DM0265RL データシートの表示（PDF） - Fairchild Semiconductor

部品番号

コンポーネント説明

メーカー

DM0265RL

DMO265R = DM0265R FAIRCHILD / FSDH0265RN, FSDM0265RN

Fairchild Semiconductor 

Application Tips

FSDH0265RN, FSDM0265RN

1. 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 20~20,000 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:

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, 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.

Figure 14. Equal Loudness Curves

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 considerable to use a zener clamp circuit instead

of an RCD snubber for higher efficiency as well as lower

audible noise.

Figure 15. Typical Feedback Network of FPS

Adjusting Sound Frequency

Moving the fundamental frequency of noise out of 2~4 kHz

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.

When FPS acts in Burst mode and the Burst operation is

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 (CF),

opto-coupler supply resistor (RD) and feedback capacitor

(CB) and decrease a feedback gain resistor (RF) as shown in

Figure 15. Typical Feedback Network of FPS.

2. Other Reference Materials

AN-4134: Design Guidelines for Off-line Forward Convert-

ers Using Fairchild Power Switch (FPSTM)

AN-4137: Design Guidelines for Off-line Flyback Convert-

ers Using Fairchild Power Switch (FPS)

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 FPS

Applications

13

Share Link: