AN4148 FAIRCHILD | Alldatasheet
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Technical content
Audible Noise Reduction Techniques for FPS
Applications
www.fairchildsemi.com ©2005 Fairchild Semiconductor Corporation Rev. 1.0.0 1. Introduction In general, switched mode power supplies do not generate audible noise when they operate at constant ultrasonic frequencies (>20kHz). However, some switched mode power supplies can produce audible noise at certain load conditions. Most Fairchild Po wer Switches are designed to enter into burst switching operation at light load conditions to reduce standby consumption, which can cause audible noise when the fundamental frequency of the burst switching bundles is in the range of human hearing as shown in Figure This application note explains the major sources of audible noise and offers useful tips to engineers to solve the audible noise problem in their Fairchild Power Switch (FPS) applications. Figure 1. Burst Switching Operation vibration in the coils, ferrite cores or isolation tapes. snubber network should be examined.
- Techniques to Reduce the Audible
of the transformer elements as well. constant, which results in reduced audible noise. levels are determined by the feedback voltage level.
9/9/05 0.0m 002 © 2005 Fairchild Semiconductor Corporation DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPROATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com by Hang-Seok Choi, Ph. D Power Conversion Team / Fairchild Semiconductor Phone : +82-32-680-1383 Facsimile : +82-32-680-1317 E-mail : hangseok.choi@fairchildsemi.com