LNK625 and Myrra 74000 audible noise

Sorry to hear the audible noiose problem. I beleive AN24 can help you somehting. PLS find it via the following LNK:  http://www.powerint.com/sites/default/files/product-docs/an24.pdf

Regards

Dear,

I thank you for your quick answer, we've seen the AN24 and are trying to applied it the best as we can.

When we designed the supply we done it very close to the figure 2 of RDR-201 (same value of component for the snubber).

Do you know if the myrra transformer is used to be noisy?

We will try to replace our capacitor with the same one you used in the figure 2. Do you know if this supply is generating noise?

Thanks 

Fabrizio

I guess the cap you mentioned is used for the RCD snubber in the primary side. AN24 claims that the snubber cap is very important for audible noise design. So PLS replace it with a film cap, and to see if the noise can be solve.

For the transformer, I have asked several enginner at PI, and unfortuantely we do not have any idea about that. But definitely, transformer is very important for the noise too.

again, AN24 has three possible solutions on the first page, and they are pasted as beow.

Regards

Quick Guide for TinySwitchTM Designs
The ON/OFF control used in TinySwitch can generate audio
noise in the clamp capacitor and the transformer at certain
load conditions. The following simple design steps can be
taken to dramatically reduce audible noise at virtually no
added cost.
1. Some types of ceramic capacitors used in primary clamp
circuitry can be very noisy. Replace the ceramic capacitor
with a plastic film capacitor or use a Zener clamp. Zener
clamps are now comparable in cost to RCD clamps, take up
much less space and also provide higher efficiency. Ceramic
capacitors used in RC snubbers connected to the DRAIN
rarely generate audio noise (See Figure 1).
2. Construct the transformer using one of the techniques
described in this application note. Gluing with glass spacer
beads on all three legs is recommended because it has
superior structural integrity with temperature changes,
independent of the spacing between cores. This technique
also eliminates the need to gap the core, saving cost. In
contrast, conventional gluing (with hard glue) of center
gapped cores needs to be checked over the specified
temperature range for structural integrity, especially for
gaps in excess of 0.1 mm. Potting is another option at a
slightly higher cost.
3. If further audio noise reduction in the transformer is
desired, use a lower peak flux density. Changing the peak
flux density from 3000 gauss

Dear PI.

I thank you for this information we've closely look at all suspected component. We are lucky to have Laser VibrometerDoppler instrument. So we were able to clearly see which component is moving. 

In our case it is the Myrra transformer. We clearly see the magnetic moving.

We try to isolate it with some hot-glue but nothing changed. 

Do you have some advice for an equivalent transformer? or some product with which we can try to reduce this noise?

I thank you in advance

Regards

Laconte -

One of the issues with using off the shelf magnetics is that you have no control over the design and construction of the parts.  If you're determined to keep using the Myrra 74000, you could try vacuum impregnating the transformers and see if that helps with the acoustics.  

Otherwise, my advice would be to design a transformer for your specific application.  If you can find an off the shelf unit that matches the specs of the transformer you designed, great.  If not, have someone build it for you.

-The Traveler

Dear Traveler.

I thank you for your answer. We will try some varnishing around the transformer and then made our own design. 

My issue is that as we haven't identify clearly what is the problem with this transformer to have the same issue with our own design.

Regards

Fabrizio

Are you saying that initial transformer prototypes built in-house (by you) don't exhibit this problem but that the Myrra 74000 transformers do exhibit the problem?

-The Traveler