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FSDM311 Datasheet(PDF) 11 Page - Fairchild Semiconductor |
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FSDM311 Datasheet(HTML) 11 Page - Fairchild Semiconductor |
11 / 19 page © 2003 Fairchild Semiconductor Corporation www.fairchildsemi.com FSDM311 Rev. 1.1.0 • 7/14/06 11 Application Tips Methods of Reducing Audible Noise Switching mode power converters have electronic and magnetic components, which generate audible noises when the operating frequency is in the range of 20~20,000Hz. Even though they operate above 20KHz, they can make noise in some load conditions. Designers can employ several methods to reduce noise, including: Glue or Varnish The most common method involves using glue or varnish to tighten magnetic components. The motion of core, bobbin, and coil; and the chattering or magnetostriction of core, can cause the transformer to produce audible noise. The use of rigid glue and varnish helps reduce the transformer noise, but can crack the core because sudden changes in the ambient temperature cause the core and the glue to expand or shrink at different rates. Figure 23. Equal Loudness Curves Ceramic Capacitor Using a film capacitor instead of a ceramic capacitor as a snubber is another noise reduction solution. Some dielectric materials show a piezoelectric effect, depending on the electric field intensity. Hence, a snubber capacitor becomes one of the most significant sources of audible noise. It is possible to use a Zener clamp circuit instead of an RCD snubber for higher efficiency as well as lower audible noise. Figure24. Typical Feedback Network of FPS Other Reference Materials AN-4134 : Design Guidelines for Off-line Forward Converters Using Fairchild Power Switch (FPS™) Adjusting Sound Frequency AN-4137 : Design Guidelines for Off-line Flyback Converters Using Fairchild Power Switch (FPS™) Moving the fundamental frequency of noise out of the 2~4KHz range is the third method. Generally, humans are more sensitive to noise in the range of 2~4KHz. When the fundamental frequency of noise is located in this range, the noise is perceived as louder, although the noise intensity level is identical. Refer to Figure 23 for equal loudness curves. AN-4138 : Design Considerations for Battery Charger Using Green Mode Fairchild Power Switch (FPS™) AN-4140 : Transformer Design Consideration for Off-line Flyback Converters Using Fairchild Power Switch (FPS™) When FPS acts in burst mode and the burst operation is suspected to be a source of noise, this method may be helpful. If the frequency of burst mode operation lies in the range of 2~4KHz, adjusting the feedback loop can shift the burst operation frequency. To reduce the burst operation frequency, increase a feedback gain capacitor (CF), opto-coupler supply resistor (RD), and feedback capacitor (CB); and decrease a feedback gain resistor (RF), as shown in Figure 24. AN-4141 : Troubleshooting and Design Tips for Fairchild Power Switch (FPS™) Flyback Applications AN-4147 : Design Guidelines for RCD Snubber of Flyback AN-4148 : Audible Noise Reduction Techniques for Fairchild Power Switch (FPS™) Applications |
Similar Part No. - FSDM311_06 |
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Similar Description - FSDM311_06 |
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