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FSD210B Datasheet(PDF) 12 Page - Fairchild Semiconductor |
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FSD210B Datasheet(HTML) 12 Page - Fairchild Semiconductor |
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12 / 18 page  FSD210B, FSD200B 12 Application Tips 1. 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 20~20,000 Hz. Even though they operate above 20 kHz, they can make noise depending on the load condition. Designers can employ several methods to reduce these noises. Here are three of these methods: 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, it also can crack the core. This is because sudden changes in the ambient temperature cause the core and the glue to expand or shrink in a different ratio according to the temperature. Ceramic Capacitor Using a film capacitor instead of a ceramic capacitor as a snubber capacitor 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 considerable to use a zener clamp circuit instead of an RCD snubber for higher efficiency as well as lower audible noise. Adjusting Sound Frequency Moving the fundamental frequency of noise out of 2~4 kHz range is the third method. Generally, humans are more sensi- tive to noise in the range of 2~4 kHz. When the fundamental frequency of noise is located in this range, one perceives the noise as louder although the noise intensity level is identical. Refer to Figure 16. Equal Loudness Curves. When FPS acts in Burst mode and the Burst operation is suspected to be a source of noise, this method may be help- ful. If the frequency of Burst mode operation lies in the range of 2~4 kHz, adjusting feedback loop can shift the Burst operation frequency. In order to reduce the Burst oper- ation 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 17. Typical Feedback Network of FPS. Figure 16. Equal Loudness Curves Figure 17. Typical Feedback Network of FPS 2. Other Reference Materials AN-4134: Design Guidelines for Off-line Forward Convert- ers Using Fairchild Power Switch (FPSTM) AN-4137: Design Guidelines for Off-line Flyback Convert- ers Using Fairchild Power Switch (FPS) AN-4138: Design Considerations for Battery Charger Using Green Mode Fairchild Power Switch (FPSTM) AN-4140: Transformer Design Consideration for Off-line Flyback Converters using Fairchild Power Switch (FPSTM) AN-4141: Troubleshooting and Design Tips for Fairchild Power Switch (FPSTM) Flyback Applications AN-4147: Design Guidelines for RCD Snubber of Flyback AN-4148: Audible Noise Reduction Techniques for FPS Applications |
Similar Part No. - FSD210B |
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Similar Description - FSD210B |
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