FSQ100 查看數據表（PDF） - Fairchild Semiconductor
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FSQ100 Datasheet PDF : 12 Pages
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Application Tips
1. Methods of Reducing Audible Noise
Switching mode power converters have electronic and
magnetic components that generate audible noise when
the operating frequency is in the range of 20~20,000Hz.
Even though they operate above 20kHz, they can make
noise, depending on the load condition. Designers can
employ several methods to reduce noise.
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. This is because sudden changes in the ambient
temperature cause the core and the glue to expand or
shrink in a different ratio.
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 possible to use a Zener
clamp circuit instead of an RCD snubber for higher
efficiency as and lower audible noise.
Adjusting Sound Frequency
Moving the fundamental frequency of noise out of
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 22
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
helpful. If the frequency of burst-mode operation lies in
the range of 2~4 kHz, 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 23.
Figure 22. Equal Loudness Curves
Figure 23. Typical Feedback Network of FPS™
2. Reference Materials
AN-4134: Design Guidelines for Off-line Forward
Converters Using Fairchild Power Switch (FPSTM)
AN-4137: Design Guidelines for Off-line Flyback
Converters Using Fairchild Power Switch (FPSTM)
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
FPSTM Applications
© 2007 Fairchild Semiconductor Corporation
FSQ100 Rev. 1.0.1
10
www.fairchildsemi.com
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