audio noise in smps


by ElectroPhysics
Tags: audio, noise, smps
ElectroPhysics
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#1
Aug18-08, 04:40 AM
P: 112
I have a problem with my switch mode power supply, smps. It creates audio sound when I power it up, especially at minimum load. As I increase the load then sound disappears and in some designs it is still there. I don't know what to do. It is a bottleneck for me. Anyone who knows what to do about it. I'm operating it at 50KHz which is well above audio frequency.
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berkeman
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#2
Aug18-08, 11:45 AM
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Quote Quote by ElectroPhysics View Post
I have a problem with my switch mode power supply, smps. It creates audio sound when I power it up, especially at minimum load. As I increase the load then sound disappears and in some designs it is still there. I don't know what to do. It is a bottleneck for me. Anyone who knows what to do about it. I'm operating it at 50KHz which is well above audio frequency.
Most likely it is magnetostriction noise in your main switching magnetic component. What topology is your SMPS? What transformer/inductor are you using? The general fix/prevention is to put some epoxy material in the gap of your transformer. Who is your transformer/inductor supplier?
ElectroPhysics
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#3
Aug19-08, 06:18 AM
P: 112
I'm using it in forward topology. etd49 as main transformer and etd39 with gape for output inductor.
I have measured the waveshape at the drain of mosfet. It looks like distorted when audio noise comes otherwise it is clean waveshape.

berkeman
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#4
Aug19-08, 11:27 AM
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audio noise in smps


Quote Quote by ElectroPhysics View Post
I'm using it in forward topology. etd49 as main transformer and etd39 with gape for output inductor.
I have measured the waveshape at the drain of mosfet. It looks like distorted when audio noise comes otherwise it is clean waveshape.
Can you find the source of the distortion/noise? Maybe a feedback stability problem?
Genius_Engg
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#5
Dec31-11, 12:13 AM
P: 1
Hey ElectroPhysics, did you solve the audible noise issue in your SMPS. Actually, I have exactly the same problem. I do not know how to get rid of this noise. Please help me out.
ElectroPhysics
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#6
Mar6-12, 04:12 AM
P: 112
@Genius
Yes partially solved. the noise is due to instability in current sensing circuitry due to leading edge spike across current sense resistor in current mode control (also in voltage mode.) there are chips which have feature of leading edge blanking circuitry built in. how ever you have to keep in mind that such chips require dummy loads as minimum load. if you can, please use cores kool u and high flux. for example from Magnetics inc.
ElectroPhysics
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#7
Mar12-12, 09:30 AM
P: 112
@Genius Engg
Yes now i think completely solved. the other part of noise was due to loose core parts. use some adhesive to fix the core parts. at the cost of damaging my designed power supply i found that even current sensing circuitry was not the only culprit. i removed the current sensing circuitry in my voltage mode control SMPS. then after giving voltage to SMPS i found that noise was still there. this proved that it was due to loose EE core parts. second time when i repeated the same experiment, something blow up due to high current in mosfets (as i have removed the current sensing/limiting circuitry), i think it was primary windings :)
ElectroPhysics
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#8
Dec10-12, 08:17 AM
P: 112
@Genius Engg and others
Now I'm in better position to tell the right reason. At light loads the current sensing circuitry measures the low current demand and lowers the duty cycle. In real scenarios this duty is so small that almost diminishing. Thus in next cycle a high primary current flows through mosfet and current sensing circuitry. This produces more than necessary power at output and thus in next cycles the cycle is skipped or duty cycle is lowered too much. One thing to be noted that this primary current when flowing at low output power is still at peak primary current level. Also this current is at random cycles. This high level of random current produces audible noise. The solution is that we can remove audible noise almost if we can keep primary current level to a lower level instead of at peak cutoff level at low output power. Then if possible we can also operate this SMPS in burst mode without danger of audio noise.
ElectroPhysics
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#9
Mar6-14, 10:19 AM
P: 112
Hi,

Here is an article on acoustic noise in SMPS based on my research uploaded at my website link,

https://sites.google.com/site/electr...acoustic-noise


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