drive signal. The state machine adjusts the current limit lower at light loads such that cycles are not skipped to reduce the operating frequency of the switching regulator into the audio frequency range until the flux density through the transformer is sufficiently low to reduce the generation of audio noise.

Claims

1. A switching regulator, comprising:

a power switch coupled between first and second terminals, the first terminal to be coupled to an energy transfer element of a power supply and the second terminal to be coupled to a supply rail of the power supply;

a drive signal generator circuit coupled to a third terminal to receive an input signal, the drive signal generator to generate a drive signal coupled to control switching of the power switch responsive to the input signal, the drive signal generator circuit to selectively disable each on period of the drive signal in response to the input signal to regulate the output of the power supply; and

a current limit circuit coupled to the power switch and the drive signal generator circuit to control the drive signal to limit a current flow through the power switch, the current limit circuit having a plurality of current limit settings for the power switch selected responsive to the input signal.

2. The switching regulator of claim 1 wherein the input signal is a feedback signal representative of an output of the power supply.

3. The switching regulator of claim 1 wherein the input signal is a feedback signal representative of an output voltage of the power supply.

4. The switching regulator of claim 1 wherein the input signal is a feedback signal representative of an output current of the power supply.

5. A power supply, comprising:

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

a power switch coupled between the energy transfer element input and a supply rail of the power supply;

a drive signal generator circuit coupled to receive an input signal, the drive signal generator to generate a drive signal coupled to control switching of the power switch responsive to the input signal, the drive signal generator circuit to selectively disable each on period of the drive signal in response to the input signal to regulate the output of the power supply; and

a current limit circuit coupled to the power switch and the drive signal generator circuit to control the drive signal to limit a current flow through the power switch, the current limit circuit having a plurality of current limit settings for the power switch selected responsive to the input signal.

6. The power supply of claim 5 wherein the input signal is a feedback signal representative of an output of the power supply.

7. The power supply of claim 5 wherein the input signal is a feedback signal representative of an output voltage of the power supply.

8. The power supply of claim 5 wherein the input signal is a feedback signal representative of an output current of the power supply.