FSDM311L Fairchild Semiconductor, FSDM311L Datasheet - Page 11

• Manufacturer Part Number: FSDM311L
• Description: IC SWIT PWM GREEN OVP HV 8SOP
• Manufacturer: Fairchild Semiconductor

Specifications of FSDM311L

• Output Isolation: Isolated
• Frequency Range: 61 ~ 73kHz
• Voltage - Input: 7 ~ 20 V
• Voltage - Output: 650V
• Power (watts): 13W
• Operating Temperature: 25°C ~ 150°C
• Package / Case: 8-SOP, 8-LSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FSDM311L_NL; FSDM311L_NL

© 2003 Fairchild Semiconductor Corporation
FSDM311 Rev. 1.1.0 • 7/14/06
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,
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
temperature cause the core and the glue to expand or
shrink at different rates.
Ceramic Capacitor
Using a film capacitor instead of a ceramic capacitor as
a snubber is another noise reduction solution. Some
dielectric
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.
Adjusting Sound Frequency
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.
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
(C
capacitor (C
(R
F
F
), opto-coupler supply resistor (R
), as shown in Figure 24.
because
bobbin,
materials
B
); and decrease a feedback gain resistor
and
sudden
show
coil;
changes
and
a
piezoelectric
the
in
D
), and feedback
chattering
the
ambient
effect,
or
11
Other Reference Materials
AN-4134: Design Guidelines for Off-line Forward
Converters Using Fairchild Power Switch (FPS™)
AN-4137: Design Guidelines for Off-line Flyback
Converters Using Fairchild Power Switch (FPS™)
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™)
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
Figure24. Typical Feedback Network of FPS
Figure 23. Equal Loudness Curves
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