FSDH0265RN_05 FAIRCHILD [Fairchild Semiconductor], FSDH0265RN_05 Datasheet - Page 13

• Manufacturer Part Number: FSDH0265RN_05
• Description: Green Mode Fairchild Power Switch (FPSTM)
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

Application Tips
1. Methods of Reducing Audible Noise
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:
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.
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.
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 14. Equal Loudness Curves.
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 (C
opto-coupler supply resistor (R
(C
Figure 15. Typical Feedback Network of FPS.
Switching mode power converters have electronic and
Glue or Varnish
The most common method involves using glue or varnish
Ceramic Capacitor
Using a film capacitor instead of a ceramic capacitor as a
Adjusting Sound Frequency
Moving the fundamental frequency of noise out of 2~4 kHz
When FPS acts in Burst mode and the Burst operation is
B
) and decrease a feedback gain resistor (R
D
) and feedback capacitor
F
) as shown in
F
),
2. Other Reference Materials
AN-4134: Design Guidelines for Off-line Forward Convert-
AN-4137: Design Guidelines for Off-line Flyback Convert-
AN-4140: Transformer Design Consideration for Off-line
AN-4141: Troubleshooting and Design Tips for Fairchild
AN-4147: Design Guidelines for RCD Snubber of Flyback
AN-4148: Audible Noise Reduction Techniques for FPS
Figure 15. Typical Feedback Network of FPS
ers Using Fairchild Power Switch (FPS
ers Using Fairchild Power Switch (FPS)
Flyback Converters using Fairchild Power Switch
(FPS
Power Switch (FPS
Applications
Figure 14. Equal Loudness Curves
TM
)
TM
) Flyback Applications
FSDH0265RN, FSDM0265RN
TM
)
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