Linkswitch-3 LNK6404D - generic design questions

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Hello,

I have a transformer design for LNK6404D.
Looking into expanding it's usage for different products but there are some thing I would like to address.

1. Current design has barely audible acoustic noise.
I'm planning to use it in semi-open enclosures so it is first thing to fix. Changing BM_TARGET from 1800 to 1500 seems to help in reducing sound to almost non-existant.
Are there any other parameters that could be looked into to reduce acoustic noise?

2. Tight fit due to TIW secondary winding
For transformer test samples with reduced BM_TARGET suggested secondary windings with TIW cannot be fit to EF12.6 transformer.
What are negatives of reducing TIW wire gauge other than increased loss due to higher resistance and lower efficiency?

Current transformer design in use : piexpertonline.power.com/piexpert/design/select?share=e84517ab445d704697ca17209de230fbe4745f04d715a43a9531d34a5fae64ce

Hi DariusP

Thanks for taking time to use Power Integration Product.
1. Audible Noise Reduction
-Reduce BM
-Bias winding capacitor use electrolytic capacitor
-Varnish Transformer
-Varnish differential mode choke
-Use NPO/COG SMD ceramic capacitor
-Transformer glue between the bobbin and the core and also on the legs where core faces meet.

2. Aside from increases loss due to high resistance and lower efficiency, you should also look into the thermals of the Transformer.

Thanks

Regards

PI-Chloe

Hi DariusP

Thanks for taking time to use Power Integration Product.
1. Audible Noise Reduction
-Reduce BM
-Bias winding capacitor use electrolytic capacitor
-Varnish Transformer
-Varnish differential mode choke
-Use NPO/COG SMD ceramic capacitor
-Transformer glue between the bobbin and the core and also on the legs where core faces meet.

2. Aside from increases loss due to high resistance and lower efficiency, you should also look into the thermals of the Transformer.

Thanks

Regards

PI-Chloe

Thanks for information.

Tried all suggestions and managed to get noise down but still a bit too high.

So currently remaining attempt is to reduce BM further. Current sample is designed with around BM 1500 and it generates acoustic noise, transformer is most likely source at the moment.

So to further reduce acoustic noise we should try lower BM further?
Should both peak Bm and working Bm be around 1500?

Hi Darius,

1500 Bm Ok.

You can add adhesive TRF to PCB to lessen the audible noise.
Did you apply varnish to the TRF?

Thanks

Regards

Patrick

Tried both varnished and unvarnished transformers.
Applying additional adhesives and covering transformer reduces noise significantly. Looking into possible options for assembly and/or manufacturing to see what we can apply.
Thanks for support.