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FSDM311 Datasheet(PDF) 11 Page - Fairchild Semiconductor

Part # FSDM311
Description  Green Mode Fairchild Power Switch (FPS TM)
Download  19 Pages
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Manufacturer  FAIRCHILD [Fairchild Semiconductor]
Direct Link  http://www.fairchildsemi.com
Logo FAIRCHILD - Fairchild Semiconductor

FSDM311 Datasheet(HTML) 11 Page - Fairchild Semiconductor

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© 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


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