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"Noisy" switch power supply can solve this, you know?

Who work done development personnel have such experience, test switch power supply or have heard similar products in the experiment playing bad leakage noise or high pressure the arc sound uninvited: its sound or big or small, or sometimes not; Its rhythm or deep or harsh, or fickle. 
Audio noise generally refers to the switch power supply itself in the process of work, can be ear heard for 20-20 KHZ audio frequency signal. Electronic and magnetic components of oscillation frequency within the scope of the human ear hearing, can hear the signal is produced. This kind of phenomenon in power transformation has already known at the beginning of the study. With 50 and 60 hz power frequency transformer often work hates noise. If the load modulation with audio component, working at a constant ultrasonic frequency switch power converter also produces audio noise. 
Low power electricity at ordinary times, audio signal usually has nothing to do with the converter. However, the designer may want to lower its acoustic emission circuit. Low power AC to DC converters, the 50 or 60 hz transformer core chips welded together, can make the level of noise to allow communication. Ferrite transformer in high frequency switch converter also similar technology in wood. 
Advanced audio engineering equipment used to study the sound radiation of switch power supply. This device can be very accurately measuring absolute sound pressure level and sound spectrum, but the human sense of sound is very subjective. It's hard to say how much of a voice is heard, what is more difficult to determine how much sound in specific applications will be considered intolerable noise. 
Acoustic radiation and electromagnetic radiation are similar, but there is no general benchmark used to measure the tolerance of auditory. Therefore, the designer can according to the following guidelines to deal with the problem related to audio noise, reduce the sound radiation of the product. 
The power and the suppression method of audio noise 
A: the audio noise transformer 
In most of the flyback converter applications, audio transformer is the main noise source. Test plate on the prototype of the first transformer noise are often surprising. Adopts the structure known as the appropriate skills to basically eliminate noise without additional costs. Pay attention to the finished product performance on assembling prototype transformer of repeatability. 
There is some mechanism will produce transformer noise, each will produce sound mechanical displacement. These mechanisms include: 
Relative motion - core attraction between the two parts to make it move, oppression will its separation medium. 
Impact - if two pieces of the surface of the magnetic core can contact, they will move in response to the magnetic flux incentive make the collision or scratch. 
Bending - only in EE or EI structure is the core of the middle leg fracture, can make the magnetic core parts along with the direction of the appeal. 
Magnetostrictive - the size of the magnetic core material changing with the magnetic flux density. Ordinary power ferrite the rate of change of less than 1 PPM. 
Skeleton move - the core group of displacement can be transmitted by skeleton and amplification. 
Moving coil - current in a coil to produce the attraction and repulsion of the wire. 
Mobile source work together, to form the complex mechanical system, it can within the scope of the human ear hearing one or several frequency point, a strong resonance. Under 10 w off-line flyback converter type commonly used structure generally produce resonance of 10 KHZ to 20 KHZ. When the magnetic flux of motivation fundamental frequency or its harmonics through the mechanical resonance area, mobile sound. Designers should transform to load all the test audio noise, especially in need of dynamic load. 
These mechanisms, the size of the noise according to their different location decision. Fortunately, the designer can use simple structure technology to effectively audio noise attenuation mechanism. 
The following simple explanations can effectively audio noise attenuation mechanism of common method. 
First transformer to homogeneous immersion, thus effectively between the coil and the coil, the coil and the skeleton, skeleton, and between the inherent gap between core, reduce the possibility of displacement of the moving parts, if necessary can be magnetic components and circuit board interface is filled with white glue or spraying anti-corrosion paint, further reduce the mechanical vibration of space, effectively reduce the noise. 
In situations where conditions permit to reduce the peak magnetic flux density, high temperature should be fully considered when the saturation magnetic flux density, leave enough margin to prevent work curve into the nonlinear area, the audio noise, can effectively reduce the transformer has proved peak magnetic flux density gaussian drop from 3000 to 2000 5 db gaussian noise can be reduced to 15 db. 

Conditions allow you can use the amorphous, superfine crystal alloy soft magnetic materials, such as their uniform consistency is far better than general ferrite magnetic, magnetostrictive effect tends to zero, therefore, is not sensitive to stress. 


----------Archled Technology Co.,Limited


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E-mail: mack@archled.net

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