FSDM311A Fairchild Semiconductor, FSDM311A Datasheet - Page 10

• Manufacturer Part Number: FSDM311A
• Description: IC SWIT PWM GREEN OVP HV 8DIP
• Manufacturer: Fairchild Semiconductor

Specifications of FSDM311A

• 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-DIP (0.300", 7.62mm)
• On Resistance (max): 14 Ohms
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 25 C
• Maximum Power Dissipation: 1400 mW
• Mounting Style: Through Hole
• Supply Current: 1.5 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2007 Fairchild Semiconductor Corporation
FSDM311A • Rev.1.0.2
Application Information
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,
magnetostriction of core, can cause the transformer to
produce audible noise. The use of rigid glue and
varnish helps reduce 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 at a different rate.
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. 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 out of the 2~4kHz
range another method of reducing perceptible noise.
Generally, humans are more sensitive to noise in the
range of 2~4kHz. When the fundamental frequency of
noise is located in this range, it is perceived as louder,
although the noise intensity level is identical (refer to
Figure 23, Equal Loudness Curves).
If burst-mode operation is suspected to be a source of
noise, this method may be helpful. If the frequency of
burst-mode operation lies between 2~4 kHz, adjusting
the feedback loop can shift the frequency. To reduce
the burst operation frequency, increase a feedback gain
capacitor (C
feedback capacitor (C
resistor (R
bobbin,
F
), as shown in Figure 24.
F
), opto-coupler supply resistor (R
and
B
); and decrease a feedback gain
coil;
and
the
chattering
D
), and
or
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
FPS™ Applications
10
Figure 24. Typical Feedback Network of FPS™
Figure 23.
Equal Loudness Curves
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