1. I have ac-dc smps charger. It don't produce humming noise below 500mA. But as current increases , humming starts.I think probably it is in coil.
2. I have read some notes on internet: some says it may be damped by glueing on transformer. But i have a coil , will putting coil on it helps? I have seen some examples where glue is put on inductor itself?
Will it help? What's the prupose.
3. Second issue may be its coil may not be able to take up that current. I have ordered new coils & will see its results.
4. Any other issue?

 

1. I have ac-dc smps charger. It don't produce humming noise below 500mA. But as current increases , humming starts.I think probably it is in coil.
2. I have read some notes on internet: some says it may be damped by glueing on transformer. But i have a coil , will putting coil on it helps? I have seen some examples where glue is put on inductor itself?
Will it help? What's the prupose.
3. Second issue may be its coil may not be able to take up that current. I have ordered new coils & will see its results.
4. Any other issue?

It is physics. It happens. The more you stress the device, the more noise it will make. The metal is making the noise. You can use sound insulation and other tricks but, once the current is high enough, the sound will start. Just make sure the sheet metal or other object mechanically linked to the coil do not have a resonant frequency near the frequency of your SMPS. That is mechanical resonance, not electrical resonance.

https://en.m.wikipedia.org/wiki/Magnetostriction

 

1. I have been reading this:

http://www.thierry-lequeu.fr/data/Tiny/AN24.pdf



2. First I have replaced all the ceramic caps to check with equivalent metal film caps to check if noise goes. But noise still remains.

Now i have figured that wen I hard press the transformer from above (page 3 , figure 2 above link), noise goes away. It is vibrating.



3. I will put glue in the three legs of transformer(as shown in figure 2), to check if noise goes.