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(12) United States Patent
Balakrishnan et al.
(io) Patent No.: (45) Date of Patent:
US 7,400,122 B2 *Jul. 15, 2008
(54) METHOD AND APPARATUS FOR REDUCING AUDIO NOISE IN A SWITCHING REGULATOR
(75) Inventors: Balu Balakrishnan, Saratoga, CA (US);
Alex B. Djenguerian, Saratoga, CA
(US); Kent Wong, Fremont, CA (US)
(73) Assignee: Power Integrations, Inc., San Jose, CA (US)
( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.
This patent is subject to a terminal disclaimer.
(21) Appl.No.: 11/729,262
(22) Filed: Mar. 27, 2007
Related U.S. Application Data
Continuation of application No. 11/404,688, filed on Apr. 14, 2006, now Pat. No. 7,211,991, which is a continuation of application No. 11/100,065, filed on Apr. 5, 2005, now Pat. No. 7,045,994, which is a continuation of application No. 10/888,782, filed on Jul. 8, 2004, now Pat. No. 6,900,622, which is a continuation of application No. 10/659,911, filed on Sep. 11,2003, now Pat. No. 6,784,646, which is a continuation of application No. 10/285,266, filed on Oct. 30, 2002, now Pat. No. 6,667,605, which is a continuation of application No. 09/634,237, filedonAug. 8,2000, now Pat. No. 6,525,514.
(58) Field of Classification Search 323/282 286,
323/266-272, 222; 363/17, 19, 49, 97-98,
See application file for complete search history. (56) References Cited
U.S. PATENT DOCUMENTS
3,978,393 A 8/1976 Wisneretal.
FOREIGN PATENT DOCUMENTS
EP 0875983 A 11/1998
Power Integrations, Inc. "TinySwitch Family," TNY253-254-255, product information, pp. 1-16, (Feb. 1999).
Primary Examiner—Rajnikant B Patel
(74) Attorney, Agent, or Firm—Blakely Sokoloff Taylor &
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.
10 Claims, 9 Drawing Sheets